Environmental Chlamydiae
Chlamydiae as we knew them
Chlamydiae are perhaps the most successful obligate intracellular bacterial pathogens, representing the world's major cause of preventable blindness and sexually transmitted disease. Until about a decade ago chlamydiae were considered a small group of few closely related bacteria deeply branching within the domain Bacteria, characterized by a unique developmental cycle, and thus being well separated - both, biologically and phylogenetically - from all other known bacteria.
The unexpected diversity of chlamydiae
The discovery of chlamydiae as symbionts of free-living amoebae or insects, as pathogens of crustaceans, as contaminants of a laboratory cell culture, and in an aborted bovine fetus radically changed our perception of chlamydial diversity and their distribution in nature (Kahane et al., 1995; Amann et al., 1997; Rurangirwa et al., 1999; Horn et al., 2000; Thao et al., 2003; Kostanjsek et al., 2004; Draghi et al., 2004). These findings resulted in the description of three novel families within the phylum Chlamydiae: Parachlamydiaceae, Simkaniaceae, and Waddliaceae (Rurangirwa et al., 1999; Everett et al., 1999). Moreover, molecular data suggest the existence of an additional, untold diversity of chlamydiae in the environment (Ossewaared et al., 1999; Horn et al., 2001; Corsaro et al., 2003). The extent of the diversity of environmental chlamydiae thus by far exceeds the diversity of previously recognized pathogenic chlamydiae.
"How do you know it's chlamydia?"
Environmental chlamydiae naturally occur within phylogenetically different hosts (amoebae vs. humans) than pathogenic chlamydiae. However, it seems convincing that their designation as "chlamydiae" is well justified. Environmental chlamydiae show the same obligate intracellular life style as pathogenic chlamydiae, and the morphology of their developmental stages is highly similar in ultrastructure to the elementary and reticulate bodies of pathogenic chlamydiae. Most importantly, environmental chlamydiae are more closely related to pathogenic chlamydiae than to any other bacteria, thus representing the closest living relatives of pathogenic chlamydiae. It is therefore likely that a more detailed analysis of the only recently identified environmental chlamydiae will reveal further similarities with pathogenic chlamydiae, making environmental chlamydiae a suitable model system to study chlamydial biology.
Implications for public health
The increasing awareness of the diversity of chlamydiae and their distribution in the environment also deserves attention from a public health point of view. Several lines of evidence indicate a possible association of the only recently recognized environmental chlamydiae with respiratory disease of humans (Greub et al., 2002). First, elevated antibody titers against Simkania or Parachlamydia were detected in patients with respiratory disease of unknown cause. Second, 16S rRNA genes that are more similar to rRNA genes of environmental chlamydiae than to rRNA genes of pathogenic chlamydiae were found in clinical specimen from respiratory disease patients. Third, parachlamydiae, which naturally thrive within amoebae, have been demonstrated to be able to enter and multiply in human cells including macrophages and epithelial cells (Greub et al., 2003; Collingro et al., 2005). Taken together, it seems conceivable that environmental chlamydiae have simply been overlooked as possible cause for respiratory disease. Therefore, additional studies and the inclusion of environmental chlamydiae in diagnostic assays are necessary to elucidate the role of environmental chlamydiae as potential emerging pathogens.
[This text was modified from an abstract published in "Proceedings of the 5th Meeting of the European Society for Chlamydia Research", Budapest, September 2004.]
Investigated by:  Matthias Horn, Astrid Collingro, Stephan Schmitz-Esser,
Eva Heinz, Susanne Haider, Elena Tönshoff, Christian Heinz, Irina Kolarov,
Jacqueline Montanaro
Links:
Environmental chlamydia genomics and post-genomics
Nucleotide transport proteins in environmental chlamydiae
Review on environmental chlamydiae (at Michael E. Ward's www.chlamydiae.com)
'Candidatus Piscichlamydia salmonis' - editorial at Michael E. Ward's www.chlamydiae.com)
References
- Amann, R., Springer, N., Schonhuber, W., Ludwig, W., Schmid, E. N., Muller, K. D., and Michel, R. (1997). Obligate intracellular bacterial parasites of acanthamoebae related to chlamydia spp. Appl Environ Microbiol 63, 115-121.
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- Collingro A, Poppert S, Heinz E, Schmitz-Esser S, Essig A, Schweikert M, Wagner M, Horn M. (2005). Recovery of an environmental chlamydia strain from activated sludge by co-cultivation with Acanthamoeba sp. Microbiology 151, 301-309.
- Corsaro, D., Valassina, M., and Venditti, D. (2003). Increasing diversity within chlamydiae. Crit Rev Microbiol 29, 37-78.
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- Draghi, A., 2nd, Popov, V. L., Kahl, M. M., Stanton, J. B., Brown, C. C., Tsongalis, G. J., West, A. B. & Frasca, S., Jr. (2004). Characterization of "Candidatus piscichlamydia salmonis" (order Chlamydiales), a chlamydia-like bacterium associated with epitheliocystis in farmed Atlantic salmon (Salmo salar). J Clin Microbiol 42, 5286-5297.
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- Everett, K. D., Bush, R. M., and Andersen, A. A. (1999a). 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, 415-440.
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- Greub, G., and Raoult, D. (2002). Parachlamydiaceae: potential emerging pathogens. Emerg Infect Dis 8, 625-630.
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- Greub, G., Mege, J.-L., and Raoult, D. (2003d). Parachlamydia acanthamoeba Enters and Multiplies within Human Macrophages and Induces Their Apoptosis. Infect Immun 71, 5979-5985.
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- Horn, M., Wagner, M., Muller, K. D., Schmid, E. N., Fritsche, T. R., Schleifer, K. H., and Michel, R. (2000). Neochlamydia hartmannellae gen. nov., sp. nov. (Parachlamydiaceae), an endoparasite of the amoeba Hartmannella vermiformis. Microbiology 146, 1231-1239.
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- Horn, M., and Wagner, M. (2001). Evidence for additional genus-level diversity of Chlamydiales in the environment. FEMS Microbiol Lett 204, 71-74.
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- Kahane, S. E. M., and Friedman, M. G. (1995). Evidence that the novel microorganism 'Z' may belong to a new genus in the family Chlamydiaceae. FEMS Microbiol Lett 126, 203-208.
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- Kostanjsek, R., Strus, J., Drobne, D. & Avgustin, G. (2004). 'Candidatus Rhabdochlamydia porcellionis', an intracellular bacterium from the hepatopancreas of the terrestrial isopod Porcellio scaber (Crustacea: Isopoda). Int J Syst Evol Microbiol 54, 543-549.
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- Ossewaarde, J. M., and Meijer, A. (1999). Molecular evidence for the existence of additional members of the order Chlamydiales. Microbiology 145, 411-417.
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- Rurangirwa, F. R., Dilbeck, P. M., Crawford, T. B., McGuire, T. C., and McElwain, T. F. (1999). Analysis of the 16S rRNA gene of microorganism WSU 86-1044 from an aborted bovine foetus reveals that it is a member of the order Chlamydiales: proposal of Waddliaceae fam. nov., Waddlia chondrophila gen. nov., sp. nov. Int J Syst Bacteriol 49, 577-581.
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- Thao, M. L., Baumann, L., Hess, J. M., Falk, B. W., Ng, J. C., Gullan, P. J., and Baumann, P. (2003). Phylogenetic evidence for two new insect-associated Chlamydia of the family Simkaniaceae. Curr Microbiol 47, 46-50.
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