Wikipedia

Chlamydiota

TheChlamydiota(synonymChlamydiae) are abacterialphylumandclasswhose members are remarkably diverse, includingpathogensof humans and animals,symbiontsof ubiquitousprotozoa,[4]and marine sediment forms not yet well understood.[5]All of the Chlamydiota that humans have known about for many decades are obligate intracellular bacteria; in 2020 many additional Chlamydiota were discovered in ocean-floor environments, and it is not yet known whether they all havehosts.[5]Historically it was believed that all Chlamydiota had apeptidoglycan-free cell wall, but studies in the 2010s demonstrated a detectable presence of peptidoglycan, as well as other important proteins.[6][7][8][9][10][11]

Chlamydiota
Chlamydia trachomatis
Scientific classificationEdit this classification
Domain: Bacteria
Superphylum: PVC superphylum
Phylum: Chlamydiota
Garrity & Holt 2021[3]
Class: Chlamydiia
Horn 2016[1][2]
Orders and families
Synonyms
  • Chlamydiota:
    • "Chlamydaeota"Oren et al. 2015
    • "Chlamydiae"Garrity and Holt 2001
    • "Chlamydiota"Whitman et al. 2018
    • "Chlamydobacteriae"Buchanan 1917
  • Chlamydiia:

Among the Chlamydiota, all of the ones long known to science grow only by infectingeukaryotichost cells. They are as small as or smaller than manyviruses.They are ovoid in shape and stainGram-negative.They are dependent on replication inside the host cells; thus, some species are termed obligateintracellular pathogensand others are symbionts of ubiquitous protozoa. Most intracellular Chlamydiota are located in aninclusion bodyorvacuole.Outside cells, they survive only as an extracellular infectious form.

These Chlamydiota can grow only where their host cells grow, and develop according to a characteristic biphasic developmental cycle.[12][13][14]Therefore,clinically relevantChlamydiotacannot be propagatedin bacterial culture media in the clinical laboratory. They are most successfully isolated while still inside their host cells.

Of various Chlamydiota that cause human disease, the two most important species areChlamydia pneumoniae,which causes a type ofpneumonia,andChlamydia trachomatis,which causeschlamydia.Chlamydia is the most common bacterialsexually transmitted infectionin the United States, and 2.86 million chlamydia infections are reported annually.

History

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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 andvon Prowazekin 1907.

Chlamydial isolates cultured in the yolk sacs of embryonating eggs were obtained from a humanpneumonitisoutbreak 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 trachomatiswas first cultured byTang Fei-fan,though they were not yet recognized as bacteria.[15]

Nomenclature

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In 1966, Chlamydiota were recognized as bacteria and the genusChlamydiawas validated.[16]The orderChlamydialeswas created by Storz and Page in 1971. The classChlamydiiawas recently validly published.[17][18][19]Between 1989 and 1999, new families, genera, and species were recognized. The phylum Chlamydiae was established inBergey's Manual of Systematic Bacteriology.[20]By 2006, genetic data for over 350 chlamydial lineages had been reported.[21]Discovery of ocean-floor forms reported in 2020 involves newclades.[5]In 2022 the phylum was renamed Chlamydiota.[3]

Taxonomy and molecular signatures

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The Chlamydiota currently contain eight validly named genera, and 14 genera.[22]The phylum presently consist of two orders (Chlamydiales, Parachlamydiales) and nine families within a single class (Chlamydiia).[17][18]Only four of these families are validly named (Chlamydiaceae,Parachlamydiaceae,Simkaniaceae,Waddliaceae)[23][24]while five are described as families (Clavichlamydiaceae,Criblamydiaceae,Parilichlamydiaceae,Piscichlamydiaceae,andRhabdochlamydiaceae).[25][26][27]

The Chlamydiales order as recently described contains the families Chlamydiaceae, and theClavichlamydiaceae,while the new Parachlamydiales order harbors the remaining seven families.[17]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 ofconserved 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.[17][28]The distinctness of the two orders is also supported by the fact that no CSIs were found among any other combination of families.

Molecular signatureshave also been found that are exclusive for the family Chlamydiaceae.[17][28]The Chlamydiaceae originally consisted of one genus,Chlamydia,but in 1999 was split into two genera,ChlamydophilaandChlamydia.The genera have since 2015 been reunited where species belonging to the genus Chlamydophila have been reclassified as Chlamydia species.[29][30]

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.[17][28]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.

Phylogenetics

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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.[17][28][31][14]The species from this group can be distinguished from all other bacteria by the presence of conservedindelsin a number of proteins and by large numbers of signature proteins that are uniquely present in different Chlamydiae species.[32][33]

Reports have varied as to whether the Chlamydiota are related to thePlanctomycetotaorSpirochaetota.[34][35]Genome sequencing, however, indicates that 11% of the genes inProtochlamydia amoebophilaUWE25 and 4% in the Chlamydiaceae are most similar tochloroplast,plant,andcyanobacterialgenes.[14]Cavalier-Smithhas postulated that the Chlamydiota fall into the clade Planctobacteria in the larger cladeGracilicutes.However, phylogeny and shared presence of CSIs in proteins that are lineage-specific indicate that theVerrucomicrobiotaare the closest free-living relatives of these parasitic organisms.[36]Comparison ofribosomal RNAgenes has provided aphylogenyof known strains within Chlamydiota.[21]

Human pathogens and diagnostics

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Three species of Chlamydiota that commonly infect humans are described:

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.[37]Horizontal transferof 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 obligateintracellular pathogen.

Phylogeny

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16S rRNA basedLTP_08_2023[38][39][40] 120 marker proteins basedGTDB08-RS214[41][42][43]
Chlamydiales
"Similichlamydiales"

"Parilichlamydiaceae"

Chlamydiales

Taxonomy

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The currently accepted taxonomy is based on theList of Prokaryotic names with Standing in Nomenclature(LPSN)[44]andNational Center for Biotechnology Information(NCBI)[45]

See also

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References

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