Evidence for additional genus-level diversity of Chlamydiales in the environment

The medically important order Chlamydiales has long been considered to cont ain a few closely related bacteria which occur exclusively in animals and h umans. This perception of diversity and habitat had to be revised with the recent identification of the genera Simkania, Waddlia, Parachlamydia, and N eochlamydia with the latter two comprising endosymbionts of amoebae. Applic ation of a newly developed PCR assay for the specific amplification of a ne ar full length 16S rDNA fragment of these novel Chlamydia-related bacteria on activated sludge samples revealed the existence of at least four additio nal, previously unknown evolutionary lineages of Chlamydiales (each showing less than 92% 16S rRNA sequence similarity with all recognized members of this order). These findings suggest that some waste water treatment plants represent reservoirs for a diverse assemblage of environmental chlamydiae, a discovery which might also be of relevance from the viewpoint of human pu blic health. (C) 2001 Federation of European Microbiological Societies. Pub lished by Elsevier Science B.V. All rights reserved.