Bacteria Genomes - CANDIDATUS PROTOCHLAMYDIA AMOEBOPHILA

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 to be a small group of a few closely related bacteria, characterised by a unique developmental cycle, which are well separated - both, biologically and phylogenetically - from all other known bacteria.

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 foetus has radically changed researchers' perception of chlamydial diversity and their distribution in nature. These findings resulted in the description of three novel families within the phylum Chlamydiae: Parachlamydiaceae, Simkaniaceae, and Waddliaceae.

Molecular data now suggests the existence of an additional, untold diversity of chlamydiae in the environment. Environmental chlamydiae naturally occur within phylogenetically different hosts but 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.

The increasing awareness of the diversity of chlamydiae and their distribution in the environment 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. Further studies and the inclusion of environmental chlamydiae in diagnostic assays are necessary to elucidate the role of environmental chlamydiae as potential emerging pathogens.

Strain UWE25, a symbiont of Acanthamoeba spp., was previously identified as being related to chlamydiae based upon the presence of a chlamydia-like developmental cycle and its 16S rRNA gene sequence. Analysis of its complete genome sequence demonstrated that UWE25 shows many characteristic features of chlamydiae, including dependency on host-derived metabolites, composition of the cell envelope and the ability to thrive as an energy parasite within the cells of its eukaryotic host.

References:

http://www.microbial-ecology.net/horn.asp
http://pathema.tigr.org/tigr-scripts/CMR/GenomePage.cgi?org=ntps03