Lessons from Environmental Chlamydiae

This chapter summarizes work on environmental chlamydiae performed primarily between 2008 and early 2011. The first studies on environmental chlamydiae reported the discoveries of Waddlia chondrophila, which was isolated from an aborted bovine fetus. Traditionally, chlamydial elementary bodies (EBs) are regarded as spore-like forms which are metabolically inert. The extracellular activity of chlamydial EBs was dependent on the incubation medium used, which may explain why EBs have not been previously shown to be metabolically active. A key feature of the natural host of many environmental chlamydiae, Acanthamoeba spp., is its ability to form cysts under adverse environmental conditions. For obligate intracellular bacteria like the chlamydiae, the term “host cell interactions” can be subdivided into the following temporally and spatially separated stages: microbe-host recognition, internalization, replicative phase with host cell exploitation, and finally persistence within or release from the host cell to start another infectious cycle. Environmental chlamydiae have been detected in a wide variety of vertebrate and invertebrate hosts, and some members of this group of bacteria have been proposed to cause disease in animals. Genomic comparison of environmental chlamydiae has revealed that Waddlia and Parachlamydia may be the most suitable chlamydial candidates for host-free cultivation, since these organisms have the most versatile biosynthetic capabilities among the chlamydiae.