Chlamydiae

Chlamydiae
Chlamydia trachomatis
Scientific classification
Domain:	Bacteria
Phylum:	Chlamydiae
Class:	Chlamydiae Cavalier-Smith 2002
Order:	Chlamydiales Storz and Page 1971 emend. Everett et al. 1999
Families
?Candidatus Parilichlamydia carangidicola Stride et al. 2013 ?Candidatus Piscichlamydia Draghi et al. 2004 Criblamydiaceae Criblamydia ♠ Thomas et al. 2006 Estrella ♠ Thomas et al. 2006 Candidatus Rhabdochlamydiaceae Candidatus Renichlamydia Corsaro and Work 2012 Candidatus Rhabdochlamydia Kostanjsek et al. 2004 Chlamydiaceae Rake 1957 emend. Everett et al. 1999 Candidatus Amphibiichlamydia Martel et al. 2012 Candidatus Clavochlamydia Karlsen et al. 2008 Chlamydia Jones et al. 1945 emend. Everett et al. 1999 Chlamydophila Everett et al. 1999 Parachlamydiaceae Everett et al. 1999 Candidatus Mesochlamydia Corsaro et al. 2012 Candidatus Metachlamydia Corsaro et al. 2010 Protochlamydia ♠ Collingro et al. 2005 Neochlamydia Horn et al. 2001 Parachlamydia Everett et al. 1999 Simkaniaceae Everett et al. 1999 Simkania Everett et al. 1999 Candidatus Fritschea Everett et al. 2005 Waddliaceae Rurangirwa et al. 1999 Waddlia Rurangirwa et al. 1999

Chlamydiae is a bacterial phylum and class whose members are obligate intracellular pathogens. They are ovoid in shape. They have a peptidoglycan-free cell wall and are susceptible to various antimicrobial agents. All known chlamydiae only grow by infecting eukaryotic host cells. They are as small as or smaller than many viruses. Chlamydiae replicate inside the host cells and are termed intracellular. Most intracellular chlamydiae are located in an inclusion body or vacuole. Outside of cells they survive only as an extracellular infectious form. Chlamydiae can grow only where their host cells grow. Therefore, chlamydiae cannot be propagated in bacterial culture media in the clinical laboratory. Chlamydiae are most successfully isolated while still inside their host cell.

Cavalier-Smith has postulated that the Chlamydiae fall into the clade Planctobacteria in the larger clade Gracilicutes.

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 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.

Nomenclature

In 1966, chlamydiae were recognized as bacteria and the genus Chlamydia was validated. The order Chlamydiales was created by Storz and Page in 1971. Between 1989 and 1999, new families, genera, and species were recognized. The phylum Chlamydiae was established in Bergey's Manual of Systematic Bacteriology.

By 2006, genetic data for over 350 chlamydial lineages had been reported, four chlamydial families had been recognized (Chlamydiaceae, Parachlamydiaceae, Simkaniaceae, and Waddliaceae), and another family had been proposed (Rhabdochlamydiaceae).

Genomics

The chlamydiae form a unique bacterial evolutionary group that separated from other bacteria approximately a billion years ago. The species from this group can be distinguished from all other bacteria by the presence of conserved indels in a number of proteins such as RNA polymerase alpha subunit, Gyrase B, Elongation factor-Tu and Elongation factor-P, and by large numbers of signature proteins that are uniquely present in different chlamydiae species. Reports have varied as to whether chlamydiae is related to Planctomycetales or Spirochaetes. Genome sequencing, however, indicates that 11% of the genes in Candidatus Protochlamydia amoebophila UWE25 and 4% in Chlamydiaceae are most similar to chloroplast, plant, and cyanobacterial genes. However, phylogeny and shared presence of conserved indels in proteins such as RNA polymerase Beta subunit and lysyl-tRNA synthetase indicate that Verrucomicrobia are the closest free-living relatives of these parasitic organisms. Comparison of ribosomal RNA genes has provided a phylogeny of known strains within chlamydiae. The unique status of chlamydiae has enabled the use of DNA analysis for chlamydial diagnostics.

There are three described species of chlamydiae that commonly infect humans:

• 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.

Phylogeny

See also: Bacterial taxonomy

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and the phylogeny is based on 16S rRNA-based LTP release 111 by The All-Species Living Tree Project

?Candidatus Parilichlamydia carangidicola Stride et al. 2013 ?Candidatus Piscichlamydia salmonis Draghi et al. 2004 ?Criblamydiaceae ♠ Criblamydia sequanensis ♠ Thomas et al. 2006 Estrella lausannensis ♠ ?Candidatus Rhabdochlamydiaceae Candidatus Renichlamydia lutjani Corsaro and Work 2012 ?Candidatus Rhabdochlamydia Candidatus R. crassificans (Radek 2000) Corsaro et al. 2007 Candidatus R. porcellionis Kostanjsek et al. 2004 Waddlia W. chondrophila Rurangirwa et al. 1999 W. malaysiensis ♥ Chua et al. 2005 Simkaniaceae Simkania negevensis Everett et al. 1999 Candidatus Fritschea Candidatus F. bemisiae Everett et al. 2005 Candidatus F. eriococci Everett et al. 2005 Parachlamydiaceae ?Candidatus Mesochlamydia elodeae Corsaro et al. 2012 ?Candidatus Metachlamydia lacustris Corsaro et al. 2010 ?Protochlamydia ♠ Candidatus P. amoebophila Collingro et al. 2005 P. naegleriophila ♠ Casson et al. 2006 Neochlamydia hartmannellae Horn et al. 2001 Parachlamydia acanthamoebae Everett et al. 1999 Chlamydiaceae ?Candidatus Amphibiichlamydia Candidatus A. ranarum Martel et al. 2013 Candidatus A. salamandrae Martel et al. 2012 ?Candidatus Clavochlamydia salmonicola Karlsen et al. 2008 Chlamydophila pneumoniae (Grayston et al. 1989) Everett et al. 1999 Chlamydophila C. psittaci (Lillie 1930) Everett et al. 1999 C. felis Everett et al. 1999 C. caviae Everett et al. 1999 C. abortus Everett et al. 1999 Chlamydophila pecorum (Fukushi and Hirai 1992) Everett et al. 1999 Chlamydia C. muridarum Everett et al. 1999 C. suis Everett et al. 1999 C. trachomatis (Busacca 1935) Rake 1957 emend. Everett et al. 1999

Notes:
♠ Strains found at the National Center for Biotechnology Information (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature (LSPN) ♥ Strains not lodged at National Center for Biotechnology Information (NCBI) and or listed in the List of Prokaryotic names with Standing in Nomenclature (LPSN)

External links

• Chlamydiae.com, a comprehensive information source from Dr. Michael Ward (Professor of Medical Microbiology in the University of Southampton)