Enrichment and isolation of acid-tolerant sulfate-reducing microorganisms in the anoxic, acidic hot spring sediments from Copahue volcano, Argentina.
The geothermal Copahue-Caviahue (GCC) system (Argentina) is an extreme acidic environment, dominated by the activity of the Copahue volcano. Environments characterized by low pH values, such as volcanic areas, are of particular interest for the search of acidophilic microorganisms with application in biotechnological processes. In this work, sulfate-reducing microorganisms were investigated in geothermal acidic, anaerobic zones from GCC system. Sediment samples from Agua del Limón (AL1), Las Máquinas (LMa2), Las Maquinitas (LMi) and Baño 9 (B9-2, B9-3) were found to be acidic (pH values 2.1-3.0) to moderate acidic (5.1-5.2), containing small TOC values, and ferric iron precipitates. The organic electron donor added to the enrichments was completely oxidized to CO2. Bacteria related to 'Desulfobacillus acidavidus' strain CL4 were found to be dominant (67-83% of the total number of clones) in the enrichment cultures, and their presence was confirmed by their isolation on overlay plates. Other bacteria were also detected with lower abundance (6-20% of the total number of clones), with representatives of the genera Acidithiobacillus, Sulfobacillus, Alicyclobacillus and Athalassotoga/Mesoaciditoga. These enrichments and isolates found at low pH confirm the presence of anaerobic activities in the acidic sediments from the geothermal Copahue-Caviahue system.