Chlamydiota

Among the Chlamydiota, all of the ones long known to science grow only by infecting eukaryotic host cells. They are as small as or smaller than many viruses. They are ovoid in shape and stain Gram-negative. They are dependent on replication inside the host cells; thus, some species are termed obligate intracellular pathogens and others are symbionts of ubiquitous protozoa. Most intracellular Chlamydiota are located in an inclusion body or vacuole; when growing in a cell, they survive in a metabolically active but noninfectious form called the reticulate body. Outside cells, they survive only as an infectious, spore-like form called the elementary body.

These Chlamydiota can grow only where their host cells grow, and develop according to a characteristic biphasic developmental cycle.{{cite journal | vauthors = Horn M | title = Chlamydiae as symbionts in eukaryotes | journal = Annual Review of Microbiology | volume = 62 | pages = 113–131 | year = 2008 | pmid = 18473699 | doi = 10.1146/annurev.micro.62.081307.162818 | s2cid = 13405815 }}{{cite journal | vauthors = Abdelrahman YM, Belland RJ | title = The chlamydial developmental cycle | journal = FEMS Microbiology Reviews | volume = 29 | issue = 5 | pages = 949–959 | date = November 2005 | pmid = 16043254 | doi = 10.1016/j.femsre.2005.03.002 | doi-access = free }}{{cite journal | vauthors = Horn M, Collingro A, Schmitz-Esser S, Beier CL, Purkhold U, Fartmann B, Brandt P, Nyakatura GJ, Droege M, Frishman D, Rattei T, Mewes HW, Wagner M | display-authors = 6 | title = Illuminating the evolutionary history of Chlamydiae | journal = Science | volume = 304 | issue = 5671 | pages = 728–730 | date = April 2004 | pmid = 15073324 | doi = 10.1126/science.1096330 | s2cid = 39036549 | bibcode = 2004Sci...304..728H | doi-access = free }} Therefore, clinically relevant Chlamydiota cannot be propagated in bacterial culture media in the clinical laboratory. They are most successfully isolated while still inside their host cells.

In 2020 many additional Chlamydiota were discovered in ocean-floor environments, and it is not yet known whether they all have hosts.

Scientists have long known that Chlamydiota are susceptible to antibiotics that target the production of peptidoglycan (PG) such as penicillin, yet have for a long time failed to find any PG in their cell walls.{{cite journal | vauthors = Jacquier N, Viollier PH, Greub G | title = The role of peptidoglycan in chlamydial cell division: towards resolving the chlamydial anomaly | journal = FEMS Microbiology Reviews | volume = 39 | issue = 2 | pages = 262–275 | date = March 2015 | pmid = 25670734 | doi = 10.1093/femsre/fuv001 | doi-access = free }} In 2013, Protochlamydia amoebophila was shown to have a sacculus made of PG while Simkania negevensis does not. There is no FtsZ gene, which is previously believed to be essential for cell division in the presence of PG, in either of them.{{cite journal | vauthors = Pilhofer M, Aistleitner K, Biboy J, Gray J, Kuru E, Hall E, Brun YV, VanNieuwenhze MS, Vollmer W, Horn M, Jensen GJ | display-authors = 6 | title = Discovery of chlamydial peptidoglycan reveals bacteria with murein sacculi but without FtsZ | journal = Nature Communications | volume = 4 | issue = 1 | pages = 2856 | date = 2013-12-02 | pmid = 24292151 | doi = 10.1038/ncomms3856 | pmc = 3847603 | bibcode = 2013NatCo...4.2856P }} In 2014, the human pathogen Chlamydia trachomatis was shown to contain PG in its intracellular stage, apparently forming rings.{{cite journal | vauthors = Liechti GW, Kuru E, Hall E, Kalinda A, Brun YV, VanNieuwenhze M, Maurelli AT | title = A new metabolic cell-wall labelling method reveals peptidoglycan in Chlamydia trachomatis | journal = Nature | volume = 506 | issue = 7489 | pages = 507–510 | date = February 2014 | pmid = 24336210 | doi = 10.1038/nature12892 | pmc = 3997218 | bibcode = 2014Natur.506..507L }} In 2016, the role of PG in Chlamydia was clarified using more data: it does not make a whole sacculus around the cell like usual bacteria and Protochlamydia do, but instead produces a thin ring of PG down the middle during cell division. MreB controls the production of the ring, taking up the role that FtsZ would've performed. This explains why penicillin is bacteriostatic and not bacteriocidal to Chlamydia.{{cite journal | vauthors = Liechti G, Kuru E, Packiam M, Hsu YP, Tekkam S, Hall E, Rittichier JT, VanNieuwenhze M, Brun YV, Maurelli AT | display-authors = 6 | title = Pathogenic Chlamydia Lack a Classical Sacculus but Synthesize a Narrow, Mid-cell Peptidoglycan Ring, Regulated by MreB, for Cell Division | journal = PLOS Pathogens | volume = 12 | issue = 5 | pages = e1005590 | date = May 2016 | pmid = 27144308 | pmc = 4856321 | doi = 10.1371/journal.ppat.1005590 | doi-access = free }}

The elemental bodies of Chlamydia is characterized by the presence of a tough cell wall. This wall is not made of PG, but instead consists of a network of proteins.{{cite journal |last1=Elwell |first1=Cherilyn |last2=Mirrashidi |first2=Kathleen |last3=Engel |first3=Joanne |title=Chlamydia cell biology and pathogenesis |journal=Nature Reviews. Microbiology |date=June 2016 |volume=14 |issue=6 |pages=385–400 |doi=10.1038/nrmicro.2016.30|pmid=27108705 |pmc=4886739 }}

Chlamydia-like disease affecting the eyes of people was first described in ancient Chinese and Egyptian manuscripts. A modern description of chlamydia-like organisms was provided by Halberstaedrrter and von Prowazek in 1907.

Chlamydial isolates cultured in the yolk sacs of embryonating eggs were obtained from a human pneumonitis outbreak in the late 1920s and early 1930s, and by the mid-20th century, isolates had been obtained from dozens of vertebrate species. The term chlamydia (a cloak) appeared in the literature in 1945, although other names continued to be used, including Bedsonia, Miyagawanella, ornithosis-, TRIC-, and PLT-agents. In 1956, Chlamydia trachomatis was first cultured by Tang Fei-fan, though they were not yet recognized as bacteria.{{cite book |author = Philip S. Brachman and Elias Abrutyn |title = Bacterial Infections of Humans: Epidemiology and Control |date = 2009-07-23 |publisher = Springer |isbn = 9780387098425}}

In 1966, Chlamydiota were recognized as bacteria and the genus Chlamydia was validated.{{cite journal | vauthors = Moulder JW | title = The relation of the psittacosis group (Chlamydiae) to bacteria and viruses | journal = Annual Review of Microbiology | volume = 20 | pages = 107–130 | year = 1966 | pmid = 5330228 | doi = 10.1146/annurev.mi.20.100166.000543 }} The order Chlamydiales was created by Storz and Page in 1971. The class Chlamydiia was recently validly published.{{cite journal | vauthors = Gupta RS, Naushad S, Chokshi C, Griffiths E, Adeolu M | title = A phylogenomic and molecular markers based analysis of the phylum Chlamydiae: Proposal to divide the class Chlamydiia into two orders, Chlamydiales and Parachlamydiales ord. nov., and emended description of the class Chlamydiia | journal = Antonie van Leeuwenhoek | volume = 108 | issue = 3 | pages = 765–781 | date = September 2015 | pmid = 26179278 | doi = 10.1007/s10482-015-0532-1 | s2cid = 17099157 }}{{cite journal | vauthors = Oren A, Garrity GM | title = List of new names and new combinations previously effectively, but not validly, published | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 66 | issue = 7 | pages = 2463–2466 | date = July 2016 | pmid = 27530111 | doi = 10.1099/ijsem.0.001149 | doi-access = free }}{{cite journal | doi = 10.1099/00207713-21-4-332 |vauthors=Storz J, Page LA | title = Taxonomy of the Chlamydiae: reasons for classifying organisms of the genus Chlamydia, family Chlamydiaceae, in a separate order, Chlamydiales ord. nov | journal = International Journal of Systematic Bacteriology | year = 1971 | volume = 21 | pages = 332–334 | issue = 4 | doi-access = free }} Between 1989 and 1999, new families, genera, and species were recognized. The phylum Chlamydiae was established in Bergey's Manual of Systematic Bacteriology.{{cite book | vauthors = Garrity GM, Boone DR | title = Bergey's Manual of Systematic Bacteriology Volume 1: The Archaea and the Deeply Branching and Phototrophic Bacteria | edition = 2nd | publisher = Springer | year = 2001 | isbn = 978-0-387-98771-2 | url-access = registration | url = https://archive.org/details/bergeysmanualofs00boon }} By 2006, genetic data for over 350 chlamydial lineages had been reported.{{cite journal | vauthors = Everett KD, Thao M, Horn M, Dyszynski GE, Baumann P | title = Novel chlamydiae in whiteflies and scale insects: endosymbionts 'Candidatus Fritschea bemisiae' strain Falk and 'Candidatus Fritschea eriococci' strain Elm | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 55 | issue = Pt 4 | pages = 1581–1587 | date = July 2005 | pmid = 16014485 | doi = 10.1099/ijs.0.63454-0 | doi-access = free }} Discovery of ocean-floor forms reported in 2020 involves new clades. In 2022 the phylum was renamed Chlamydiota.

The Chlamydiota currently contain eight validly named genera, and 14 genera.{{cite web |author = Sayers| url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Tree&id=204429&lvl=3&p=mapview&p=has_linkout&p=blast_url&p=genome_blast&lin=f&keep=1&srchmode=1&unlock|title=Chlamydiia |access-date=2016-10-24 |publisher=National Center for Biotechnology Information (NCBI) taxonomy database |display-authors=etal}} The phylum presently consist of two orders (Chlamydiales, Parachlamydiales) and nine families within a single class (Chlamydiia). Only four of these families are validly named (Chlamydiaceae, Parachlamydiaceae, Simkaniaceae, Waddliaceae){{cite journal | vauthors = Everett KD, Bush RM, Andersen AA | title = 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 | journal = International Journal of Systematic Bacteriology | volume = 49 | issue = Pt 2 | pages = 415–440 | date = April 1999 | pmid = 10319462 | doi = 10.1099/00207713-49-2-415 | doi-access = free }}{{cite journal | vauthors = Rurangirwa FR, Dilbeck PM, Crawford TB, McGuire TC, McElwain TF | title = Analysis of the 16S rRNA gene of micro-organism WSU 86-1044 from an aborted bovine foetus reveals that it is a member of the order Chlamydiales: proposal of Waddliaceae fam. nov., Waddlia chondrophila gen. nov., sp. nov | journal = International Journal of Systematic Bacteriology | volume = 49 | issue = Pt 2 | pages = 577–581 | date = April 1999 | pmid = 10319478 | doi = 10.1099/00207713-49-2-577 | doi-access = free }} while five are described as families (Clavichlamydiaceae, Criblamydiaceae, Parilichlamydiaceae, Piscichlamydiaceae, and Rhabdochlamydiaceae).{{cite journal | vauthors = Thomas V, Casson N, Greub G | title = Criblamydia sequanensis, a new intracellular Chlamydiales isolated from Seine river water using amoebal co-culture | journal = Environmental Microbiology | volume = 8 | issue = 12 | pages = 2125–2135 | date = December 2006 | pmid = 17107554 | doi = 10.1111/j.1462-2920.2006.01094.x | bibcode = 2006EnvMi...8.2125T | s2cid = 31211875 }}{{cite journal | vauthors = Stride MC, Polkinghorne A, Miller TL, Groff JM, Lapatra SE, Nowak BF | title = Molecular characterization of "Candidatus Parilichlamydia carangidicola," a novel Chlamydia-like epitheliocystis agent in yellowtail kingfish, Seriola lalandi (Valenciennes), and the proposal of a new family, "Candidatus Parilichlamydiaceae" fam. nov. (order Chlamydiales) | journal = Applied and Environmental Microbiology | volume = 79 | issue = 5 | pages = 1590–1597 | date = March 2013 | pmid = 23275507 | pmc = 3591964 | doi = 10.1128/AEM.02899-12 | bibcode = 2013ApEnM..79.1590S }}Kuo C-C, Horn M, Stephens RS (2011) Order I. Chlamydiales. In: Bergey's Manual of Systematic Bacteriology, vol. 4, 2nd ed. pp. 844-845. Eds Krieg N, Staley J, Brown D, Hedlund B, Paster B, Ward N, Ludwig W, Whitman W. Springer-: New York.

The Chlamydiales order as recently described contains the families Chlamydiaceae, and the Clavichlamydiaceae, while the new Parachlamydiales order harbors the remaining seven families. This proposal is supported by the observation of two distinct phylogenetic clades that warrant taxonomic ranks above the family level. Molecular signatures in the form of conserved indels (CSIs) and proteins (CSPs) have been found to be uniquely shared by each separate order, providing a means of distinguishing each clade from the other and supporting the view of shared ancestry of the families within each order.{{cite journal | vauthors = Griffiths E, Ventresca MS, Gupta RS | title = BLAST screening of chlamydial genomes to identify signature proteins that are unique for the Chlamydiales, Chlamydiaceae, Chlamydophila and Chlamydia groups of species | journal = BMC Genomics | volume = 7 | pages = 14 | date = January 2006 | pmid = 16436211 | pmc = 1403754 | doi = 10.1186/1471-2164-7-14 | doi-access = free }} The distinctness of the two orders is also supported by the fact that no CSIs were found among any other combination of families.

Molecular signatures have also been found that are exclusive for the family Chlamydiaceae. The Chlamydiaceae originally consisted of one genus, Chlamydia, but in 1999 was split into two genera, Chlamydophila and Chlamydia. The genera have since 2015 been reunited where species belonging to the genus Chlamydophila have been reclassified as Chlamydia species.{{cite journal | vauthors = Sachse K, Bavoil PM, Kaltenboeck B, Stephens RS, Kuo CC, Rosselló-Móra R, Horn M | title = Emendation of the family Chlamydiaceae: proposal of a single genus, Chlamydia, to include all currently recognized species | journal = Systematic and Applied Microbiology | volume = 38 | issue = 2 | pages = 99–103 | date = March 2015 | pmid = 25618261 | doi = 10.1016/j.syapm.2014.12.004 | bibcode = 2015SyApM..38...99S | hdl = 10261/123714 }}{{cite journal |vauthors=Oren A, Garrity GM |title= List of new names and new combinations previously effectively, but not validly, published |journal=Int J Syst Evol Microbiol |volume=65 |issue= 7 |pages=2017–2025 |year=2015 |doi=10.1099/ijs.0.000317|pmid= 28056215 |pmc= }}

However, CSIs and CSPs have been found specifically for Chlamydophila species, supporting their distinctness from Chlamydia, perhaps warranting additional consideration of two separate groupings within the family. CSIs and CSPs have also been found that are exclusively shared by all Chlamydia that are further indicative of a lineage independent from Chlamydophila, supporting a means to distinguish Chlamydia species from neighbouring Chlamydophila members.

The Chlamydiota form a unique bacterial evolutionary group that separated from other bacteria about a billion years ago, and can be distinguished by the presence of several CSIs and CSPs.{{cite journal | vauthors = Greub G, Raoult D | title = History of the ADP/ATP-translocase-encoding gene, a parasitism gene transferred from a Chlamydiales ancestor to plants 1 billion years ago | journal = Applied and Environmental Microbiology | volume = 69 | issue = 9 | pages = 5530–5535 | date = September 2003 | pmid = 12957942 | pmc = 194985 | doi = 10.1128/AEM.69.9.5530-5535.2003 | bibcode = 2003ApEnM..69.5530G }} The species from this group can be distinguished from all other bacteria by the presence of conserved indels in a number of proteins and by large numbers of signature proteins that are uniquely present in different Chlamydiae species.{{cite journal | vauthors = Griffiths E, Petrich AK, Gupta RS | title = Conserved indels in essential proteins that are distinctive characteristics of Chlamydiales and provide novel means for their identification | journal = Microbiology | volume = 151 | issue = Pt 8 | pages = 2647–2657 | date = August 2005 | pmid = 16079343 | doi = 10.1099/mic.0.28057-0 | doi-access = free }}{{cite journal | vauthors = Gupta RS, Griffiths E | title = Chlamydiae-specific proteins and indels: novel tools for studies | journal = Trends in Microbiology | volume = 14 | issue = 12 | pages = 527–535 | date = December 2006 | pmid = 17049238 | doi = 10.1016/j.tim.2006.10.002 }}

The Chlamydiota is interesting in that the order Chlamydiales (which contains all validly-published members before 2010) have no known free-living members. Considering most bacteria are free-living, there has to be some point when the lineage branched off into being intracellular. Identifying where that branch had happened and the original host remains somewhat controversial.{{cite web|date=2002 |last1=Moulder|first1=James W.|author1-link=James W. Moulder |title=Chlamydial and Chlamydiales evolution - index. |url=http://chlamydiae.com/Evolution_index.asp |archive-url=https://web.archive.org/web/20101120231723/http://chlamydiae.com/Evolution_index.asp |archive-date=20 November 2010 }}

As of 2003 it was commonly believed that Chlamydiota shares a common ancestor with cyanobacteria, the group containing the endosymbiont ancestor to the chloroplasts of modern plants.{{cite web |last1=Moulder|first1=James W.|author1-link=James W. Moulder|date=2008|title=Plant Chlamydia relationships - Chlamydiales evolution - Chlamydia Plant relationships |url=http://chlamydiae.com/docs/Chlamydiales/ev_plants.asp |archive-url=https://web.archive.org/web/20101121000120/http://chlamydiae.com/docs/Chlamydiales/ev_plants.asp |archive-date=21 November 2010 }} This was due to studies showing specific genes, later entire genomic contents, to be most similar to cyanobacteria and land plants. A 2004 study found that 11% of the genes in Protochlamydia amoebophila UWE25 and 4% in the Chlamydiaceae are most similar to chloroplastic, plant, and cyanobacterial genes. In 2006, an article noted L,L-diaminopimelate aminotransferase as remarkably similar to the plant and cyanobacterial versions.{{cite journal |vauthors=McCoy AJ, Adams NE, Hudson AO, Gilvarg C, Leustek T, Maurelli AT | title = L,L-diaminopimelate aminotransferase, a trans-kingdom enzyme shared by Chlamydia and plants for synthesis of diaminopimelate/lysine | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 103 | issue = 47 | pages = 17909–14 | year = 2006 | pmid = 17093042 | pmc = 1693846 | doi = 10.1073/pnas.0608643103 | bibcode = 2006PNAS..10317909M | doi-access = free }} An alternative, no less unusual interpretation from 2008 is that a Chlamydia might have been an endosymbioant of an ancestral plant, having transferring away some of its genes to the host before being lost.

Before the cyanobacterial hypothesis there were competing hypotheses involving Planctomycetota or Spirochaetota. The Planctomycetota theory has been present since 1987 with Cavalier-Smith's Planctobacteria.{{cite journal | last1 = Cavalier-Smith | first1 = T | year = 1987 | title = The origin of eukaryote and archaebacterial cells | journal = Annals of the New York Academy of Sciences | volume = 503 | issue = 1 | pages = 17–54 | doi=10.1111/j.1749-6632.1987.tb40596.x | pmid=3113314| bibcode = 1987NYASA.503...17C | s2cid = 38405158 }} This view was almost killed off by a 2000 study showing no significant link in 23S rRNA (just like earlier 16S rRNA analyses did).{{cite journal | vauthors = Ward NL, Rainey FA, Hedlund BP, Staley JT, Ludwig W, Stackebrandt E | title = Comparative phylogenetic analyses of members of the order Planctomycetales and the division Verrucomicrobia: 23S rRNA gene sequence analysis supports the 16S rRNA gene sequence-derived phylogeny | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 50 | issue = Pt 6 | pages = 1965–1972 | date = November 2000 | pmid = 11155969 | doi = 10.1099/00207713-50-6-1965 | doi-access = free }} James W. Molder, writing in 2003, believed that this represented the end of the Planctomycetes theory.{{cite web |last1=Moulder|first1=James W.|title=The first intracellular Chlamydiales. |url=http://chlamydiae.com/docs/Chlamydiales/ev_firstchlamydiales.asp |archive-url=https://web.archive.org/web/20101121031356/http://chlamydiae.com/docs/Chlamydiales/ev_firstchlamydiales.asp |archive-date=21 November 2010 }} However, growing evidence points to an actual link between these two phyla in what has since been known as the PVC superphylum.{{cite journal | vauthors = Teeling H, Lombardot T, Bauer M, Ludwig W, Glöckner FO | title = Evaluation of the phylogenetic position of the planctomycete 'Rhodopirellula baltica' SH 1 by means of concatenated ribosomal protein sequences, DNA-directed RNA polymerase subunit sequences and whole genome trees | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 54 | issue = Pt 3 | pages = 791–801 | date = May 2004 | pmid = 15143026 | doi = 10.1099/ijs.0.02913-0 | doi-access = free }}{{cite journal |last1=Rivas-Marín |first1=Elena |last2=Devos |first2=Damien P. |title=The Paradigms They Are a-Changin': past, present and future of PVC bacteria research |journal=Antonie van Leeuwenhoek |pages=785–799 |language=en |doi=10.1007/s10482-017-0962-z |date=1 June 2018|volume=111 |issue=6 |pmid=29058138 |pmc=5945725 }}{{Cite journal

| last1 = Wagner | first1 = M.

| last2 = Horn | first2 = M.

| doi = 10.1016/j.copbio.2006.05.005

| title = The Planctomycetes, Verrucomicrobia, Chlamydiae and sister phyla comprise a superphylum with biotechnological and medical relevance

| journal = Current Opinion in Biotechnology

| volume = 17

| issue = 3

| pages = 241–249

| year = 2006

| pmid = 16704931

}} Phylogeny and shared presence of CSIs in proteins that are lineage-specific indicate that the Verrucomicrobiota are the closest free-living relatives of these parasitic organisms as of 2007.{{cite journal | vauthors = Griffiths E, Gupta RS | title = Phylogeny and shared conserved inserts in proteins provide evidence that Verrucomicrobia are the closest known free-living relatives of chlamydiae | journal = Microbiology | volume = 153 | issue = Pt 8 | pages = 2648–2654 | date = August 2007 | pmid = 17660429 | doi = 10.1099/mic.0.2007/009118-0 | doi-access = free | s2cid = 2094762 }}

Comparison of ribosomal RNA genes has provided a phylogeny of known strains within Chlamydiota. Trees have since been built using more loci. See {{section link||Phylogeny}} below.

Three species of Chlamydiota that commonly infect humans are described:

• Chlamydia trachomatis, which causes the eye-disease trachoma and the sexually transmitted infection chlamydia
• Chlamydophila pneumoniae, which causes a form of pneumonia
• Chlamydophila psittaci, which causes psittacosis

The unique physiological status of the Chlamydiota including their biphasic lifecycle and obligation to replicate within a eukaryotic host has enabled the use of DNA analysis for chlamydial diagnostics.{{cite journal | vauthors = Corsaro D, Greub G | title = Pathogenic potential of novel Chlamydiae and diagnostic approaches to infections due to these obligate intracellular bacteria | journal = Clinical Microbiology Reviews | volume = 19 | issue = 2 | pages = 283–297 | date = April 2006 | pmid = 16614250 | pmc = 1471994 | doi = 10.1128/CMR.19.2.283-297.2006 }} Horizontal transfer of genes is evident and complicates this area of research. In one extreme example, two genes encoding histone-like H1 proteins of eukaryotic origin have been found in the prokaryotic genome of C. trachomatis, an obligate intracellular pathogen.

For the placement of taxa not found here, consult e.g. Gupta et al. (2015).

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN){{cite web | author=J.P. Euzéby | url=https://lpsn.dsmz.de/phylum/chlamydiota| title=Chlamydiota | access-date=2022-09-09 | publisher=List of Prokaryotic names with Standing in Nomenclature (LPSN)}} and National Center for Biotechnology Information (NCBI){{cite web |author = Sayers| url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Undef&id=204428&lvl=3&lin=f&keep=1&srchmode=1&unlock |title=Chlamydiae |access-date=2022-09-09 |publisher=National Center for Biotechnology Information (NCBI) taxonomy database |display-authors=et al.}}

• "Similichlamydiales" Pallen, Rodriguez-R & Alikhan 2022 [Hat2 GTDB]
• Family "Parilichlamydiaceae" Stride et al. 2013 ["Similichlamydiaceae" Pallen, Rodriguez-R & Alikhan 2022]
• Family "Piscichlamydiaceae" Horn 2010 – based on phylogeny in Gupta et al. (2015).{{cite journal |last1=Gupta |first1=Radhey S. |last2=Naushad |first2=Sohail |last3=Chokshi |first3=Chirayu |last4=Griffiths |first4=Emma |last5=Adeolu |first5=Mobolaji |title=A phylogenomic and molecular markers based analysis of the phylum Chlamydiae: proposal to divide the class Chlamydiia into two orders, Chlamydiales and Parachlamydiales ord. nov., and emended description of the class Chlamydiia |journal=Antonie van Leeuwenhoek |date=September 2015 |volume=108 |issue=3 |pages=765–781 |doi=10.1007/s10482-015-0532-1|pmid=26179278 }}
• Order Chlamydiales Storz & Page 1971
• Family "Actinochlamydiaceae" Steigen et al. 2013
• Family "Criblamydiaceae" Thomas, Casson & Greub 2006
• Family Chlamydiaceae Rake 1957
• Family Parachlamydiaceae Everett, Bush & Andersen 1999
• Family Rhabdochlamydiaceae Corsaro et al. 2009
• Family Simkaniaceae Everett, Bush & Andersen 1999
• Family Waddliaceae Rurangirwa et al. 1999

• List of bacterial orders
• List of bacteria genera

{{Reflist}}

• {{cite web | vauthors = Ward M | publisher = University of Southampton | title = www.chlamydiae.com | url = http://www.chlamydiae.com/restricted/default.asp | quote = The comprehensive reference and education wiki on Chlamydia and the Chlamydiales }}
• [https://www.stdcheck.com/chlamydia.php Chlamydia Overview ]

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Category:Bacteria phyla

Category:Monotypic bacteria taxa