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Scientific classification
Domain: Bacteria
Phylum: Chlamydiae
Class: Chlamydiae
Order: Chlamydiales
Family: Chlamydiaceae
Genus: Chlamydophila

Chlamydophila is a bacterial genus belonging to the family Chlamydiaceae,[2] order Chlamydiales, class/phylum Chlamydiae.


Chlamydophila was recognized in 1999,[3] with six species in Chlamydophila and three in the original genus, Chlamydia. All Chlamydiae are anaerobic bacteria with a biphasic developmental lifecycle that depends on obligately intracellular growth in eukaryotic host cells.

Prior to 1999, criteria for chlamydial species were not exclusive. For example, at that time genus Chlamydia = family Chlamydiaceae; C. psittaci were distinguished from C. trachomatis by sulfadiazine resistance, although not all C. psittaci were resistant; C. pneumoniae was classified by its appearance under electron microscopy (EM) and its ability to infect humans, although the EM appearance was found to differ from one research group to the next, and all of these species infected humans.

The systematic taxonomy established for Chlamydiae in 1999 uses up-to-date, prevailing criteria for bacterial classification, including DNA-DNA reassociation, 16S and 23S ribosomal RNA gene similarity, sequence similarity clustering of protein coding genes, and genome size. Supporting criteria such as antigen detection,[4] glycogen staining, host association, and EM morphology are also employed, depending on applicability and availability. In 1999, many Chlamydia strains were reorganized into the genus Chlamydophila.

Comparative genomic analyses have identified large numbers of signature proteins that are uniquely present in species from the genera Chlamydia and Chlamydophila, supporting the distinctness of these genera.[5] This view has been challenged by a more recent whole genome analysis leading to a proposal to "reunite the Chlamydiaceae into a single genus, Chlamydia".[6] To date, this nomenclature controversy has not been resolved.[7]

Chlamydophila differentiation[edit]

The mean DNA-DNA reassociation similarity distinguishing Chlamydophila from Chlamydia is 10.1% (95% confidence interval = 6.8 through 13.5), an accepted value for genus separation.

Divergence of Chlamydophila from Chlamydia is indicated by sequence similarity clustering of protein coding and ribosomal RNA genes. The 16S ribosomal RNA gene sequences of Chlamydophila and Chlamydia are close to 95% identical. However, 95% is not a cutoff for separating Chlamydiaceae genera but is a guideline for establishing new genera in chlamydial families. The full-length 23S rRNA genes of Chlamydophila and Chlamydia species are less than 95% identical.

Some Molecular Criteria Distinguishing Chlamydiaceae Genera
Genus Approximate Genome Size (million DNA base pairs) Detectable Glycogen Number of Ribosomal Operons
Chlamydophila 1.2 No 1
Chlamydia 1.0 Yes 2


Distinctions such as EM morphology, antibiotic resistance, and extrachromosomal plasmid are typically species-specific characteristics.

Species in Chlamydophila include:


  1. ^ J.P. Euzéby. "Chlamydophila". List of Prokaryotic names with Standing in Nomenclature. Retrieved 2011-06-11. 
  2. ^ Chlamydophila at the US National Library of Medicine Medical Subject Headings (MeSH)
  3. ^ Everett KD, Bush RM, Andersen AA (April 1999). "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". Int. J. Syst. Bacteriol. 49 (2): 415–40. PMID 10319462. doi:10.1099/00207713-49-2-415. 
  4. ^ Bush RM, Everett KD (January 2001). "Molecular evolution of the Chlamydiaceae". Int. J. Syst. Evol. Microbiol. 51 (Pt 1): 203–20. PMID 11211261. 
  5. ^ Griffiths E, Ventresca MS, Gupta RS (2006). "BLAST screening of chlamydial genomes to identify signature proteins that are unique for the Chlamydiales, Chlamydiaceae, Chlamydophila and Chlamydia groups of species". BMC Genomics. 7: 14. PMC 1403754Freely accessible. PMID 16436211. doi:10.1186/1471-2164-7-14. 
  6. ^ Stephens RS, Myers G, Eppinger M, Bavoil PM (March 2009). "Divergence without difference: phylogenetics and taxonomy of Chlamydia resolved". FEMS Immunol. Med. Microbiol. 55 (2): 115–9. PMID 19281563. doi:10.1111/j.1574-695X.2008.00516.x. 
  7. ^ "Chlamydia/Chlamydophila group". NCBI taxonomy database. National Center for Biotechnology Information, U.S. National Library of Medicine. Retrieved 2013-03-26. Given the contentious nature of the issue, the NCBI Taxonomy Database retains both genus names for use by submitters. 

External links[edit]

  • Chlamydophila genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID
  • Taxonomic Outline of the Procaryotes, Bergey's Manual of Systematic Bacteriology, Second Edition Release 1.0, April c. [1]