Diversity of Thermophilic Prokaryotes Inhabiting Russian Natural Hot Springs

Abstract: In this review, we highlight the key results of studies on the diversity of thermophilic prokaryotes inhabiting the Russian Federation’s hot springs. The main part of the review is a summary of the results obtained from several decades of research on the thermophilic microbial communities of the Kamchatka Peninsula, the Kuril Islands, and Lake Baikal using classical microbiological approaches, radioisotopic tracing, and molecular ecology. Apart from these well-studied environments, we have also included recent exploration of the hot springs located in the East-Tuvinian upland, the Chukchi Peninsula, Sakhalin, and the North Caucasus. First, we discuss taxonomy of all above-mentioned thermophilic prokaryotes. Second, we consider the main energy-providing processes, based primarily on redox reactions of inorganic (mainly sulfur and iron) and organic compounds. Then, we discuss in detail the thermophilic prokaryotes involved in the carbon cycle: from CO₂-assimilating chemolithoautotrophs to heterotrophs capable of hydrolyzing complex organic matter. Last, we discuss uncultivated lineages of thermophilic bacteria and archaea, which are present or even predominant in the thermal environments.