Anoxygenic phototrophic bacteria from extreme environments

Abstract

Anoxygenic phototrophic bacteria have conquered various types of habitats of extreme conditions of temperature, pH and salinity. A short overview is given on the species found, on the properties of their extreme habitats and their phylogenetic relations. Hot spring habitats include springs from the USA, Russia, Japan, Tibet, Greenland with the Yellowstone hot springs being the most prominent and best studied. Chloroflexus aurantiacus occurring worldwide in hot springs is tolerant to the highest temperatures up to 70 °C. Cold adapted phototrophic bacteria forms have been studied in Antarctic fjords and lakes and in sea ice with an example from the Baltic Sea. Chlorobaculum tepidum and Rhodopila globiformis are prominent examples of the small number of phototrophic bacteria adapted to acidic pH. Though anoxygenic phototrophic bacteria are prominent inhabitants of alkaline soda lakes within the whole range of salt concentrations, only a few groups have successfully conquered this type of habitats. Most widely distributed and diverse are the representatives of phototrophic as well as chemotrophic Ectothiorhodospiraceae. These form often massive colored developments in shallow waters and sediments. Different types of phototrophic purple bacteria inhabit hypersaline coastal lagoons, salterns and salt lakes. Purple sulfur bacteria with prominent representatives of Halochromatium and Thiohalocapsa species and purple nonsulfur bacteria with Rhodovibrio, Rhodothalassium species are regularly found in microbial mats occurring in these habitats. A short review is also included on mechanisms of adaptation to high temperatures and salt concentrations.