Thermophilic Bacteria in Lake Baikal Bottom Sediments Associated with Hydrocarbon Discharge

— The research was aimed at detection of thermophilic microorganisms in Lake Baikal low-temperature sediments associated with discharge of gas-saturated fluids. Members of the order Clostridiales were revealed in enrichment cultures obtained from the bottom sediments at three sites (methane seep, oil-methane seep, and mud volcano) . No thermophilic prokaryotes were found in the enrichment culture with sediment samples from a background area. The presence of thermophilic microorganisms at the sites of hydrocarbon discharge may result from their migration to the bottom surface with the gas-bearing mineralized fluid moving along the fracture zones. Unlike marine cold sediments, where the endospores of thermophilic bacteria belong to strict anaerobes existing due to fermentation of organic substrates or sulfate reduction, Lake Baikal sediments associated with discharge of gas-saturated fluids were found to contain facultatively anaerobic thermophilic prokaryotes.