Filamentous anoxygenic phototrophic bacteria in water bodies of Middle and Lower Volga basin (European Russia): an overview

“Filamentous anoxygenic phototrophs” or “green non-sulfur bacteria” form a distinct lineage, order Chloroflexales (Chloroflexia: Chloroflexi) in broad polyphyletic group of anoxygenic phototrophic bacteria. Filamentous anoxygenic phototrophic bacteria have apparently important, though not fully understood functions in contemporary ecosystems and perhaps were much more significant in the Archaean. However, since their discovery in hot spring mats in the late 1960s, the extremophilic species of thermal, hypersaline and/or hyperalcaline habitats remain the most studied representatives of the lineage. In this overview, we show our representation of the history of finding and research of filamentous anoxygenic phototrophs, and current situation with their taxonomy, phylogeny and diversity. Some problems and uncertainties in these fields are also discussed. The special section is dedicated to the discovery and research of this group in the Volga River basin. Due to the small number of studies, the exact distribution of filamentous anoxygenic phototrophic bacteria in the region is unknown. For example, in small stratified lakes with high humic and/or ferruginous water in the basins of the Oka and the Upper Volga the development of planktonic filamentous anoxygenic phototrophs is very likely. Besides, the development of Chloroflexales, including new species, is quite expected in the microbial mats of saline rivers and hypersaline lakes of the Lower Volga region. Further progress in the field will be possible only with the use of molecular methods along or preferably in combination with traditional methods (polyphasic approach). Since their role in communities is far from elucidated, further studies of FAP may also provide new opportunities in the field of microbial biotechnology.