Chlamydiota

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Chlamydiota
Chlamydia trachomatis
Scientific classification Edit 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:
    • Chlamydiae
      Cavalier-Smith
      2002
    • "Chlamydozoa" Moshkovskiy 1945

The Chlamydiota (synonym Chlamydiae) are a

phylum and class whose members are remarkably diverse, including pathogens of humans and animals, symbionts of ubiquitous protozoa,[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 have hosts.[5] Historically it was believed that all Chlamydiota had a peptidoglycan-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]

Among the Chlamydiota, all of the ones long known to science grow only by infecting

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
. 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 relevant Chlamydiota cannot be propagated in 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 are Chlamydia pneumoniae, which causes a type of pneumonia, and Chlamydia trachomatis, which causes chlamydia. Chlamydia is the most common bacterial sexually transmitted infection in the United States, and 2.86 million chlamydia infections are reported annually.

History

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

Tang Fei-fan, though they were not yet recognized as bacteria.[15]

Nomenclature

In 1966, Chlamydiota were recognized as bacteria and the genus

Chlamydiia was recently validly published.[17][18][19] Between 1989 and 1999, new families, genera, and species were recognized. The phylum Chlamydiae was established in Bergey'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 new clades.[5] In 2022 the phylum was renamed Chlamydiota.[3]

Taxonomy and molecular signatures

The Chlamydiota currently contain eight validly named genera, and 14 genera.

Rhabdochlamydiaceae).[25][26][27]

The Chlamydiales order as recently described contains the families Chlamydiaceae, and the Clavichlamydiaceae, 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 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.[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 signatures have 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, Chlamydophila and Chlamydia. 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

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 conserved indels in 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 the

phylogeny of known strains within Chlamydiota.[21]

Human pathogens and diagnostics

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.

intracellular pathogen
.

Phylogeny

16S rRNA based
LTP_08_2023[38][39][40]
 120 marker proteins based GTDB 08-RS214[41][42][43]
Chlamydiales
"Similichlamydiales"

"Parilichlamydiaceae"

Chlamydiales

Simkaniaceae

"

Rhabdochlamydiaceae
"

Waddliaceae

"Criblamydiaceae"

Parachlamydiaceae

Chlamydiaceae

Taxonomy

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

See also

References

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  22. ^ Sayers; et al. "Chlamydiia". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2016-10-24.
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  38. ^ "The LTP". Retrieved 20 November 2023.
  39. ^ "LTP_all tree in newick format". Retrieved 20 November 2023.
  40. ^ "LTP_08_2023 Release Notes" (PDF). Retrieved 20 November 2023.
  41. ^ "GTDB release 08-RS214". Genome Taxonomy Database. Retrieved 10 May 2023.
  42. ^ "bac120_r214.sp_label". Genome Taxonomy Database. Retrieved 10 May 2023.
  43. ^ "Taxon History". Genome Taxonomy Database. Retrieved 10 May 2023.
  44. ^ J.P. Euzéby. "Chlamydiota". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved 2022-09-09.
  45. ^ Sayers; et al. "Chlamydiae". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2022-09-09.

External links

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