Biodiversity of Anaerobic lithotrophic prokaryotes in terrestrial hot springs of Kamchatka

Terrestrial hot springs in Kamchatka with different temperatures (55-90 deg rees C) and acidity (pH 2.0-8.5) were screened for the presence of thermoph ilic microorganisms responsible for different anaerobic lithotrophic proces ses: methanogenesis, acetogenesis, sulfate and sulfur reduction, anaerobic oxidation of CO, reduction of ferric iron, and nitrate reduction. In additi on to radioisotopic experiments in situ with C-14-bicarbonate, the potentia l capacity of samples to perform various anaerobic processes was detected b y the formation of reduced products or by utilization of energy substrates in the presence of electron accepters. Lithotrophic methanogenesis was foun d to occur at alkaline and neutral pH, in the former case only at 60-70 deg rees C, whereas sulfidogenesis was observed at neutral and acidic pH in the whole temperature range studied. Lithotrophic acetogenesis was observed in the entire range of pH values; in an acidic environment, its rate increase d with temperature. Anaerobic carboxydotrophs were found only at neutral pH and at temperatures of 55-70 degrees C. Lithotrophic reduction of Fe(III) occurred at all pH and temperature values studied, but the optimum was at 6 0 degrees C and neutral pH. From the same samples, enrichment and pure cult ures of thermophilic lithotrophic anaerobes with new combinations of phenot ypic characteristics were obtained.