Chlamydial biology and cell biology

A general review of chlamydial biology can be found in reference 1. The past few years have witnessed significant inroads into the understanding of how chlamydiae modify the intracellular environment to facilitate growth. Attachment is proposed to be mediated by surface proteins including possibly the major outer membrane protein [MOMP: 2,3] and/or the 60 kDal cysteine rich protein [4, 5], and/or one of the members of the Pmp family of proteins [6] in a heparin-dependent process [7, 8]. Chlamydial MOMP is the major serovariant molecule within chlamydial species. C. trachomatis strains can be grouped into approximately 18 serovars and sub-serovars, including serovars A-K and L1, L2, L3. There are biological differences within the species that can be generally organized by serovar, including aggressiveness of disease, tissue tropism, and certain properties of the interaction between bacteria and host cells [9-11].

There has been considerable recent progress in the area of chlamydial inclusion biogenesis (reviewed in [12-14]). These studies collectively support a model in which the chlamydiae are able to direct the modification of what is initially an endocytic vacuole – the phagosome – into a vacuole that receives material perhaps through a diverse set of vesicle trafficking pathways [15-17]. Treatment of infected cells with chloramphenicol or tetracycline (Tet) blocks inclusion development at a very early stage, indicating this process is dependent on chlamydial protein synthesis [18]. Chlamydial effectors that participate in the establishment of the replication vacuole are both present on the inclusion membrane [19, 20] and secreted into the cytosol of infected cells [21]. There are many different proteins present on the chlamydial inclusion membrane (Inc proteins), the majority of which are not functionally characterized. One Inc protein, IncA, is responsible for homotypic vesicle fusion in host cells infected with multiple C. trachomatis EBs [22-24]. Our laboratories showed that individuals infected with IncA-negative “nonfusogenic” strains were associated with a less symptomatic infection and shed lower numbers of chlamydiae [25]. IncA-negative strains occur in between 1.5 and 2% of C. trachomatis positive patients in Seattle area STD clinics [23]. 

Our laboratories have worked with the biology of Inc proteins for several years, with a goal of understanding the way Inc proteins participate in the establishment of the chlamydial intracellular niche [19, 20, 22]. Recently we have also explored a unique host protein, known as adducin, as it is recruited to the inclusion membrane within infected cells [24].

This is an area of chlamydial biology that has seen, and will continue to see, significant progress. Our website will likely not keep up with this progress, so make sure you check the recent literature to stay current in this area. Keywords linked to “chlamydia” for searches might include “cell biology, rab proteins, inclusion membrane proteins”.



1. Abdelrahman YM, Belland RJ. The chlamydial developmental cycle. FEMS Microbiol Rev 2005;29:949-959
2. Su H, Watkins NG, Zhang YX and Caldwell HD. Chlamydia trachomatis-host cell interactions: role of the chlamydial major outer membrane protein as an adhesin. Infect Immun 1990;58:1017-1025
3. Su H, Raymond L, Rockey DD, Fischer E, Hackstadt T and Caldwell HD. A recombinant Chlamydia trachomatis major outer membrane protein binds to heparan sulfate receptors on epithelial cells. Proc Natl Acad Sci U S A 1996;93:11143-11148
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13. Rockey DD, Alzhanov D. Proteins in the chlamydial inclusion membrane. In: Bavoil P, and Wyrick, P., ed. Chlamydia: Genomics and Pathogenesis. Norfolk, U.K.: Horizon Press, 2006
14. Valdivia RH. Chlamydia effector proteins and new insights into chlamydial cellular microbiology. Curr Opin Microbiol 2008;11:53-59
15. Kumar Y, Cocchiaro J and Valdivia RH. The obligate intracellular pathogen Chlamydia trachomatis targets host lipid droplets. Curr Biol 2006;16:1646-1651
16. Beatty WL. Trafficking from CD63-positive late endocytic multivesicular bodies is essential for intracellular development of Chlamydia trachomatis. J Cell Sci 2006;119:350-359
17. Hackstadt T, Scidmore MA and Rockey DD. Lipid metabolism in Chlamydia trachomatis-infected cells: directed trafficking of Golgi-derived sphingolipids to the chlamydial inclusion. Proc Natl Acad Sci U S A 1995;92:4877-4881
18. Scidmore MA, Rockey DD, Fischer ER, Heinzen RA and Hackstadt T. Vesicular interactions of the Chlamydia trachomatis inclusion are determined by chlamydial early protein synthesis rather than route of entry. Infect Immun 1996;64:5366-5372
19. Bannantine JP, Griffiths RS, Viratyosin W, Brown WJ and Rockey DD. A secondary structure motif predictive of protein localization to the chlamydial inclusion membrane. Cell Microbiol 2000;2:35-47
20. Rockey DD, Scidmore MA, Bannantine JP and Brown WJ. Proteins in the chlamydial inclusion membrane. Microbes Infect 2002;4:333-340
21. Zhong G, Fan P, Ji H, Dong F and Huang Y. Identification of a chlamydial protease-like activity factor responsible for the degradation of host transcription factors. J Exp Med 2001;193:935-942
22. Hackstadt T, Scidmore-Carlson MA, Shaw EI and Fischer ER. The Chlamydia trachomatis IncA protein is required for homotypic vesicle fusion. Cell Microbiol 1999;1:119-130
23. Suchland RJ, Rockey DD, Bannantine JP and Stamm WE. Isolates of Chlamydia trachomatis that occupy nonfusogenic inclusions lack IncA, a protein localized to the inclusion membrane. Infect Immun 2000;68:360-367.
24. Suchland, R.J., D.D. Rockey, S. Weeks, D. Alzhanov, and W.E. Stamm. Development of secondary inclusions by Chlamydia trachomatis. Infection and Immunity 2005; 73: 3954-3962.
25. Chu, H.G., S. K. Weeks, D. M. Gilligan, and D. D. Rockey. Host -adducin is redistributed and localized to the inclusion membrane in Chlamydia- and Chlamydophila-infected cells. Microbiology 2008; 154:3848-3855 2008.