International Journal of Systematic Bacteriology (1999), 49, 415­440 Printed in Great Britain
Emended description of the order Chlamydiales,
proposal of Parachlamydiaceae fam. nov. and
Simkaniaceae fam. nov., each containing one
monotypic genus, revised taxonomy of the
family Chlamydiaceae, including a new genus
and five new species, and standards for the
identification of organisms
Karin D. E. Everett,1
 Robin M. Bush2
and Arthur A. Andersen1
Author for correspondence: Karin D. E. Everett. Tel: j1 706 542 5823. Fax: j1 706 542 5771.
e-mail: keverett!calc.vet.uga.edu or kdeeverett!hotmail.com
1 Avian and Swine
Respiratory Diseases
Research Unit, National
Animal Disease Center,
Agricultural Research
Service, US Department of
Agriculture, PO Box 70,
Ames, IA 50010, USA
2 Department of Ecology
& Evolutionary Biology,
University of California
at Irvine, Irvine,
CA 92696, USA
The current taxonomic classification of Chlamydia is based on limited
phenotypic, morphologic and genetic criteria. This classification does not take
into account recent analysis of the ribosomal operon or recently identified
obligately intracellular organisms that have a chlamydia-like developmental
cycle of replication. Neither does it provide a systematic rationale for
identifying new strains. In this study, phylogenetic analyses of the 16S and 23S
rRNA genes are presented with corroborating genetic and phenotypic
information to show that the order Chlamydiales contains at least four distinct
groups at the family level and that within the Chlamydiaceae are two distinct
lineages which branch into nine separate clusters. In this report a reclassification
of the order Chlamydiales and its current taxa is proposed. This proposal
retains currently known strains with 90% 16S rRNA identity in the family
Chlamydiaceae and separates other chlamydia-like organisms that have
80­90% 16S rRNA relatedness to the Chlamydiaceae into new families.
Chlamydiae that were previously described as `Candidatus Parachlamydia
acanthamoebae' Amann, Springer, Scho$ nhuber, Ludwig, Schmid, Mu$ ller and
Michel 1997, become members of Parachlamydiaceae fam. nov., Parachlamydia
acanthamoebae gen. nov., sp. nov. `Simkania ' strain Z becomes the founding
member of Simkaniaceae fam. nov., Simkania negevensis gen. nov., sp. nov.
The fourth group, which includes strain WSU 86-1044, was left unnamed. The
Chlamydiaceae, which currently has only the genus Chlamydia, is divided into
two genera, Chlamydia and Chlamydophila gen. nov. Two new species,
Chlamydia muridarum sp. nov. and Chlamydia suis sp. nov., join Chlamydia
trachomatis in the emended genus Chlamydia. Chlamydophila gen. nov.
assimilates the current species, Chlamydia pecorum, Chlamydia pneumoniae
and Chlamydia psittaci, to form Chlamydophila pecorum comb. nov.,
Chlamydophila pneumoniae comb. nov. and Chlamydophila psittaci comb. nov.
Three new Chlamydophila species are derived from Chlamydia psittaci:
Chlamydophila abortus gen. nov., sp. nov., Chlamydophila caviae gen. nov., sp.
nov. and Chlamydophila felis gen. nov., sp. nov. Emended descriptions for the
.................................................................................................................................................................................................................................................................................................................
 Present address: Departmentof Medical Microbiology and Parasitology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7371, USA.
Abbreviations: CCon, Chlamydia consensus 16S rRNA sequence; EB, elementary body; LGV, lymphogranuloma venereum; MLE, maximum-likelihood
estimate; MN, meningopneumonitis; MOMP, major outer-membrane protein; NJ, neighbour-joining; RB, reticulate body.
The GenBank accession numbers for the sequences used in this paper are given in Figs 1 and 2 and Tables 2 and 3.
00787 # 1999 IUMS 415
K. D. E. Everett, R. M. Bush and A. A. Andersen
order Chlamydiales and for the family Chlamydiaceae are provided. These
families, genera and species are readily distinguished by analysis of signature
sequences in the 16S and 23S ribosomal genes.
Keywords: Chlamydiales, taxonomy, ribosomal, human pathogens, animal pathogens
INTRODUCTION
Members of the order Chlamydiales are obligately
intracellular bacteria. They exhibit a two-stage developmental
cycle of replication: the infectious bacterial
form is endocytosed by eukaryotic cells and
resides within a cytoplasmic inclusion, where it transforms
into a vegetative form and replicates by binary
fission (Moulder, 1991). As an inclusion fills with
progeny, chlamydiae transform back into the metabolically
inactive, infectious form and are released
through host cell rupture or fusion of the inclusion\
plasma membranes. Chlamydiae are disseminated by
aerosol or by contact, requiring no alternate vector. Of
the fifteen or more major groupings in the domain
Bacteria (Stackebrandt et al., 1997; Van de Peer et al.,
1994), Chlamydiales is the only lineage whose known
members are exclusively intracellular parasites of
members of the domain Eucarya.
The order Chlamydiales currently has one family, the
Chlamydiaceae, containing one genus and four species
(Herring, 1993). When the Approved Lists of Bacterial
Names was published in 1980, the Chlamydiaceae had
just two species (Skerman et al., 1980). At that time, all
bacteria with chlamydia-like chemical characteristics,
morphology and developmental replication belonged
to either Chlamydia trachomatis or Chlamydia psittaci
in the order Chlamydiales (Page, 1966, 1968; Storz &
Page, 1971). Chlamydia trachomatis strains were identified
by their accumulation of glycogen in inclusions
and their sensitivity to sulfadiazine. Chlamydia psittaci
strains did not accumulate glycogen and were usually
resistant to sulfadiazine. The establishment of this
classification was a milestone in chlamydial taxonomy,
as it renounced reliance on presumed host, on presumed
tissue preference and on serology in grouping
these organisms.
Before 1980, however, isolations had already been
made that would not fit into these two species
(Darougar et al., 1980; Dwyer et al., 1972; Forsey &
Darougar, 1984). The development of DNA-based
classification methods during the 1980s provided new
techniques for differentiating chlamydial groups.
DNA­DNA reassociation, in particular, was established
as a tool for distinguishing species ( 70%
homology) and genera ( 20% homology) (Amann et
al., 1995; Schleifer & Stackebrandt, 1983; Wayne et
al., 1987). According to these criteria, DNA­DNA
reassociation studies of new chlamydial strains and of
strains placed in the ATCC collection prior to 1971
supported eight groups on the level of genus or species
(Table 1). These data contributed to the creation of
two additional species, Chlamydia pneumoniae
(Grayston et al., 1989) and Chlamydia pecorum
(Fukushi & Hirai, 1992). In 1993, DNA sequence
analysis identified an isolate from a ninth chlamydial
group, Chlamydia trachomatis-like Chlamydia from
swine (Kaltenboeck et al., 1993). Since then, a number
of closely related swine isolates and variants have been
reported (Everett & Andersen, 1997; Kaltenbo$ ck et
al., 1997; Kaltenboeck & Storz, 1992; Rogers et al.,
1993, 1996; Rogers & Andersen, 1996; Schiller et al.,
1997). These strains cannot be designated as
Chlamydia trachomatis using current criteria, as many
of these strains are resistant to sulfadiazine (Andersen
& Rogers, 1998). The nine clusters in the Chlamydiaceae
are supported by analyses of phenotype,
antigenicity, associated disease, host range, biological
data and genomic endonuclease restriction (Everett &
Andersen, 1997). Genetic data, including recent phylogenetic
analyses using the ribosomal operon, are also
consistent with the presence of nine groups in the
Chlamydiaceae (Everett & Andersen, 1997;
Kaltenboeck et al., 1993; Pudjiatmoko et al., 1997;
Takahashi et al., 1997).
Species within the Chlamydiaceae have 16S rRNA
gene sequences that are 90% identical (Pettersson et
al., 1997; Pudjiatmoko et al., 1997; Takahashi et al.,
1997). All strains in the Chlamydiaceae are recognized
by monoclonal antibodies (mAbs) that detect the
LPS trisaccharide Kdo-(2 8)-Kdo-(2 4)-Kdo
(Lo$ bau et al., 1995). Four additional groups of
chlamydia-like organisms have been recently identified
that have 80% 16S rRNA gene sequence identity
with chlamydiae: (i) the `Simkania' strain Z (Kahane
et al., 1995, 1999); (ii) strains of `Hall's coccus' (Birtles
et al., 1997) and the closely related `Candidatus
Parachlamydia acanthamoebae' Amann et al. 1997
(Amann et al., 1997), all of which were isolated from
amoebae; (iii) an agent identified as a cause of bovine
abortion that was initially described as a rickettsia
(Dilbeck et al., 1990; Kocan et al., 1990; Rurangirwa
et al., 1999); and (iv) a cluster of isolates from amoebae
(T. Fritsche, personal communication; Gautom et al.,
1996). These bacteria meet the requirement for inclusion
in Chlamydiales because they are obligate
intracellular bacteria that have the chlamydia-like
developmental cycle of replication. Inclusion of these
novel chlamydia-like agents in Chlamydiales meets
criteria recently established to define a bacterial class
based exclusively on 80% 16S rRNA gene sequence
identity (Stackebrandt et al., 1997). However, because
the new groups at present include just a few species, a
decision regarding whether Chlamydiales should become
a class or remain an order can be deferred until
more information on these and other new chlamydial
416 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
Table 1. Chlamydia spp. percentage similarity using DNA­DNA reassociation (Chlamydia suis not tested)
.................................................................................................................................................................................................................................................................................................................
The total number of strains (n) that were used in these studies is shown for each species in the row heading, but many of the
comparisons were performed with only a subset of these strains.
8 7 6 5 4 3 2 1
1 Chlamydia trachomatis (n l 8) 5* 6­11*, 18­24 5­6*, 5­15 7­12, 11§, 5*,
15­33
4­32 5­7* 65§, 20­52 100§, 97­100*,
92­100
2 Chlamydia muridarum (n l 1) ­ 1­10 2­6 11§, 3­20 1­4 ­ 100
3 Chlamydophila pneumoniae (n l 4) 5­8* 6­8* 6­10* 5­7* 10 94­100*, 94­96
4 Chlamydophila pecorum (n l 3) ­ 9­12 1 1­19 88­100
5 Chlamydophila psittaci (n l 6) 20­35* 21­37*, 31­33 63­85*, 27­85 100§, 93­100*,
73­100
6 Chlamydophila abortus (n l 2) 27­38* 24­37*, 14­33 100*
7 Chlamydophila felis (n l 2) 30­33* 100*
8 Chlamydophila caviae (n l 1) 100*
* Cox et al. (1988).
 Fukushi & Hirai (1989). Note also that interspecies analyses were carried out with one Chlamydophila pecorum strain, and that
Chlamydophila pecorum intraspecies analysis used three.
 Kingsbury & Weiss (1968).
§ Weiss et al. (1970).
 Fukushi & Hirai (1992).
groups has become available. It seems likely that
culture-free PCR techniques and DNA sequencing will
soon expand our understanding of diversity within
Chlamydiales and this will help resolve questions about
higher level classification.
A reclassification of chlamydiae based on 16S rRNA
sequence similarity clusters, on analyses of full-length
16S and 23S rDNAs, and on phenotypic and ecologic
differentiation (Palys et al., 1997) solves a number of
current problems in chlamydial taxonomy. It provides
a consistent method for identifying present taxa and a
logical basis for defining new taxa using criteria that
are comparable to those being established for other
major bacterial lineages. It provides appropriate
groupings for pathogens with distinctive underlying
genetic relationships and diverse, well-established
patterns of virulence. It further provides a usable
system for organizing chlamydial data in the international
sequence databases.
The purpose of this report is to update the description
of taxa in the order Chlamydiales, presenting criteria
that distinguish Parachlamydiaceae fam. nov.,
Simkaniaceae fam. nov. and Chlamydiaceae and designating
appropriate genera and species within the
Chlamydiaceae. To accomplish this, phylogenetic trees
were constructed using 16S and 23S rRNA sequences
from a number of strains within the Chlamydiaceae
and closely related strains. To aid in the identification
of new strains, `signature sequence' segments for PCR
amplification and sequencing were identified in the 16S
and 23S rRNA genes. Information was compiled for
the descriptions of species, chlamydial genome sizes
and the presence or the absence of extrachromosomal
plasmids. We offer the following proposal for revision
of groupings within the order Chlamydiales, with two
new families within the Chlamydiales and establishing
a new genus and five new species in the Chlamydiaceae.
In this paper, the new names or combinations have
only been used in the text following their first mention
in the descriptions. However, the new names and
combinations have been used throughout the tables
and figures.
METHODS
Bacterial strains. Chlamydia strains that were used for 23S
rRNA gene analysis included Chlamydia pneumoniae TW-
183T, Chlamydia pecorum IPA, Chlamydia psittaci NJ1,
6BCT, GPIC, FP Baker, Chlamydia trachomatis A\Har-13T,
L2\434\BU, MoPn, SFPD and the Chlamydia trachomatislike
swine strain R22 and were obtained from previously
described sources (Everett & Andersen, 1997). `Simkania' Z
was obtained from preparations of HeLa and Vero cells, and
was identical to `Simkania' Z1, which was a subculture of
`Simkania' Z (Everett & Andersen, 1997; Kahane et al.,
1993). Strain WSU 86-1044 was obtained from Fred
Rurangirwa at the Washington Animal Disease Diagnostic
Laboratory (WADDL) in Pullman, WA, USA. Chlamydial
strains used for PFGE, extrachromosomal plasmid analysis,
and testing of primers for signature sequence analysis were
obtained from previously described sources (Everett &
Andersen, 1997). Escherichia coli strain JM109 used in
PFGE was obtained from Francis E. Nano (currently at
University of Victoria, Victoria, BC, Canada).
Sequence and phylogenetic analysis. Oligonucleotide primer
synthesis and DNA sequencing were performed by the Iowa
State University DNA Sequencing and Synthesis Facility,
Ames, IA, USA. Both the coding and the complementary
strands were sequenced. The Sequencher data analysis
software (Gene Codes) was used to assemble the 23S rRNA
gene sequences. Sequence analysis programs described in the
Program Manual for the Wisconsin Package (Genetics
Computer Group, 1994) were used for DNA and RNA
analyses. These programs were Reformat, SeqEd, Assemble,
PILEUP, LineUp, Distances, FoldRNA and SQUIGGLES.
For phylogenetic analyses of the complete 16S rRNA genes,
sequence data were retrieved from GenBank and extended
to full-length as necessary using data from a recent study
International Journal of Systematic Bacteriology 49 417
K. D. E. Everett, R. M. Bush and A. A. Andersen
(Everett & Andersen, 1997). The 16S rDNA from strain
SFPD was resequenced; the 16S rRNA and 16S­23S
intergenic spacer sequence for strain WSU 86-1044 were
provided by Fred Rurangirwa (Department of Veterinary
Microbiology and Pathology, Washington State University,
Pullman, WA, USA). The 23S rRNA sequences from strain
WSU 86-1044 and `Simkania' strain Z were obtained
directly from PCR products. Full-length 23S rRNA sequence
data for phylogenetic analysis were obtained from
PCR-amplified segments that supplemented data previously
obtained (Everett & Andersen, 1997). Two PCR primers
were used for these amplifications: primer 6F matching the
coding strand of the Chlamydia 23S rRNA (5h GGATGAGTTGTGAATAGG
3h) and a complementary primer
that PCR amplifies the 5S gene of Brucella abortus (5h
AGTTCGGGATGGGATCGGGTG 3h). Additional
primers were used to sequence both the PCR products and
the cloned PCR-product templates. PCR conditions for all
amplifications using AmpliTaq DNA polymerase (Perkin
Elmer) were 30 s at 94 mC, 15 s annealing, 30 s at 72 mC in the
GeneAmp PCR System 9600 thermal cycler (Perkin Elmer).
Annealing temperatures were specific for each primer set.
The 3h end of each " 3000 bp 23S rRNA gene was
determined by FoldRNA analysis of sequence data for the
intergenic spacer that had been spliced, by computer, to
sequence data for a 200 base segment of 23S rRNA extending
into the 5S gene. The 5h end of the 23S rRNA genes in 6BCT,
NJ1 and R22 had previously been identified by primer
extension analysis (Everett & Andersen, 1997).
For phylogenetic analysis, full-length 16S rRNA and 23S
rRNA data were aligned using CLUSTAL W (Thompson et al.,
1994). There were several short segments in the 23S rRNA
which were difficult to align, however, the results are robust
with respect to alternative alignment decisions and also to
the removal of these segments. The 3h ends of both genes
were trimmed to produce sequences of even length: 1558 nt
positions were analysed for the 16S rRNA gene and 2956 nt
positions were analysed for the 23S rRNA gene. Phylogenetic
trees were generated using the maximum-parsimony
and neighbour-joining routines of PAUP 4.0.0d63 (Swofford,
1993). PAUP's heuristic search parameters were set to
trunk­bisection­resection branch swapping with no limit on
the number of trees held per run, and with branches having
a maximum length of zero collapsed to yield polytomies.
Branching order reliability was evaluated by 1000 replications
of bootstrap resampling using parsimony
(Felsenstein, 1985). Trees were also constructed using the
maximum-likelihood routine DNAML of PHYLIP 3.5c
(Felsenstein, 1993). Parsimony and maximum-likelihood
trees were both generated using 10 replicate runs in which
the input sequences were read in random order. Saturation
plots were constructed contrasting phyletic versus pairwise
distances for each tree. Non-linearity of these plots would
suggest that excessive homoplasy could be responsible for
nodes being joined at random rather than due to similarity
(Vuillaumier et al., 1997).
Signature sequence identification. `Signature sequence'
segments were identified by examining chlamydial 16S
rRNA gene sequences and partial chlamydial 23S rRNA
gene segments, most of which are currently in the GenBank
database. Signature segments were narrowly defined regions
of sequence that were conserved and distinctive for each of
nine groups. The 16S signature segments were determined
from the 59 discrete chlamydial 16S rRNA genes in
GenBank plus the Chlamydia pneumoniae Koala sequence
from strain Con. There were 5 representative strains
from six of the nine groups in the Chlamydiaceae and fewer
strains in the other groups. The partial 23S rRNA sequences
used to identify the 23S signature sequence included 50
strains, with 5 representative strains from each of five of
the nine groups in the Chlamydiaceae and fewer strains in the
other groups. The 298 base 16S signature sequence could be
PCR-amplified and sequenced using 51 mC annealing and
primers which matched all chlamydiae: 16SIGF (5h CGGCGTGGATGAGGCAT
3h), which matched the 16S rRNA
gene at position 40, and 16SIGR (5h TCAGTCCCAGTGTTGGC
3h), which complemented the 16S rRNA gene at
position 337 (E. coli and Chlamydia numbering). The rDNA
template was PCR amplified with AmpliTaq DNA polymerase
as described above. In some cases, the rRNA
template was reverse transcribed and PCR was performed in
a single reaction mix using the GeneAmp EZ rTth RNA
PCR Kit (Perkin Elmer). PCR products were filtered with
Microcon 100 microconcentrators (Amicon) prior to
sequencing.
The 23S signature sequence, which was domain I of the 23S
rRNA gene, was PCR-amplified and partially sequenced
using either or both of two strategies. The first strategy was
applied to reverse-transcribed rRNA or to rDNA template
to amplify a 600 bp PCR product containing most of the
signature sequence. This strategy used two conserved bacterial
primers, U23F (5h GATGCCTTGGCATTGATAGGCGATGAAGGA
3h) and 23SIGR (5h TGGCTCATCATGCAAAAGGCA
3h) (annealing temperature 61 mC),
which can also amplify non-chlamydial rRNAs. These
primers were used in direct sequence analysis of PCR
products that were filtered with Microcon 100 microconcentrators.
For the Chlamydiaceae strains, a second
strategy was also used to characterize the 23S signature
sequence. A 1 kbp product was PCR-amplified from rDNA
template using primers 16SF2 (5h CCGCCCGTCACATCATGG
3h) and 23SIGR (5h TGGCTCATCATGCAAAAGGCA
3h). This amplicon contained a complete 627 bp
domain I segment, the 220 bp intergenic spacer, and
150 bp of the 16S rRNA gene; domain I was fully sequenced
using primers 16SF2, 23SIGR, IGSIGF (5h ATAATAATAGACGTTTAAGA
3h) and 23R (5h TACTAAGATGTTTCAGTTC
3h).
PFGE. DNA plugs of 1% (w\v) low-melting-point agarose
that contained Renografin-purified chlamydiae were prepared
for PFGE. Pellets of chlamydiae and chlamydiaeinfected
cells were resuspended in 40% (w\v) Renografin
(Solvay Animal Health) in PBS containing Ca#+ and Mg#+
(Sambrook et al., 1989), incubated for 10 min at room
temperature, and diluted in at least 2 vols PBS. Lysed hostcell
DNA was sheared by repeated pipetting. Chlamydiae
were then pelleted at 10000 r.p.m., resuspended in a few
microlitres of PBS, mixed with 1% LMP agarose at 37 mC,
and cooled in aliquots in a plug mould (Bio-Rad
Laboratories). After refrigeration, the plugs were sequentially
incubated in several buffers: 50 mM DTT, 30 mM
Tris, 10 mM EDTA pH 9n0 at 37 mC overnight; 10 mM Tris,
10 mM EDTA pH 8n0 (TE) with DNase-free RNase
(Boehringer Mannheim) at 37 mC for 5 h; TE containing
10 g Proteinase K ml-" (Gibco BRL Life Technologies) at
50 mC overnight; and TE at 4 mC, with four or more changes
of TE over a period of a week or more.
Intitially, the plugs were subjected to 4 krad (40 gray) of
gamma irradiation (Walker et al., 1991) to linearize chromosome
prior to electrophoresis. Chromosome from treated
and untreated plugs, however, showed no reproducible
differences in electrophoretic mobility. Subsequently, there-
418 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
fore, radiation treatment was removed from the protocol.
The plugs were inserted into a 1% (w\v) agarose gel
(12n5i12n5i1n2 cm) and electrophoresed at 150 V, 14 mC
using the CHEF-DR Drive Module, Pulsewave 760, and
power supply model 200\2.0 (Bio-Rad) with recirculating
buffer containing 22n5 mM Tris\borate, 1 mM EDTA. A
pulse time of 2 min was applied for 24 h, the buffer was
replaced with fresh buffer, then a pulse time of 4 min was
applied for 30 h (Bergthorsson & Ochman, 1995). Gels were
stained with Sybr Green I nucleic acid stain (FMC
BioProducts) (not shown) or with ethidium bromide. PFGE
II size markers (Boehringer Mannheim) were used.
Southern blot analysis. An oligonucleotide primer
recognizing the origin of replication of all known chlamydial
plasmids was synthesized. This 102 base primer consisted of
four direct repeats with a restriction site at each end
(Integrated DNA Technologies): GCGGCCGC[TTGCAA-
CT(T\C)T(T\A)GGTGGTAGACT]
%
CCCGGG. The
primer was 5h end-labelled with [-$#P]ATP [ICN; 10 Ci
l-" (3n7i10& Bq l-"), 4500 Ci mol-$ (1n665 i 10"% Bq
mol-%)] using T4 polynucleotide kinase (GibcoBRL Life
Technologies). The 25 l labelling reaction was stopped by
the addition of 75 l H
#
0 and 50 l 7n5 M ammonium acetate.
Labelled primer was precipitated by adding 5 l 5 mg tRNA
ml-" in H
#
0, then adding 450 l 95% ethanol, followed by
centrifugation. Chlamydial DNA that was embedded in
agarose plugs (above) was separated by standard electrophoresis
in 1i TBE on 1% (w\v) agarose gels (10i6n5 cm,
or 10i14 cm). A DNA size standard, 1 kb DNA Ladder
(GibcoBRL Life Technologies), was electrophoresed at the
same time. After electrophoresis, the separated DNAs were
denatured by soaking the gel for 45 min in several vols of
1n5 M NaCl, 0n5 M NaOH at 4 mC; neutralized in 1 M Tris
pH 7n2, 1n5 M NaCl (Sambrook et al., 1989); transferred to
a Hybond-Nj nucleic acid transfer membrane (Amersham
Life Science) by capillary transfer in 10i SSC (0n15 M
sodium citrate, 1n5 M NaCl pH 7n0), and baked onto the
membrane at 80 mC, ambient pressure for 2 h. The blot was
prehybridized and then hybridized with probe at 60 mC
overnight in 6i SSC containing 0n1% (w\v) SDS and
sheared denatured calf thymus DNA (100 g ml-"). The blot
was washed at 60 mC in 1n0i SSC, 0n5% SDS and then
washed repeatedly at 50 mC in 0n1i SSC, 0n5% SDS prior to
autoradiography.
RESULTS
Phylogenetic analysis of 16S rRNA revealed nine
groups in two lineages in the Chlamydiaceae
Ninety-three 16S rRNA sequences available from the
Chlamydiaceae, `Candidatus Parachlamydia' and
`Simkania' in GenBank, as of March 1998, were
aligned with new data for SFPD and for WSU 86-
1044. The alignment required few gaps, so no positions
needed to be removed from the analysis. This large
dataset contained a number of clusters of sequences
that were so closely related as to be nearly identical.
Phylogenetic trees were constructed using a subset of
23 of the 93 sequences, chosen so that all clusters were
represented but so that nearly identical sequences were
removed. Parsimony, maximum-likelihood (MLE)
and neighbour-joining (NJ) algorithms were used to
determine phylogenetic relationships among the 23
sequences.
Parsimony analysis found 28 different mostparsimonious
trees, each requiring 693 nucleotide
substitutions. Only 272 of these substitutions were
within the Chlamydiaceae lineage. A consensus tree
was constructed using a 50% majority rule. This tree
had a consistency index of 0n75 (1n0 being the highest
possible), indicating a lack of resolution at several
nodes. Elimination of the outgroups resulted in 26
equally parsimonious trees and only increased the
consistency index to 0n77, indicating that the distance
of the outgroups was not responsible for there being
more than one most parsimonious tree. The low
consistency index was also not due to mutational
saturation, because a plot of pairwise versus phyletic
differences for all groups was linear. The MLE and NJ
trees were similar to several of the parsimony trees, the
differences being at nodes that were poorly resolved in
the parsimony analysis. In particular, the NJ tree had
a monophyletic clade containing feline, abortion,
avian and C. pecorum clusters. This clade shared a
common ancestor with C. pneumoniae, while the
parsimony and MLE trees had C. pecorum paired with
C. pneumoniae. The finding of more than one most
parsimonious tree was due primarily to the presence of
several nodes that were determined by a small number
of nucleotide substitutions.
The MLE, NJ and parsimony trees were all in
agreement with two observations: the same nine
sequence clusters were always present in every tree and
the C. trachomatis-like clusters were separated into a
distinct, well-supported lineage. Eight of the nine
specific clusters were the human strains of C. trachomatis,
swine strains of C. trachomatis, C. trachomatis
strains that infect Muridae species, C. pneumoniae
strains, C. pecorum strains, feline strains, abortion
strains and avian strains. The ninth, guinea pig strain
GPIC, was the single representative of its group. The
order in which GPIC diverged from the feline, abortion
and C. psittaci clusters was unresolved. The parsimony
and NJ trees showed GPIC diverging between the
feline cluster and C. psittaci, while the MLE tree made
GPIC a sister group with the abortion cluster.
Bootstrap analysis, in which 1000 replicate trees were
produced using random subsamples of the nucleotide
positions in the dataset, was used to assess statistical
support for the individual branches (Fig. 1). In the
non-C. trachomatis-like group, the B577 and EBA
abortion strains were always grouped together,
although they formed a monophyletic clade distinct
from the avian cluster in only 55% of the bootstrap
replicates. Thus, the abortion strains were closely
related to each other but as a group had not yet
diverged very far from the avian strains. A clade that
contained feline, guinea pig, avian and abortion
clusters was present in 98% of the trees. The bootstrap
procedure provided 99% support for the monophyly
of the C. trachomatis-like clusters, but little support for
any particular order of divergence among the human,
swine and Muridae clusters within C. trachomatis.
Sixty-eight per cent of the bootstrap replicates showed
International Journal of Systematic Bacteriology 49 419
K. D. E. Everett, R. M. Bush and A. A. Andersen
50 nt
55
66
98
68 100
100
100
100
86
98
99 100
100
93
Simkania negevensis ZT
Parachlamydia acanthamoebae Bn9T
WSU 86­1044
Chlamydia muridarum SFPD
Chlamydia muridarum MoPnT
Chlamydia suis S45T
Chlamydia suis R22
Chlamydia trachomatis L2/434/BU
Chlamydia trachomatis D/UW-3/CX
Chlamydia trachomatis B/TW-5/OT
Chlamydia trachomatis A/Har-13T
Chlamydophila pecorum E58T
Chlamydophila pecorum IPA
Chlamydophila pneumoniae TW-183T
Chlamydophila pneumoniae N16
Chlamydophila felis FP BakerT
Chlamydophila felis FP Cello
Chlamydophila caviae GPICT
Chlamydophila psittaci NJ1
Chlamydophila psittaci MN
Chlamydophila psittaci 6BCT
Chlamydophila abortus B577T
Chlamydophila abortus EBA
VR 656T
VR 125T
VR 122
VR 813T
VR 120T
VR 2282T
VR 628T
VR 629
VR 571BT
VR 885
VR 902B
VR 1474T
VR 123T
VR 1470
VR 1476T
VR 1471T
(U73108)
(AB001783, D85709)
(AB001778, M13769)
(AB001784, U68453)
(AB001817, U68419)
(D85708)
(D85701)
(D85706)
(U73784, U68426)
(Z49873, U76711)
(U73785, D88317)
(D85716)
(D89067, U68438)
(D85719)
(D85721)
(M59178)
(U73109)
(U73110)
(D85718)
(M83313, U68437)
(AF042496)
(Y07556)
(L27666)
.................................................................................................................................................................................................................................................................................................................
Fig. 1. Phylogeny of the order Chlamydiales, constructed using full-length 16S rRNA genes. Branch lengths are measured
in nucleotide substitutions. Numbers show the percentage of times each branch was found in 1000 bootstrap replicates.
Branches without bootstrap values occurred in less than 50% of the trees. Values in parentheses are the GenBank
sequence accession numbers.
Table 2. Percentage differences among the 16S rRNA genes of Chlamydiales spp. type strains and some of their closest
relatives
.................................................................................................................................................................................................................................................................................................................
Chlamydia type strains are MoPnT, A\Har-13T and S45T. Chlamydophila type strains are B577T, 6BCT, GPICT, FP BakerT, E58T
and TW-183T. A consensus sequence (Ccon) was derived from these genes to identify a reference strain that contained the highest
proportion of conserved 16S sequence motifs for the family Chlamydiaceae. Ccon is heavily weighted toward the Chlamydiaceae
lineage because plurality for the consensus was 6, and all nine Chlamydiaceae type strains were included in the identification of
Ccon. Percentages are to the nearest whole integer (p0n5%) or to the nearest decimal (p0n05%) (Jukes & Cantor, 1969).
17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2
1 Ccon 1n9 2n0 2n0 2n4 3n2 4n2 3n1 3n7 4n2 13n0 16n2 16n3 30n9 31n2 33n3 33n4
2 Planctomycetes staleyi 36 35 36 36 35 35 35 35 34 33 37 35 37 35 15 0
3 Pirellula marina 36 35 36 36 35 35 35 35 35 34 37 35 39 33 0
4 Verrucomicrobium VeGlc2 33 33 33 33 33 33 33 33 33 31 33 33 37 0
5 Chloroplast Chlorella ellipsoidea 32 32 32 33 32 32 32 31 31 34 35 35 0
6 Simkania 18 18 18 18 18 18 18 18 18 13 18 0
7 WSU 86-1044 18 18 18 18 18 18 18 18 18 14 0
8 Parachlamydia 15 15 14 15 14 14 14 15 14 0
9 S45T 6 6 6 6 5 7 2 3 0
10 A\Har-13T 5 5 5 5 5 6 2 0
11 MoPnT 4 4 4 5 5 6 0
12 TW-183T 4 4 5 5 4 0
13 E58T 4 4 4 4 0
14 FP BakerT 2 2 2 0
15 GPICT 1 1 0
16 6BCT 0n2 0
17 B577T 0
Accession no. D85709 M13769 D85708 D85701 D88317 L06108 D85718 D89067 U73110 Y07556 AF042496 L27666 X12742 X99390 X62912 M34126
the Chlamydiaceae splitting at its base into two
monophyletic clades: the C. trachomatis-like group
and a clade containing the rest of the Chlamydiaceae
clusters. This pattern represents the most probable
structure for the root of the Chlamydiaceae because the
next most likely split, between C. pneumoniae and all
other Chlamydiaceae, had only 31% bootstrap support.
The clade containing just C. pecorum and C.
pneumoniae in the Fig. 1 bootstrap tree, which also
appeared in the MLE tree, had only 44% support. It
was not conclusive whether C. pecorum, C. pneumoniae
or their common ancestor, diverged first from the C.
trachomatis-like group. The order of divergence at the
base of the Chlamydiaceae tree was most likely the C.
trachomatis-like clusters first, then C. pneumoniae and
C. pecorum groups followed by the feline, guinea pig,
avian and abortion groups.
The non-C. trachomatis-like 16S rRNA gene sequences
varied 5% among themselves. The C. trachomatis-
420 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
Table 3. Percentage differences among 23S rRNA genes of Chlamydiales spp. strains and some of their closest relatives
.................................................................................................................................................................................................................................................................................................................
Percentages are to the nearest whole integer (p0n5%) or to the nearest decimal (p0n01%) (Jukes & Cantor, 1969). MoPn and
SFPD are 0n03% different and have identical percentage differences with all strains as shown. NJ1 and 6BCT are 0n37% different
and have identical percentage differences with all Chlamydiaceae strains as shown.
13 12 11 10 9 8 7 6 5 4 3 2 1
1 Chloroplast Chlorella ellipsoidea 48 48 47 48 48 47 48 48 49 48 48 49 0
2 Simkania 18 18 19 19 20 19 18 18 19 15 18 0
3 WSU 86-1044 19 19 19 19 19 19 18 19 18 15 0
4 Parachlamydia 17 17 18 18 19 18 17 18 18 0
5 R22 8 8 8 8 9 8 2 2 0
6 L2\434\BU 8 8 8 8 9 8 2 0
7 MoPnT 7 7 7 8 8 7 0
8 TW-183T 3 3 3 3 4 0
9 IPA 4 4 5 5 0
10 FP BakerT 2 2 2 0
11 GPICT 2 2 0
12 6BCT 0n7 0
13 EBA 0
Accession no. U76710 U68447 U68451 U68457 U68434 U76711 U68436 U68443 U68420 Y07555 AF042496 U68460 M36158
50 nt
78
99
97
43
100
100
100
100
56
100
Simkania negevensis ZT
Parachlamydia acanthamoebae Bn9T
WSU 86­1044
Chlamydia muridarum SFPD
Chlamydia muridarum MoPnT
Chlamydia suis R22
Chlamydia trachomatis L2/434/BU
Chlamydophila pecorum IPA
Chlamydophila pneumoniae TW-183T
Chlamydophila felis FP BakerT
Chlamydophila caviae GPICT
Chlamydophila psittaci 6BCT
Chlamydophila abortus EBA
(U68419)Chlamydophila psittaci NJ1
(U68447)
(U68451)
(U68457)
(U76711)
(U68434)
(U68443)
(U68420)
(U68436)
(U68437)
(AF042496)
(Y07555)
(U68460)
(U76710)
.................................................................................................................................................................................................................................................................................................................
Fig. 2. Phylogeny of 14 members of the order Chlamydiales, constructed using full-length 23S rRNA genes. Branch
lengths are measured in nucleotide substitutions. Numbers show the percentage of times each branch was found in 1000
bootstrap replicates. Branches without bootstrap values occurred in less than 50% of the trees. Values in parentheses are
the GenBank sequence accession numbers.
like gene sequences varied 3% among themselves
(Table 2). The non-C. trachomatis-like gene sequences
were 4­7% different from the C. trachomatis-like
genes. The 4­7% differences were comparable to 16S
rRNA differences that separate a number of bacterial
species and genera, as determined by BLAST searching
of the GenBank database, and approached neither the
near-zero difference limit for species discussed by Palys
et al. (1997) nor the 80% identity limit proposed for
the class Actinobacteria by Stackebrandt et al. (1997).
The separation of these nine groups was also consistent
with the phyletic separation of chlamydiae based on
this gene (Fig. 1) and with biochemical and phenotypic
differences between the groups. Thus, genetic
differences in the 16S rRNA gene supported the
proposed revision of species and genera in the
Chlamydiaceae.
16S reference sequence determined for the
Chlamydiaceae
To identify a 16S rRNA sequence that could be used to
specifically and easily recognize members of the
Chlamydiaceae, a consensus sequence (Ccon) of repInternational
Journal of Systematic Bacteriology 49 421
K. D. E. Everett, R. M. Bush and A. A. Andersen
.................................................................................................................................................................................................................................................................................................................
Fig. 3. 16S rRNA signature sequences for twelve species in the order Chlamydiales. The amplification/sequencing primers,
16SIGF (5h CGGCGTGGATGAGGCAT 3h) and 16SIGR (5h TCAGTCCCAGTGTTGGC 3h) (51 mC annealing temperature), match or
complement the first and last 17 bases in this sequence, respectively. The Chlamydiaceae species lines: all strains in the
species are identical (upper case), are identical and match the consensus line (-), or most but not all strains use the
indicated nucleotide (lower case); n l no consensus for that species; (.) l alignment gap. Consensus line: all known
Chlamydiaceae are identical (upper case), at least one strain of the Chlamydiaceae is not identical to the consensus
nucleotide (lower case), or fewer than six species have the same base at this position (-). The number of strains used to
compile the consensus for each species is appended to the end of the first lines of sequence. Base 40 is the position 40 in
the 16S rRNA gene of Chlamydiales and also E. coli. The percentage variation within each species signature is appended
to the ends of the last lines of sequence. Dots were inserted into the sequences to improve alignment.
resentative 16S rRNA genes from diverse Chlamydia
strains and from closely related bacteria was identified.
The Ccon sequence represented a plurality 6
identities at each position and matched the most
conserved sequence data among these bacteria. A
percentage difference analysis of Ccon with these
groups was also carried out (Table 2). This comparison
indicated that the 16S rRNA sequence from C. psittaci
B577 best matched a consensus of conserved
Chlamydia sequences.
Phylogenetic analysis of 23S rRNA revealed two
major lineages within the Chlamydiaceae
Thirteen complete Chlamydiales 23S rRNA gene
sequences, including 11 Chlamydia strains, `Simkania'
Z and WSU 86-1044, were sequenced and compared to
the previously reported 23S rRNA sequence of
`Candidatus Parachlamydia' (Amann et al., 1997). The
Chlamydia sequences differed from the outgroup
sequences by 15­20% (Table 3). Parsimony analysis
produced a single most parsimonious tree with 1380
nucleotide substitutions and a consistency index of
0n76 (Fig. 2). The MLE tree was identical to the
parsimony tree and C. pecorum and C. pneumoniae
were paired together. The NJ tree differed from this
tree only in that it showed C. pecorum strain IPA to be
more closely related to the outgroups than was C.
pneumoniae TW-183.
The Chlamydiaceae 23S rRNA tree split at its base into
two monophyletic lineages with 100% bootstrap
support (Fig. 2). One lineage included the C.
trachomatis-like strains and the other included the
non-C. trachomatis-like strains. Among the C.
trachomatis-like strains, the swine and human isolates
separated from the Muridae isolates with almost 100%
bootstrap support. The base of the non-C. trachomatis-
422 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
like lineage was not well-defined: either C. pneumoniae
or a common ancestor of C. pneumoniae and of C.
pecorum could have been most closely related to the C.
trachomatis-like clade. A monophyletic lineage containing
the C. psittaci abortion\avian\feline\guinea
pig strains formed the rest of the non-C. trachomatislike
clade with 100% bootstrap support. A saturation
plot of pairwise versus phyletic differences did not
show evidence of mutational saturation; thus the low
consistency index was due not to excessive homoplasy
but to a lack of information needed to resolve some
specific nodes (e.g. the C. pneumoniae j C. pecorum
node and the WSU 86-1044 j `Candidatus Parachlamydia'
node).
The non-C. trachomatis-like 23S rRNA gene sequences
varied 5% among themselves; the C. trachomatislike
23S rRNA gene sequences varied 2% among
themselves (Table 3). The non-C. trachomatis-like gene
sequences were 7­9% different from the C.
trachomatis-like genes. The 7­9% gene sequence
differences were comparable to 23S rRNA differences
that separate a number of bacterial genera, as determined
by BLAST searching of the GenBank database.
They were also consistent with the phyletic separation
of groups in the Chlamydiaceae (Figs 1 and 2) and with
biochemical and phenotypic differences between the
groups. Thus, genetic differences in the 23S rRNA
gene supported the proposed revision of species and
genera in the Chlamydiaceae.
Sequence signatures identified for the
Chlamydiaceae groups
Previously it was shown by sequence comparison that
the 16S­23S ribosomal intergenic spacer is a defined
region of sequence that is functionally conserved and
distinctive for each of the nine chlamydial groups
(Everett & Andersen, 1997). A `signature sequence'
such as this can identify these groups for purposes of
classification. Signature sequences were identified in
the 16S and 23S rRNA genes of the Chlamydiaceae by
aligning all of the ribosomal segments for chlamydial
organisms that are in GenBank. The 16S signature
sequence started at base 40 in the gene and was 298
bases long (Fig. 3). The homologous `Simkania',
`Candidatus Parachlamydia' and WSU 86-1044
sequences were also examined (Fig. 3). Confidence in
the 16S species signature was highest for human C.
trachomatis strains, C. pneumoniae strains, C. pecorum
strains, and C. psittaci feline, abortion and avian
strains because 4 sequences were available for each.
Variation within the 16S signature consensus for any
single species was 3%. New data from 16S signature
sequence analysis of C. pneumoniae N16 and C.
trachomatis SFPD were used to update N16 and SFPD
sequences in GenBank and in Fig. 3.
The 23S signature sequence, which was domain I of
this gene, started at base 1 in the gene and was 627
bases long (Fig. 4). The homologous `Simkania' and
`Candidatus Parachlamydia' sequences were also
examined (Fig. 4). Confidence in the 23S species
signature was highest for human C. trachomatis
strains, swine C. trachomatis-like strains, C.
pneumoniae strains, C. pecorum strains and C. psittaci
abortion and avian strains, because 5 sequences
were available for each. Variation within the domain I
signature consensus for any single species was always
3%, but usually 1% (Fig. 4).
PFGE revealed conserved genome size in the
Chlamydiaceae
PFGE of agarose-embedded chlamydial DNA was
employed to determine genome sizes for six groups in
Chlamydia and to compare these sizes with `Simkania'
and E. coli. The data indicated that uncut chlamydial
genome migrates at an approximate size of 1­1n2 Mbp
(Fig. 5). C. trachomatis strains and C. trachomatis-like
swine strains had an apparent size of 1­1n1 Mbp and
non-C. trachomatis strains had an apparent size of
about 1n2 Mbp. This agreed with the size of the
1n045 Mbp C. trachomatis strain L2\434\BU genome
identified by Birkelund & Stephens (1992). Additional
study of these genomes using restriction endonucleases
will be needed to confirm the actual genome sizes.
Extrachromosomal plasmids were strain- and group-
specific
To compile information that could contribute to a
more complete description of groups in the
Chlamydiaceae, chlamydial DNA was examined for
the presence of an extrachromosomal plasmid. DNAs
that had been prepared in agarose plugs for PFGE
were separated by standard electrophoresis on 1%
gels, were examined by ethidium bromide staining, and
were Southern blotted using a probe that matched the
plasmid origin of replication. A sharp band that
stained only weakly with ethidium bromide hybridized
strongly to the probe. The mobility of this band was
markedly slower than the mobility of a band of sheared
DNA that stained strongly with ethidium bromide.
There was no hybridization of the probe to the sheared
DNA. These bands were larger than the 12 kbp DNA
molecular size marker. A faint band with a mobility of
7n5 kbp was only rarely detected with the probe on
Southern blot. Handling of the chromosomal\plasmid
preparations in liquid form (rather than in agarose
plugs) greatly increased the amount of 7n5 kbp plasmid
detected by Southern blot and reduced the amount of
detectable 12 kbp plasmid. The retarded mobility of
the 12 kbp plasmid band was consistent with this
band being an open circular form of the chlamydial
plasmid (Levene & Zimm, 1987) or with its being a
dimer of interlinked circular forms, as have been
previously reported.
The presence of plasmids was determined or confirmed
in 14 strains (Table 4). The absence of plasmid was
discovered or confirmed for six strains (Table 4).
Strains were designated plasmid- only if a genomic
International Journal of Systematic Bacteriology 49 423
K. D. E. Everett, R. M. Bush and A. A. Andersen
(a)
.................................................................................................................................................................................................................................................................................................................
Fig. 4. For legend see facing page.
424 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
(b)
1 kb
Primer 16SF2
Primer
IGSIGF
Primer
U23F Primer 23R Primer 23SIGR
BbrPI
Domain I signature sequence (627 b)
23S rRNA geneIntergenic spacer16S rRNA gene
.................................................................................................................................................................................................................................................................................................................
Fig. 4. 23S domain I rRNA signature sequences for eleven species in the order Chlamydiales. This segment could be PCR
amplified using an annealing temperature of 61 mC and amplification/sequencing primers U23F (5h
GATGCCTTGGCATTGATAGGCGATGAAGGA 3h) (bases 31­60) and 23SIGR (5h TGGCTCATCATGCAAAAGGCA 3h) (extending
13 bases past base 627). (a) Chlamydiaceae species lines: all strains in the species are identical (upper case), are identical
and match the consensus line (-), or most but not all strains use the indicated nucleotide (lower case); (.) l alignment
gap. Consensus line: all known Chlamydiaceae are identical (upper case), at least one strain of the Chlamydiaceae is not
identical to the consensus nucleotide (lower case), or fewer than six species have the same base at this position (-). The
number of strains used to compile the consensus for each species is appended to the end of the first lines of sequence.
Base 1 is the first nucleotide of the 23S rRNA gene, based on primer extension analysis (Everett & Andersen, 1997). The
percentage variation within each species signature is appended to the ends of the last lines of sequence. Dots were
inserted into the sequences to improve alignment. (b) Map of the domain I signature sequence in the 23S rRNA gene.
Primers 16SF2, U23F and 23SIGR recognize all members of the Chlamydiales. Primers IGSIGF and 23R are specific for the
Chlamydiaceae.
FPVaccine
H7
R22
EBA
OSP
B577T
PFGEII
6BCT
VR122
MNZhang
CP3
GD
NJ1
WC
MoPnT
A/Har-13T
B/TW-5/OT
D/UW-3/CX
F/IC/CAL3
L2/434/BU
E.coliJM109
PFGEII
22
16
11
092
085
077
061
045
009
Mbp
Chlamydiatrachomatis
Chlamydiamuridarum
Chlamydophilapsittaci
Chlamydophilaabortus
Chlamydiasuis
Chlamydophilafelis
.....................................................................................................
Fig. 5. PFGE of chlamydial chromosomes.
Linearized chromosomes migrated at 1n0­
1n2 Mbp. E. coli JM109 chromosome was
included as a control.
International Journal of Systematic Bacteriology 49 425
K. D. E. Everett, R. M. Bush and A. A. Andersen
Table 4. Presence or absence of exrachromosomal plasmid in selected strains of Chlamydia and Chlamydophila spp.
.................................................................................................................................................................................................................................................................................................................
Compiled from Farencena et al. (1997); Girjes et al. (1988); Grayston et al. (1989); Joseph et al. (1986); Lusher et al. (1989);
Peterson et al. (1990); Thomas et al. (1997); and Timms et al. (1988). Strains in bold were identified or confirmed in this study.
Species Present Absent
Chlamydia trachomatis A/Har-13T
, D/UW-3/CX, B/TW-5/OT, L2 (pCT-); Ba (pCT-); GTS-3, GTS- 10,
F/IC/CAL3, L1\440\LN, L2\434\BU GTS-17, GTS-18,GTS-21, GTS-23,
GTS-31, GTS-36, GTS-39*
Chlamydia suis S45T
, R22, R24, R27, H7 Chlamydia
muridarum MoPnT
Chlamydophila
caviae GPICT Chlamydophila
felis Cello, Pring FP BakerT
, FP Vaccine
Chlamydophila psittaci 6BCT
, A24, M56, MN Zhang, N352, MN VR-122
RA1\56 gull, 360 duck
Chlamydophila abortus ­ B577T
, EBA, OSP, A22, S26,
Chlamydophila pneumoniae N16 TW-183T
, Koala I, IOL-207
Chlamydophila pecorum E58T
, Koala II *
Forty University of Massachusetts Medical Center Chlamydia trachomatis isolates from sexually transmitted disease (STD) or pelvic
inflammatory disease (ID) patients were grown and characterized; nine were plasmid minus (An & Olive, 1994; An et al., 1992).
 A. Rodolakis, personal communication.
Table 5. Taxa in the order Chlamydiales
.....................................................................................................................................................................................................................................
Source information is provided where possible. Biovar reference strains may be obtained from
ATCC or from the original sources.
Taxon Type/reference strain
Name ATCC no.
Family I: Chlamydiaceae
Chlamydia muridarum sp. nov. MoPnT VR 123T
Chlamydia suis sp. nov. S45T VR 1474T
Chlamydia trachomatis A\Har-13T VR 571BT
Biovar trachoma C\PK-2
Biovar LGV L2\434\BU VR 902B
Chlamydophila abortus sp. nov. B577T VR 656T
Chlamydophila caviae sp. nov. GPICT VR 813T
Chlamydophila felis sp. nov. FP BakerT VR 120T
Chlamydophila pecorum comb. nov. E58T VR 628T
Chlamydophila pneumoniae comb. nov. TW-183T* VR 2282T
Biovar TWAR TW-183 VR 2282
Biovar Koala LPCon
Biovar Equine N16
Chlamydophila psittaci comb. nov. 6BCT VR 125T
Family II: Simkaniaceae fam. nov.
Simkania negevensis sp. nov. ZT VR 1471T
Family III: Parachlamydiaceae fam. nov.
Parachlamydia acanthamoebae sp. nov. Bn
*
T VR 1476T
Family IV: WSU 86-1044 VR 1470
* TW-183T is also available through the Washington Research Foundation, 1107 NE 45th St, Suite
205, Seattle, WA 98105, USA (Tel: j1 206 633 3569; Fax: j1 206 633 2981; WWW URL:
http:\\www.halcyon.com\lori\wrf.htm).
426 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
band was detected by PFGE and no plasmids were
detected by Southern blot analysis.
DISCUSSION
Identification of coherent groupings in Chlamydiales:
ribosomal evidence
We propose a reclassification of groups in the order
Chlamydiales based on 16S rRNA sequence similarity
clusters, on concurrence between analyses of fulllength
16S and 23S rDNA data for all known groups,
and on supporting evidence showing these groups to
be phenotypically and ecologically differentiated
(Palys et al., 1997). Some of these groups are wellcharacterized
(see descriptions, below), while others
have only recently been identified and phenotypic
studies are under way. Ecological differentiation of
groups is evident by the often host-related variations in
virulence, morphology, propagation and chronic
maintenance. According to this proposal, members of
the order Chlamydiales are obligately intracellular
bacteria that have the chlamydia-like developmental
cycle of replication and that have 80% rDNA
sequence identity with chlamydial 16S rRNA genes
and\or 23S rRNA genes (Figs 1 and 2, Tables 2 and 3).
This order includes strains belonging to the
Chlamydiaceae, strains closely related to `Candidatus
Parachlamydia acanthamoebae', `Simkania' strain Z
and strain WSU 86-1044. This proposal separates
these groups at the family level. Actual rRNA gene
differences between these groups were 13­20%, and
between other bacterial lineages this range of
differences can typically separate classes, orders or
families. The Chlamydiaceae is a well-characterized
family and all strains have 90% rRNA identity.
Among 16S rRNA sequences in the Chlamydiaceae,
strain B577 has diverged less than all others from
`Ccon', a chlamydial consensus sequence (Table 2).
Therefore, to be identified as a member of the
Chlamydiaceae, the 16S rRNA gene of a new
chlamydia-like isolate should have 90% identity
with the 16S rRNA gene of B577 (accession no.
D85709).
Analysis of the rooted, 1558 nt 16S rRNA dataset
supported two specific conclusions. The first major
conclusion was that nine sequence clusters were present
in the Chlamydiaceae. These clusters were present
in all phylogenetic trees and were independent of the
algorithms used to construct the trees. These groupings
agreed with many phenotypic and ecological
differences among chlamydial groups, including antigenicity,
associated disease, host range and genomic
endonuclease restriction (Everett & Andersen, 1997).
They were also in agreement with observations by
Herring (1993) that these groupings would provide an
`outline for a new taxonomy of chlamydial species'.
Genetic studies of the Chlamydiaceae have shown
patterns of relatedness that were consistent with these
clusters (Carter et al., 1991; Everett & Andersen, 1997;
Fitch et al., 1993; Glassick et al., 1996; Kaltenboeck et
al., 1993; Lo$ bau et al., 1995; Pettersson et al., 1997;
Pudjiatmoko et al., 1997; Storey et al., 1993;
Takahashi et al., 1997; Zhang et al., 1993). The 16S
rRNA tree failed to show strong genetic divergence
between the EBA\B577 abortion cluster and the avian
cluster, from which the abortion group is evolving.
However, the abortion cluster was well-supported by
DNA­DNA reassociation (Table 1), by the intriguing
absence of plasmids from all known isolates (Table 4)
and by virulence studies (Jorgensen, 1997; Page, 1967;
Rodolakis et al., 1989).
The second major conclusion derived from the 16S
rRNA analysis was that the C. trachomatis-like group
diverged before other groups in the Chlamydiaceae.
There was 99% support for the monophyly of the C.
trachomatis-like group and 68% support for the early
divergence of this group (Fig. 1). This conclusion was
possible because of the unambiguous rooting provided
by the `Candidatus Parachlamydia', `Simkania' and
WSU 86-1044 genes. Problems in rooting the
Chlamydiaceae and in determining relationships within
the Chlamydiaceae have been ongoing since 1986,
when ribosomal data were first obtained for
chlamydiae (Weisburg et al., 1986). Most recently,
Pettersson et al. (1997) used eight ribosomal sequences
from `Simkania', `Candidatus Parachlamydia' and
more distantly related bacteria to root a set of nine
chlamydial sequences. However, because of difficulty
in aligning the chlamydial sequences to the distant
outgroups, 22% of the 16S rRNA sequence positions
contained gaps and on this basis were removed from
their analysis. Their resulting phylogeny had little
support in our analyses, which used complete gene
sequences.
Analysis of the 23S rRNA showed 100% support for
the early divergence of C. trachomatis-like strains in
the Chlamydiaceae (Fig. 2). The 23S rRNA phylogeny
was in complete agreement with the most probable 16S
rRNA phylogeny. Separation of lineages was greatest
and bootstrap support was strongest, using the 23S
rRNA data.
Evolution of coherent clusters in Chlamydiales
Recent discoveries of chlamydiae in amoebae (Amann
et al., 1997; Birtles et al., 1997; Gautom et al., 1996)
suggest the possibility that chlamydial parasites
radiated from single-celled eukaryotes into multicelled
hosts. This radiation would have been accompanied by
intense selective pressure in animal hosts. This selective
pressure may have influenced the evolution of all of the
proposed groupings in Chlamydiales, because
members of all of the families have been associated
with infection of vertebrates (Birtles et al., 1997;
Dilbeck et al., 1990; Kahane et al., 1999; Moulder,
1991). Intense selective pressure is consistent with the
large differences seen between the rRNAs of the
proposed families. Between some Chlamydiaceae
groups, however, branching order was affected by
relatively small numbers of nucleotide substitutions in
International Journal of Systematic Bacteriology 49 427
K. D. E. Everett, R. M. Bush and A. A. Andersen
the rRNA, although there were large DNA­DNA
reassociation differences (Table 1). (In Figs 1 and 2
such branches had the weakest bootstrap support or
the branching orders were shown as unresolved.) This
suggests that intense selective pressures did not always
involve the rRNA. An unusually low rate of rDNA
change could very likely be due to the inability of the
replicating chlamydiae to survive the extracellular
environment or to infect new host cells. Propagation of
changes in rRNA sequence and in ribosome function
can take place in chlamydiae only if mutants remain in
step with the replication cycle of the total population
in the inclusion; other mutants may not survive host
cell lysis or may not be able to compete successfully for
new host cells in chronically infected hosts.
Evidence for the early divergence of the
C. trachomatis-like group
The strong ribosomal evidence for early divergence of
the monophyletic C. trachomatis-like group in the
Chlamydiaceae was supported by other data: genome
size (Fig. 5), glycogen production only by the C.
trachomatis-like strains (Moulder, 1991; Rogers et al.,
1996), ompA sequence analysis (Kaltenboeck et al.,
1993), and conservation of epitopes deduced from the
ompA sequences of C. trachomatis-like strains (see
descriptions below). Genome size among the C.
trachomatis-like strains was smaller than among the
non-C. trachomatis-like strains (Fig. 5). These sizes
were consistent with recent determinations of genome
size for specific isolates: the 1n2 Mbp size seen in Fig. 5
for non-C. trachomatis-like strains was close to the
1230025 bp genome size of C. pneumoniae (GENSET,
1997). The 1n1 Mbp size for C. trachomatis L2\434\BU
and D\UW-3\CX in Fig. 5 corresponded to a mapped
size of 1n045 Mbp (Birkelund & Stephens, 1992) and
to genome sizes of 1038680 bp (GENSET, 1997)
and 1042519 bp (Stephens et al., 1998), respectively.
Glycogen production by bacteria has been shown to be
correlated with the management of nutrient deprivation
(Sakamoto & Bryant, 1998). Thus, it is possible
that a gene which was normally essential during
nutrient deprivation was lost by genetic deletion in the
formation of the C. trachomatis-like lineage.
Evidence for ecologically coherent clusters
At least two of the proposed families have evolved
specific ecological niches: the Chlamydiaceae are primarily
vertebrate pathogens and strains in the
`Candidatus Parachlamydia' group appear to reside
primarily in amoebae. Ecologically coherent clusters
can be identified by DNA­DNA reassociation (Palys
et al., 1997). DNA­DNA reassociation analysis of the
Chlamydiaceae showed groupings that were congruent
with the nine groups identified using 16S and 23S
rRNA data (Table 1). The range of DNA­DNA
reassociation similarity among the groups in the
Chlamydiaceae was 1­100%. Within C. pecorum and
C. pneumoniae the ranges were 88­100%. In the
current C. psittaci, however, the range was much
broader (20­85%) because it contained four of the
groups separated by ribosomal clustering. The two C.
trachomatis-like groups that have been characterized
were 20­65% similar by DNA­DNA reassociation.
Both the C. psittaci and the C. trachomatis ranges were
sufficiently broad that they could each encompass new
species: the value established for the discrimination of
species is 70% and for the discrimination of genera
is about 20% (Amann et al., 1995; Schleifer &
Stackebrandt, 1983; Wayne et al., 1987). Therefore,
DNA­DNA reassociation provided good evidence
that the ribosomal clusters were ecologically distinct
groups.
DNA­DNA reassociation is a difficult technique to
apply to the measurement of relatedness among
intracellular bacteria, however. Values are affected not
only by genetic distance but also by the presence of
diverse host DNAs, multicopy extrachromosomal
DNAs (Brenner & Falkow, 1971), strain integrity, and
methodology. Some of these influences are evident in
the available DNA reassociation data for chlamydiae.
For example, C. psittaci B577 has been reported to
have similarities of 34 and 85% versus C. psittaci
6BCT; B577 has reported similarities of 27 and 46%
with C. psittaci Cal-10 MN (Fukushi & Hirai, 1989)
(Table 1). Such wide variances in chlamydial data
indicate that DNA­DNA reassociation is not the
method of choice for conclusively determining
relatedness among chlamydial populations.
Other evidence also contributes to the suggestion that
the Chlamydiaceae is made up of a number of
ecologically distinct populations. An ecologically distinct
population can typically occur when one group
outgrows others in a particular niche. It has been
observed that most chlamydial isolations produce
single serovars, rather than mixed populations and
that most Chlamydia groups have specific host or
disease associations. Thus, apparently, long-term adaptation
between chlamydiae and animal species has
contributed to the evolution of ecologically distinct
populations. The apparent host ranges are fairly
narrow. For example, one group of C. trachomatis-like
chlamydiae has been isolated only from swine, some C.
trachomatis-like strains and the TWAR serovar of C.
pneumoniae are found exclusively in humans. C.
pecorum has been isolated only from mammals. Some
C. psittaci strains are primarily isolated from birds;
one group primarily infects cats. Another group is
associated with colonization of the placenta, abortion
and weak neonates. Disease and host associations
have been used for years to help restrict the probable
identity of chlamydial agents. However, the condition
of the host or the presence of other bacteria or viruses
can also play a role in the severity of chlamydial
disease and may lead to inappropriate conclusions
about the virulence of isolates. In addition, apparently
host-specific strains can be made to cause disease in
experimentally infected animals (Page, 1967) and
428 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
Chlamydia strains that infect birds have caused sporadic
disease in mammals and tortoises. Thus, although
host and disease associations are not definitive markers
for purposes of classification, they are consistent with
the ecological separation of these populations.
Variable traits in Chlamydiaceae
Some data assembled in this study contributed to
descriptions of groups but proved to be inappropriate
for primary group separations. Specifically, these data
included plasmid- and plasmid+ genotypes, which
could be found in most groups (Table 4) and resistance
to sulfadiazine, which interferes with folate synthesis.
Sulfadiazine resistance appears to characterize many
of the lineages in Chlamydiales, although this has not
been widely published. Some strains that are known to
be resistant include C. pecorum IPA and E58T, C.
pneumoniae AR-39, C. psittaci FP Baker, GPIC, VS1,
CP3, MN, B577 (A. A. Andersen, unpublished; B.
Kaltenbo$ ck, unpublished), C. trachomatis-like swine
strains (Andersen & Rogers, 1998) and `Simkania'. C.
trachomatis-like isolates from humans and Muridae
are sensitive to sulfadiazine, however (Fox et al., 1993;
Moulder et al., 1984). Furthermore, both resistance
and sensitivity in apparently isogenic C. psittaci 6BC
strains has been reported (Lin & Moulder, 1966). Fan
et al. (1992) determined that sulfadiazine-resistant and
sulfadiazine-sensitive chlamydiae synthesize folates
but vary in their ability to transport host folates. Fan
et al. (1992) concluded that chlamydial synthesis and
transport of folate is in a transitional stage of evolution
and probably varies from one strain of Chlamydia to
the next. For these reasons, it is inappropriate to use
sulfadiazine resistance as a phyletic marker for
chlamydiae.
The observations described in this report are consistent
with the presence of two genera and nine species in the
Chlamydiaceae, as distinguished by genetic, phenotypic
and ecologic differences. We found that ribosomal
sequence data could be used to easily assign
isolates to these groups and to also distinguish families
within the Chlamydiales.
Emended description of the order Chlamydiales
We emend the description of the order Chlamydiales to
include obligately intracellular bacteria that have a
chlamydia-like developmental cycle of replication,
Gram-negative or Gram-positive infectious EBs (elementary
bodies), 80% 16S rRNA gene sequence
identity), and\or 80% 23S rRNA gene sequence
identity with Chlamydiales spp. Currently, the order
Chlamydiales includes the families Chlamydiaceae and
Simkaniaceae, which have Gram-negative EBs, and
Parachlamydiaceae, which has variable Gram staining
of EBs. The EB form has an inner and an outer
membrane and a variable periplasmic space. EBs are
round, highly electron-dense, 0n2­0n6 m in diameter,
and metabolically inactive. The chlamydial cycle of
replication is initiated when EBs are endocytosed by
eukaryotic cells. During this stage, EBs reside within
cytoplasmic inclusions where they differentiate by
enlarging to 0n6­1n5 m, becoming less electron-dense
RBs (reticulate bodies), and undergoing binary fission.
Inclusions are unique vacuoles that do not undergo
acidification or lysosomal fusion. Inclusions that have
been studied in detail do not correspond to canonical
endocytic vesicles, being essentially dissociated from
the endocytic pathway and having some similarities
with recycling endosomes (Hackstadt et al., 1997; van
Ooij et al., 1997; Taraska et al., 1996). Over a period of
days, RBs condense into EBs and chlamydiae are
released by host cell rupture or by fusion of the
inclusion membrane with the host cell plasma membrane.
No alternate host vector is required. Many
species of Chlamydiales coexist in an asymptomatic
state within specific hosts, and it is widely believed that
these hosts provide a natural reservoir for these species.
The type genus for Chlamydiales is Chlamydia.
Emended description of the family Chlamydiaceae
The family Chlamydiaceae was previously described by
Rake (1957). In accordance with rRNA analyses and
corroborating sequence data, the emended family
Chlamydiaceae is divided into two genera. Rules 39a
and 39b of the International Code of Nomenclature of
Bacteria state that when a genus is subdivided, the
original generic name must be retained by the genus
containing the original type species (Lapage et al.,
1992). Therefore, the genus name Chlamydia must
remain with Chlamydia trachomatis, which contains
A\Har-13T, the original type strain. A new name,
Chlamydophila, has been coined for the genus containing
non-Chlamydia trachomatis-like species and
strains.
The family Chlamydiaceae includes current members
of the order Chlamydiales that have 10% overall
16S rRNA gene diversity, 10% overall 23S rRNA
gene diversity, a genome size of 1n0­1n24 Mbp, either
one or two ribosomal operons in each genome, no
tRNA in the 16S­23S intergenic spacer, little or no
muramic acid, and the antigenic LPS trisaccharide
Kdo-(2 8)-Kdo-(2 4)-Kdo. The GjC content
for the Chlamydiaceae spp. is about 40%:
42n7p1n4 mol% according to Moulder et al. (1984)
and 40n5p1n5 mol% according to Cox et al. (1988),
using thermal denaturation methods; 39n5p0n3 mol%
according to Fukushi & Hirai (1992) using an HPLC
method. Among the nearly 100 16S rRNA genes that
have been analysed for the Chlamydiaceae, the gene
from strain B577 is most similar to a consensus
sequence for the family (Table 3). Therefore, to be
identified as a member of the Chlamydiaceae, the 16S
rRNA gene of a new chlamydia-like isolate should
have 90% identity with the 16S rRNA gene of B577
(accession no. D85709). The Chlamydiaceae are Gramnegative.
Host-cell ATP is known to be required by
some strains of C. psittaci and C. trachomatis, and may
possibly be a requirement for all members of this
family. The extracellular osmotic stability of the
International Journal of Systematic Bacteriology 49 429
K. D. E. Everett, R. M. Bush and A. A. Andersen
Chlamydiaceae EBs is maintained by a complex of
disulfide-cross-linked envelope proteins. These include
a major outer-membrane protein (MOMP; translation
product of ompA) with a molecular mass of 40 kDa, a
hydrophilic cysteine-rich 60 kDa protein, and a lowmolecular-mass
cysteine-rich bacterial lipoprotein.
When chlamydiae infect cells, the disulfide cross-links
within and among these envelope proteins become
chemically reduced, allowing transformation of EBs
into RBs. Penicillin binding studies and genetic analyses
indicate that at least some of the genes that are
required for the synthesis of peptidoglycan are present
in the chlamydial genome. However, chlamydiae do
not contain muramic acid, indicating that chlamydial
cell walls do not contain significant amounts of
peptidoglycan. The bright flickering appearance,
varying in intensity and duration, that is seen in
chlamydiae-filled inclusions using visible light microscopy,
suggests some degree of bacterial motility for
strains of C. trachomatis, C. trachomatis-like swine
strains, C. psittaci strains FP Baker, 6BCT, VS1, CP3
and B577, and C. pecorum strain IPA (A. A. Andersen,
unpublished data). Many, but not all, members of the
Chlamydiaceae possess an extrachromosomal plasmid
of about 7n5 kbp (Table 4). These plasmids exhibit
60­80% interspecies conservation of sequence
(Thomas et al., 1997), and shared features suggest that
these plasmids have a monophyletic origin. These
shared features include the conserved organization of
eight open reading frames and an iteron in the origin of
replication, which may regulate plasmid copy number
(Nordstro$ m, 1990; Thomas et al., 1997). The iteron
consists of four highly conserved tandem repeats.
Plasmid copy number in some strains may also be
regulated by antisense RNA (Nordstro$ m, 1990;
Thomas et al., 1997).
The family Chlamydiaceae is distinguished from
Simkaniaceae by 16S rRNA sequence differences
(18n6p0n1%), 23S rRNA sequence differences
(18n6p0n3%), and by the absence of detectable
Chlamydiaceae-specific Kdo trisaccharide antigen in
`Simkania' using a family-specific mAb (Kahane et al.,
1999). The Chlamydiaceae spp. are distinguished from
`Candidatus Parachlamydia' by 16S rRNA sequence
differences (14n9p0n7%), 23S rRNA sequence
differences (17n7p0n5%), and by the variable
responses of `Candidatus Parachlamydia' EBs to
Gram staining (Amann et al., 1997; R. J. Birtles,
personal communication). Members of the
Chlamydiaceae can be readily identified and differentiated
by signature sequence analysis (Figs 3 and 4).
The type genus for the family Chlamydiaceae is
Chlamydia.
Emended description of the genus Chlamydia,
including specific human, hamster, mouse and swine
isolates
The genus Chlamydia previously included all known
chlamydiae (Moulder, 1984). As emended, Chlamydia
is one of two genera in the Chlamydiaceae and includes
Chlamydia trachomatis, Chlamydia muridarum gen.
nov., sp. nov. and Chlamydia suis gen. nov., sp. nov.
The previous species, Chlamydia pecorum, Chlamydia
pneumoniae and Chlamydia psittaci, have been transferred
to the genus Chlamydophila. The complete 16S
and 23S rRNA gene sequences of Chlamydia species
that have thus far been examined are each 97%
identical. To be included in this genus, 16S or 23S
rRNA sequences of new isolates should be 95%
identical to the type strain, A\Har13T. Chlamydia
species are readily identified and distinguished from
other species by signature sequences (Figs 3 and 4) or
by any of several other genes. Glycogen is produced by
Chlamydia species and has been characterized by
Garrett (1975). Glycogen is easily detected in the
human Chlamydia trachomatis serovars and is detectable
to varying degrees in Chlamydia muridarum
and Chlamydia suis. The Chlamydia genomes characterized
thus far are 1n0­1n1 Mbp, somewhat smaller
than Chlamydophila genomes (Fig. 5). Chlamydia
genomes examined thus far have two identical
ribosomal operons (Engel & Ganem, 1987; Everett &
Andersen, 1997; Fukushi & Hirai, 1993; Scieux et al.,
1992). The majority of strains in this genus have
extrachromosomal plasmids, but not all (Table 4).
Chlamydia strains have varying inclusion morphology
and varying sensitivity to sulfadiazine. The currently
known strains in Chlamydia have an epitope in MOMP
that matches the core epitopes NPTI, TLNPTI,
LNPTIA or LNPTI, recognized by vs4 Chlamydia
trachomatis mAbs (see descriptions below) (Batteiger
et al., 1996). The type species for the genus Chlamydia
is Chlamydia trachomatis.
Emended description of Chlamydia trachomatis
Chlamydia trachomatis, as previously described
(Moulder et al., 1984), comprised two human biovars
and a murine biovar. As emended, only strains from
the human biovars of Chlamydia trachomatis are being
retained in Chlamydia trachomatis. Therefore, according
to Rule 40b of the International Code of Nomenclature
of Bacteria, the original Chlamydia
trachomatis epithet is retained by the group of human
strains which contain A\Har13T, the original type
strain (Lapage et al., 1992). As emended, Chlamydia
trachomatis strains have a high degree of sequence
conservation. The Chlamydia trachomatis 16S rRNA
genes that have been sequenced to date differ by
0n65%. Chlamydia species are readily identified and
distinguished from other species by ribosomal signature
sequences (Figs 3 and 4) or by inspection of the
16S­23S intergenic spacer (Everett & Andersen, 1997).
Any of several other gene sequences may also be used
to identify Chlamydia trachomatis. In particular, the
gene for the MOMP, ompA (omp1), is widely used to
distinguish Chlamydia trachomatis strains. Many, but
not all, Chlamydia trachomatis strains have the extrachromosomal
plasmid, pCT (Table 4). Glycogen accumulation
by Chlamydia trachomatis is readily
detected with iodine staining of inclusions. Chlamydia
430 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
trachomatis strains are generally sensitive to
sulfadiazine and tetracyclines. Most strains of
Chlamydia trachomatis are recognized by mAbs to vs4
core epitopes NPTI, TLNPTI, LNPTIA and LNPTI
in MOMP (Batteiger et al., 1996; Peterson et al., 1991).
Chlamydia trachomatis causes trachoma, sexually
transmitted disease, some forms of arthritis, and
neonatal inclusion conjunctivitis and pneumonia. The
type strain for Chlamydia trachomatis is A\Har-13T
(l ATCC VR 571BT).
The 18 serovars of Chlamydia trachomatis are clustered
into two biovars: trachoma and lymphogranuloma
venereum (LGV) (Batteiger, 1996; Moulder et al.,
1984). These serovars are recognized by specific mAbs
and can be distinguished by ompA sequence
differences. Worldwide, each serovar has only a minor
amount of diversity, according to ompA sequence
analysis. The trachoma biovar currently has 14
serovars designated by the letters A through K, plus
Ba, Da and Ia. Infection is limited primarily to
squamocolumnar cells of mucous membranes.
Serovars A­C are primarily associated with endemic
trachoma and serovars D­K with sexually transmitted
infection. The LGV biovar consists of four serovars,
L1, L2, L2a and L3. LGV serovars are sexually
transmitted and can invade lymphatic tissue. There is a
clear separation of these biovars based on pathogenicity
and on growth in cell culture and in laboratory
animals. However, there is not a clear molecular
pattern of separation of the LGV biovar from the
trachoma biovar. Antigenic analyses of MOMP and
sequence analyses of the ompA gene that expresses
MOMP suggest that L1 and L2 are closely related to
the B- and E- trachoma serovars and that L3 is related
to the A-, C- and H-trachoma serovars (Fitch et al.,
1993). Analyses of the extrachromosomal plasmid and
of the gene for the 60 kDa cysteine-rich protein,
however, indicate that the LGV serovars are similar
and that they differ from serovar B. The 16S rRNA
sequences of serovars A, B and D are closer to each
other than they are to the serovar L2 sequence. The
kdtA sequences in the trachoma biovar, including
serovars A, B, Ba, D and E, are also phyletically closer
than they are to L2 kdtA. The groEL sequence of L2 is
phyletically almost as different from the serovar A
groEL as it is from Chlamydia muridarum MoPn
groEL. It would be inappropriate, therefore, to attempt
to further separate the LGV biovar and the
trachoma biovar using molecular criteria at the present
time. The reference strain for the LGV biovar is
L2\434\BU (ATCC VR 902B). The reference strain
for the trachoma biovar is C\PK-2.
Description of Chlamydia muridarum sp. nov.,
including hamster and mouse isolates previously
belonging to Chlamydia trachomatis
Chlamydia muridarum [mu.ri.dahrum. M.L. pl. gen.
fem. n. muridarum of the Muridae (i.e. the mouse\
hamster family)].
Two strains of Chlamydia muridarum, MoPn and
SFPD (Fox et al., 1993; Nigg, 1942; Stills et al., 1991),
have been isolated from mice and hamsters. The
recently reconstructed family Muridae includes both
mice and hamsters (Alderton, 1996). The Chlamydia
muridarum 16S rRNA genes that have been sequenced
to date differ by 0n13% (using updated SFPD
sequence data), and their 16S­23S intergenic spacers
and 23S domain I segments are identical. Analyses of
other gene sequences can also identify this species.
Glycogen production by both strains has been demonstrated,
although it is difficult to detect in MoPn
(Moulder et al., 1984). MoPn has an extrachromosomal
plasmid, pMoPn. Chlamydia muridarum
MoPn binds mAbs recognizing Chlamydia trachomatis
MOMP vs4 core epitope (T)LNPT(IA) (Peterson et
al., 1991). DNA sequence analysis indicates that these
mAbs should recognize SFPD and that Chlamydia
trachomatis B-serogroup mAbs specific for the vs4
epitope IAGAG should recognize SFPD (Batteiger et
al., 1996). MoPn was isolated in 1942 from the lungs of
asymptomatic albino Swiss mice and was subsequently
shown to be capable of producing disease in mice.
SFPD was obtained from a hamster, concurrent with a
causative agent of proliferative ileitis. MoPn has been
shown to be sensitive to sulfadiazine. The type strain
for Chlamydia muridarum is MoPnT (l ATCC VR
123T).
Description of Chlamydia suis sp. nov.
Chlamydia suis (suhis. L. fem. n. sus pig; L. fem. gen. n.
suis of the pig, because the only currently known
natural host is Sus scrofa).
Chlamydia suis has recently been characterized and has
only been isolated from swine. A high incidence of
Chlamydia suis is being found in enteric porcine
specimens, indicating that it may be endemic (Schiller
et al., 1997; Szeredi et al., 1996; Zahn et al., 1995). The
Chlamydia suis 16S rRNA genes that have been
sequenced to date differ by 1n1%. Glycogen has
been detected in Chlamydia suis inclusions in infected
swine tissues and in cell culture. Some strains have
enhanced resistance to sulfadiazine and tetracycline
(Andersen & Rogers, 1998). Several strains of
Chlamydia suis are known to have an extrachromosomal
plasmid, pCS (Table 4). DNA sequence
analysis of ompA indicates that Chlamydia suis strains
are somewhat more diverse than are other chlamydial
species. The deduced ompA gene products of various
Chlamydia suis strains contain vs4 epitopes TLNPTIAG(A\K\T)G(D\K\N\T),
TWNPTIAGAGS or
TLNPTISGKGQ. These epitopes are identical or
nearly identical to the Chlamydia MOMP core epitopes
NPTI, TLNPTI, LNPTIA or LNPTI, which are
recognized by Chlamydia trachomatis vs4 mAbs; they
are also identical or nearly identical to TIAGAGD
and IAGAG epitopes, which are recognized by
Chlamydia trachomatis B-serogroup mAbs (Batteiger
et al., 1996). Chlamydia suis is associated with conInternational
Journal of Systematic Bacteriology 49 431
K. D. E. Everett, R. M. Bush and A. A. Andersen
junctivitis, enteritis and pneumonia (Rogers &
Andersen, 1996; Rogers et al., 1996). The type strain
for Chlamydia suis is S45T (l ATCC VR 1474T).
Description of the genus Chlamydophila gen. nov.
Chlamydophila (Chla.my.dohphil.a. Gr. fem. n.
chlamys, chlamydis a cloak; L. fem. n. phila dear,
beloved; M.L. fem. n. Chlamydophila dear to the
cloak).
Chlamydophila is one of two genera in the
Chlamydiaceae and is composed of the current species
Chlamydia pecorum, Chlamydia pneumoniae and
Chlamydia psittaci. These taxa, therefore, are renamed
Chlamydophila pecorum, Chlamydophila pneumoniae
and Chlamydophila psittaci. The complete 16S rRNA
and 23S rRNA genes of Chlamydophila species are
95% identical. Chlamydophila species are readily
identified and distinguished from other species by
ribosomal signature sequences (Figs 3 and 4), or by
inspection of the ribosomal intergenic spacer (Everett
& Andersen, 1997). Any of several other genes may
also be used to identify Chlamydophila species on the
basis of DNA homology. The Chlamydophila genome
is approximately 1n2 Mbp. Chlamydophila species do
not produce detectable quantities of glycogen. The
Chlamydophila genome is slightly larger than the
Chlamydia genome and contains a single ribosomal
operon (Fig. 5) (Fukushi & Hirai, 1993; Scieux et al.,
1992). Chlamydophila strains have varying
morphology and varying resistance to sulfadiazine.
Extrachromosomal plasmid is present in many
Chlamydophila species (Table 4). The type species for
the genus Chlamydophila is Chlamydophila psittaci.
Emended description of Chlamydophila pecorum
(Fukushi and Hirai 1992) comb. nov.
The proposal to establish two genera in the family
Chlamydiaceae necessitates transfer of the species
Chlamydia pecorum, which has been described previously
(Fukushi & Hirai, 1992), to the species
Chlamydophila pecorum comb. nov. The emended
Chlamydophila pecorum strains have a high degree of
ribosomal sequence conservation; Chlamydophila
pecorum 16S rRNA genes that have been sequenced to
date differ by 0n6%. Analyses of signature sequences
(Figs 3 and 4) or of several other gene sequences can
help identify this species. Two strains have been shown
to have extrachromosomal plasmids (Table 4).
Chlamydophila pecorum strains are generally noninvasive
in a mouse model of virulence (Rodolakis et
al., 1989; Rodolakis & Souriau, 1992; A. Rodolakis,
personal communication), but are serologically and
pathogenically diverse. Chlamydophila pecorum strains
characterized thus far have been limited to mammals,
but not to a specific host family: Chlamydophila
pecorum has been isolated from ruminants (cattle,
sheep and goats) (Denamur et al., 1991; Fukushi &
Hirai, 1992), a marsupial (koala) (Girjes et al., 1993;
Glassick et al., 1996; M. Jackson et al., 1997) and
swine (Anderson et al., 1996; Everett & Andersen,
1997; Kaltenboeck & Storz, 1992). In koalas,
Chlamydophila pecorum causes reproductive disease,
infertility and urinary tract disease. In other animals,
Chlamydophila pecorum has been associated with
abortion, conjunctivitis, encephalomyelitis, enteritis,
pneumonia and polyarthritis (Anderson et al., 1996;
Kaltenboeck et al., 1993). The type strain for
Chlamydophila pecorum is E58T (l ATCC VR 628T).
Description of Chlamydophila pneumoniae
(Grayston, Kuo, Campbell and Wang 1989) comb.
nov.
The proposal to establish two genera in the family
Chlamydiaceae necessitates transfer of the species
Chlamydia pneumoniae (Grayston et al., 1989) to the
species Chlamydophila pneumoniae comb. nov.
Chlamydophila pneumoniae is considered to be primarily
a respiratory pathogen. The emended species,
Chlamydophila pneumoniae, has been isolated from
humans worldwide (Kuo et al., 1995). In addition, a
number of isolates obtained from koalas and a horse
have genetic and antigenic characteristics very similar
to the human isolates, which warrants including all of
these in Chlamydophila pneumoniae (Glassick et al.,
1996; Storey et al., 1993). DNA sequence analyses of
ompA indicate that the amino acid sequence of MOMP
in all Chlamydophila pneumoniae strains varies 6%,
while other species are 30% different from
Chlamydophila pneumoniae. The coherence of the
Chlamydophila pneumoniae taxon has also been demonstrated
by DNA sequence analysis of rRNA, kdtA
(KDO-transferase), and the 60 kDa cysteine-rich gene.
Partial analysis of any of these genes or analysis of
signature sequences (Figs 3 and 4) can be used to
identify this species. Only the equine strain, N16, has
an extrachromosomal plasmid (pCpnE1). Three
biovars, TWAR, Koala and Equine, are proposed
within Chlamydophila pneumoniae, based on genetic
and biological differences. The type strain for
Chlamydophila pneumoniae is TW-183T (l ATCC VR
2282T).
Chlamydophila pneumoniae, biovar TWAR. Previously,
strain TWAR was synonymous with the designation
of Chlamydia pneumoniae (Kuo et al., 1995). The
description of biovar TWAR is identical to the
description of the prototypical TWAR serovar
(Grayston et al., 1989), except that biovar TWAR EBs
may have either of two distinct ultrastructural
morphologies: the prototypical pear-shaped EB
(Grayston et al., 1989) or the classic coccoid morphology
of the Chlamydiaceae spp. (Carter et al., 1991;
Miyashita et al., 1993; Popov et al., 1991). The name
TWAR was formed by merging the first two letters of
isolates TW-183 and AR-39 (Grayston et al., 1989).
TWAR strains have been obtained only from humans,
form a distinct serovar, and are genetically almost
indistinguishable (Kuo et al., 1995; Pettersson et al.,
432 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
1997). TWAR is primarily a pathogen of the respiratory
tract, predominantly causing acute or chronic
bronchitis and pneumonia. TWAR has also been
associated with acute and chronic respiratory diseases
such as otitis media, obstructive pulmonary disease
and pulmonary exacerbation of cystic fibrosis. It has
also been associated with Alzheimer's, atherosclerosis,
asthma, erythema nodosum, reactive airway disease,
Reiter's syndrome and sarcoidosis (Balin et al., 1998;
Braun et al., 1997; Ellis, 1997; L. A. Jackson et al.,
1997; Kuo et al., 1995). The reference strain for the
TWAR biovar is TW-183T.
Chlamydophila pneumoniae, biovar Koala. Chlamydophila
pneumoniae isolates obtained from the marsupial
Phascolarctos cinereus have distinctive features that
merit separation of the Koala biovar from the TWAR
biovar. All isolates to date have only been obtained
from Phascolarctos cinereus. The MOMP in the Koala
biovar isolate designated `Type I' is 2n2% different
from the protein homologue in TWAR, 5n5% different
from Equine MOMP, and 30% different from
MOMP in other chlamydial species. The KDOtransferase
of Koala biovar Type I and TWAR differ
by 8% (Girjes et al., 1997), but are 40% different
from the kdtA product in other chlamydial species.
The TWAR mAb, CeLLabs-28E, does not recognize
the Type I isolate (Girjes et al., 1994). Ultrastructural
analyses of Type I EBs show the classic coccoid
morphology of the Chlamydiaceae spp. (Girjes et al.,
1993). The Koala biovar of Chlamydophila pneumoniae
is further differentiated from other biovars of Chlamydophila
pneumoniae by the sequence of variable
segment 4 of ompA (Wardrop et al., 1999; eight
isolates), the partial 60 kDa cysteine-rich gene (Glassick
et al., 1996; two isolates), and the groESL
intergenic region (Wardrop et al., 1999). Chlamydiae
belonging to the Koala biovar of Chlamydophila
pneumoniae have been identified in all five Australian
free-ranging koala populations that have been tested,
including a colony that was suffering from respiratory
disease. Isolates are commonly obtained from ocular
and urogenital sites, where they do not appear to be
highly pathogenic. The reference strain for the Koala
biovar is LPCon.
Chlamydophila pneumoniae, biovar Equine. The Equine
biovar of Chlamydophila pneumoniae currently includes
only strain N16, which was isolated from the
respiratory tract of a horse (Wills et al., 1990). The
MOMP of N16 is 5n5% different from that in other
Chlamydophila pneumoniae isolates (Storey et al., 1993)
and 30% different from other chlamydial species.
The 16S rRNA of Chlamydophila pneumoniae strain
N16 differs 1n1% from TWAR 16S rRNA and 4%
from the 16S rRNA of other chlamydial species. N16
and TWAR 16S­23S intergenic spacer differ by 0n9%,
and they are 11n3% different from other chlamydial
species. The 23S rRNA Domain I of N16 and TWAR
differ by 1n3%, and are 5n6% different from other
chlamydial species. Two mAbs have been identified
that are specific for the TWAR biovar, but that do not
recognize N16 (Storey et al., 1993). Ultrastructural
analyses of N16 EBs show the classic coccoid morphology
of the Chlamydiaceae spp. (Wills et al., 1990).
Inoculation of horses with N16 leads to asymptomatic
infections (Mair & Wills, 1992). The reference strain
for the Equine biovar is N16.
Description of Chlamydophila psittaci (Page 1968)
comb. nov.
Chlamydia psittaci, as previously described (Moulder
et al., 1984), has been a taxon with considerable
heterogeneity, having four groups that are phenotypically,
pathogenically and genetically distinct. Only
avian-like strains are being retained in Chlamydophila
psittaci, with specific former Chlamydia psittaci
abortion, feline and guinea pig strains being transferred
into three new species. According to Rule 40b of
the International Code of Nomenclature of Bacteria,
the original epithet for Chlamydia psittaci is retained
by Chlamydophila psittaci because it contains avian
strain 6BCT, the original type strain (Lapage et al.,
1992). As emended, Chlamydophila psittaci 16S rRNA
genes differ by 0n8%. Analyses of other gene
sequences can also help identify this species. Isolates
are similar in virulence and grow readily in cell culture.
All should be considered to be readily transmissible to
humans. Several Chlamydophila psittaci strains have
an extrachromosomal plasmid (Table 4). Many
Chlamydophila psittaci strains are susceptible to bacteriophage
Chp1 (Storey et al., 1992). The type strain
for Chlamydophila psittaci is 6BCT (l ATCC VR
125T).
The emended species, Chlamydophila psittaci, has eight
known serovars that are readily distinguished using
serovar-specific mAbs (Andersen, 1991, 1997;
Vanrompay et al., 1993). These specific serovars can
also be identified by ompA sequence differences. Some
serovars have a capability for infecting more than one
type of host (Andersen et al., 1997; Centers for Disease
Control and Prevention, 1997; Francis & Magill, 1938;
Page, 1967; Spalatin et al., 1966; Vanrompay et al.,
1994). Serovar A is endemic among psittacine birds
and causes sporadic zoonotic disease in humans.
Serovar A infection of birds is often systemic and can
be inapparent, severe, acute or chronic with intermittent
shedding. Serovar B is endemic among
pigeons, has been isolated from turkeys, and has also
been identified as the cause of abortion in a dairy herd.
Serovar C isolates GD, CT1 and Par1 were obtained
from duck, turkey and partridge, respectively, so a
specific avian host family has not been identified.
Serovar D strains have been isolated from turkeys, a
seagull, a budgerigar and humans. Serovars C and D
are occupational hazards for slaughterhouse workers
and for people in contact with birds. Serovar E isolates,
known as Cal-10, MP or MN (meningopneumonitis),
were first isolated during an outbreak of pneumonitis
in humans in the late 1920s and early 1930s. Subsequently,
MN isolates have been obtained from a
International Journal of Systematic Bacteriology 49 433
K. D. E. Everett, R. M. Bush and A. A. Andersen
variety of avian hosts worldwide, including ducks,
pigeons, ostriches and rheas (Andersen et al., 1998).
These isolations often come from ill or dying birds,
and a specific reservoir for serovar E has not been
identified. A single serovar F isolate, VS225, was
obtained from a parakeet. The M56 serovar was
isolated during an outbreak in muskrats and hares.
The WC serovar was isolated during an outbreak of
enteritis in cattle. Other monoclonal serotyping
systems have also been developed (Fukushi et al.,
1987; Takahashi et al., 1988, 1997), but a comparative
study of these methods has not been done.
Description of Chlamydophila abortus sp. nov.,
including abortion isolates previously belonging to
Chlamydia psittaci
Chlamydophila abortus (a.borhtus. L. masc. gen. n.
abortus of miscarriage, referring to the principal
symptom of infection).
Chlamydophila abortus strains are endemic among
ruminants and efficiently colonize the placenta
(Rodolakis et al., 1989). They have a distinctive
serotype and nearly 100% conservation of ribosomal
and ompA sequences. The Chlamydophila abortus 16S
rRNA genes that have been sequenced to date differ by
0n07%. Analyses of signature sequences (Figs 3 and
4) or other gene sequences readily identify this species.
An extrachromosomal plasmid has not been identified
in any strain of Chlamydophila abortus. Chlamydophila
abortus has been primarily associated with cases of
abortion and weak neonates. Typical isolates include
strains B577, EBA, OSP, S26\3 and A22 and have
been obtained from cases of abortion in sheep, cattle
and goats worldwide (Andersen, 1991; Denamur et al.,
1991; Storz et al., 1960). Chlamydophila abortus
isolates have also been characterized by serology and
sequence analysis from cases of abortion in a horse, a
rabbit, guinea pigs and mice (J. Storz, K. D. E. Everett,
A. A. Andersen, unpublished data) and by PCR from
a pig (Kaltenbo$ ck et al., 1997). Sporadic zoonotic
abortion due to Chlamydophila abortus has been
confirmed by genetic analysis of isolates from women
who work with sheep (Herring et al., 1987; Jorgensen,
1997). The type strain for Chlamydophila abortus is
B577T (l ATCC VR 656T). B577T has a slightly
divergent rDNA sequence compared to other
Chlamydophila abortus strains.
Description of Chlamydophila felis sp. nov., including
feline isolates previously belonging to Chlamydia
psittaci
Chlamydophila felis (fehlis. L. gen. n. felis of the cat,
because the domestic cat is the primary host of the
strains identified to date).
Chlamydophila felis is endemic among house cats
worldwide, primarily causing conjunctivitis and rhinitis
(Gaillard et al., 1984; TerWee et al., 1998).
Chlamydophila felis strains are characterized by a high
degree of rRNA and ompA conservation and have a
distinctive serotype (Andersen, 1991; Pudjiatmoko et
al., 1997; Sayada et al., 1994). The Chlamydophila felis
16S rRNA genes that have been sequenced to date
differ by 0n6%. Strains FP Pring and FP Cello have
an extrachromosomal plasmid, while the FP Baker
strain does not. FP Cello produces lethal disease in
mice while the FP Baker does not (May et al., 1996).
An attenuated FP Baker strain is used as a live vaccine
for cats. Zoonotic infection of humans with
Chlamydophila felis has been reported (Schachter et
al., 1969). The type strain for Chlamydophila felis is FP
BakerT (l ATCC VR 120T).
Description of Chlamydophila caviae sp. nov.,
including guinea pig inclusion conjunctivitis isolates
previously belonging to Chlamydia psittaci
Chlamydophila caviae [cahvi.ae. L. gen. fem. n. caviae
of the guinea pig (Cavia cobaya) because the type
strain was isolated from Cavia cobaya].
Chlamydophila caviae was first recovered from the
conjunctiva of guinea pigs and the description of this
species is identical to that of the isolate GPIC (Gordon
et al., 1966; Murray, 1964; Prain & Pearce, 1989).
There are five known Chlamydophila caviae isolates,
and the ompA (omp1) sequences of these isolates are
identical (Zhao et al., 1993). Analyses of signature
sequences (Figs 3 and 4) or other gene sequences,
including 16S rRNA, can be used to distinguish this
species. GPIC contains an extrachromosomal plasmid,
pCpGP1 (Lusher et al., 1989). The natural site of
Chlamydophila caviae infection is the conjunctiva,
however, it is possible to infect the genital tract of
guinea pigs with Chlamydophila caviae and elicit a
disease that is very similar to human genital infection.
Chlamydophila caviae is markedly specific for guinea
pigs, as attempts to infect mice, hamsters, rabbits and
gerbils have been unsuccessful, except for one experimentally
infected gerbil. Chlamydophila caviae
infects primarily the mucosal epithelium and is not
invasive. The type strain for Chlamydophila caviae is
GPICT (l ATCC VR 813T).
Description of Parachlamydiaceae fam. nov.
Parachlamydiaceae (Par.a.chla.my.di.ahce.ae. M.L.
fem. n. Parachlamydia type genus of the family; -aceae
ending to denote a family; M.L. fem. pl. n. Parachlamydiaceae
the Parachlamydia family).
The Parachlamydiaceae naturally infect amoebae
and can be grown in cultured Vero cells. The
Parachlamydiaceae are not recognized by monoclonal
antibodies specific for the antigenic LPS trisaccharide
Kdo-(2 8)-Kdo-(2 4)-Kdo of the
Chlamydiaceae. The description of this family derives
from the description of `Candidatus Parachlamydia
acanthamoebae' strain Bn
*
T, strain Berg
"(
and several
unnamed isolates (Amann et al., 1997; Birtles et al.,
1997; Michel et al., 1994). The Parachlamydiaceae
434 International Journal of Systematic Bacteriology 49
Reclassification of order Chlamydiales
comprise strains with rRNAs that are 90% identical
to the ribosomal genes of strain Bn
*
T. The
Parachlamydiaceae belong to the order Chlamydiales
and form a sister taxon to the Chlamydiaceae because
they have a chlamydia-like cycle of replication and
their ribosomal genes are 80­90% identical to ribosomal
genes in the Chlamydiaceae. Phylogenetic
analysis of a 16S rRNA from the Parachlamydiaceae
gene has been published previously (Amann et al.,
1997; Pettersson et al., 1997). At present, this
family comprises but a single genus, the type genus
Parachlamydia.
Description of Parachlamydia (Amann, Springer,
Scho$ nhuber, Ludwig, Schmid, Mu$ ller and Michel
1997) gen. nov. `Candidatus Parachlamydia' Amann,
Springer, Scho$ nhuber, Ludwig, Schmid, Mu$ ller and
Michel 1997
Parachlamydia (Par.a.chla.myhdi.a. Gr. prep. para
alike, alongside of; M.L. fem. n. Chlamydia taxonomic
name of a bacterial genus).
Currently the description of Parachlamydia corresponds
to the description of the family Parachlamydiaceae.
Parachlamydia have variable Gram
staining characteristics and are mesophilic. The 16S
and\or 23S rRNA genes of known members of
Parachlamydia are 95% identical to those of the
type species, Parachlamydia acanthamoebae. New
members of this genus should have 95% rRNA
sequence identity with Parachlamydia acanthamoebae.
Description of Parachlamydia acanthamoebae sp.
nov. `Candidatus Parachlamydia acanthamoebae'
Amann, Springer, Scho$ nhuber, Ludwig, Schmid,
Mu$ ller and Michel 1997
Parachlamydia acanthamoebae [acan.tha.moehbae.
M.L. gen. sing. n. of Acanthamoeba taxonomic name
of a genus of Acanthamoebidae; of (living in) members
of the genus Acanthamoeba].
Parachlamydia acanthamoebae sp. nov. currently
includes the type strain Bn
*
T (l ATCC VR 1476T),
isolate Berg
"(
and several unnamed isolates (Amann et
al., 1997; Birtles et al., 1997; Michel et al., 1994). The
16S rRNA and rDNA of Parachlamydia acanthamoebae
can be specifically detected with oligonucleotide
probe Bn
*
658: 5h TCCGTTTTCTCCGCCTAC
3h. Trophozoites of Acanthamoeba hosting
these strains were isolated from humans in an outbreak
of humidifier fever in Vermont USA (`Hall's coccus')
and also from asymptomatic women in Germany. In
Nova Scotia, four patients whose sera recognized
Hall's coccus did not show serological cross-reaction
with antigens from the Chlamydiaceae (Birtles et al.,
1997).
Description of Simkaniaceae fam. nov.
Simkaniaceae (Sim.ka.ni.ahce.ae. M.L. fem. n.
Simkania type genus of the family; -aceae ending to
denote a family; M.L. fem. pl. n. Simkaniaceae the
Simkania family).
The family Simkaniaceae currently comprises but a
single genus, the type genus Simkania. The description
of this family corresponds to that of the `microorganism
Z' (Kahane et al., 1993, 1995, 1999). The
Simkaniaceae are not recognized by mAbs specific for
the antigenic LPS trisaccharide Kdo-(2 8)-Kdo(2
4)-Kdo of the Chlamydiaceae. Simkaniaceae
belongs to the order Chlamydiales and is a sister taxon
of the Chlamydiaceae because it has a chlamydia-like
cycle of replication and the ribosomal genes are
80­90% identical to ribosomal genes in the
Chlamydiaceae. Phylogenetic analyses of the
Simkaniaceae 16S rRNA gene have been published
previously (Amann et al., 1997; Kahane et al., 1995;
Pettersson et al., 1997). New strains belonging to the
Simkaniaceae should have ribosomal genes that are
90% identical to the ribosomal genes of strain ZT.
The type genus for Simkaniaceae is Simkania.
Description of Simkania gen. nov.
Simkania (Sim.kahni.a. M.L. fem. n. Simkania arbitrary
name formed from the personal name Simona
Kahane).
Currently the description of Simkania corresponds to
the description of the family Simkaniaceae and
includes a single isolate, strain ZT. The natural host of
Simkania is not known, but serological evidence and
PCR indicate that it is widespread among humans.
New members of the genus Simkania should have 16S
or 23S rRNA genes that are 95% identical to those
of Simkania negevensis, the type species.
Description of Simkania negevensis sp. nov.
Simkania negevensis (ne.ge.venhsis. M.L. adj.
negevensis of or pertaining to the Negev, a desert in
southern Israel).
The species Simkania negevensis currently includes
only the type strain, Simkania negevensis strain ZT (l
ATCC VR 1471T). Simkania negevensis was discovered
as a bacterial contaminant in cell cultures. The
description of this species is derived from that of the
`micro-organism Z' (Kahane et al., 1993, 1995, 1999).
Strain ZT does not contain an extrachromosomal
plasmid and has an unusually slow developmental
cycle in cultured Vero cells (up to 14 d), compared to
other chlamydiae. Unlike other chlamydial rRNA
genes that have been characterized, Simkania
negevensis has a group I intron in 23S rRNA position
1931 (E. coli numbering) and this intron is not spliced
out of the rRNA. The intron is closely related to group
I introns in the 23S rRNA of chloroplasts and
mitochondria in algae and amoebae.
International Journal of Systematic Bacteriology 49 435
K. D. E. Everett, R. M. Bush and A. A. Andersen
Rapid identification and classification of new
chlamydial strains
Identification of strains can be readily and accurately
performed to determine whether a specimen belongs to
one of the nine groups in the Chlamydiaceae, to
Simkaniaceae, to Parachlamydiaceae, or is similar to
strain WSU 86-1044. Three simple PCR methods have
been described (Everett et al., 1999). Another simple
method is to PCR-amplify and directly sequence the
16S and\or 23S signature sequences from chromosomal
template and to compare these data with Figs 3
or 4. When GenBank entries have been updated to
reflect the new groups, identification of signature
sequences will also be possible by using a BLAST search
of that database. Because it is essential to have good
sequence data to make these determinations, template
preparations for PCR may need to be free of contamination
with other bacterial templates or, alternatively,
sequence data can be obtained from cloned gene
segments. If other bacteria are present in the
chlamydial isolate, hot-start PCR methods may partially
alleviate the frequency of mismatch amplification
of contaminating template. If cloning is necessary, a
conserved PbrP1 restriction site has been identified in
the 23S sequence to facilitate the selection of 23S
signature sequence clones (Fig. 4b). Sequence data not
matching a species in Fig. 3 or 4 will represent either a
novel isolate or a non-chlamydial organism. Novel
isolates require more extensive phenotypic characterization
and\or sequence analysis before they can be
validly identified.
DNA sequence analysis of the ribosomal intergenic
spacer or of non-ribosomal genes can be used to
corroborate signature sequence identification of the
Chlamydiaceae. Members of strains belonging to the
family Chlamydiaceae are also identified using mAbs
that recognize the trisaccharide antigen Kdo-(2 8)Kdo-(2
4)-Kdo, a unique component of the LPS
and previously referred to as a genus-specific marker
(Lo$ bau et al., 1995).
ACKNOWLEDGEMENTS
The authors wish to thank Linda Hornung for the isolation
of swine strains and for the propagation of other strains used
in this work. We thank Wendy Hambly for technical
assistance with ompA analysis. We thank Gary Polking,
Harold `Hal' Hills and Tim Ingram for providing outstanding
data acquisition facilities. We thank Shirley M.
Halling for making available sequence analysis software,
computer time and radiolabelling facilities, and Richard L.
Zuerner for providing PFGE equipment and assistance. We
thank Pam Dilbeck and Fred Rurangirwa for making
prepublication data available. We are gratefully indebted to
Byron Batteiger, Bernhard Kaltenboeck, James W.
Moulder, Roger G. Rank, Thaddeus Stanton, Johannes
Storz, Peter Timms and Michael E. Ward for providing
information and for their critical reviews of the preliminary
drafts of this report. We also thank others who have
contributed information in the compilation and review of
these data and Karl Dyszynski for assistance in preparation
of the manuscript. We thank Hans G. Tru$ per and Johannes
Storz for assisting with the naming of new taxa. We are
honoured to comply with the requests of Rudolf Amann,
Simona Kahane and Maureen G. Friedman that we formally
classify their isolates in this proposal.
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