New Thermophilic Microorganisms Isolated From Extreme Environments

Quite a few microorganisms have been discovered in extreme environments such as hydrothermal vents, hot springs and deep subsurface environments, but a large number of extremophiles in these environments have still remained uncultured. We are searching for those unknown organisms hidden in extreme environments. In our attempts, we have successfully isolated several new extremophiles. One of the isolates, Thermanaeromonas toyohensis, is a spore-forming strictly anaerobic bacterium growing at 70°C in subsurface environments. Its most unique property is that it can use formate, the simplest organic acid, as a sole energy and carbon source in the presence of a suitable electron sink. Formate can be synthesized abiotically in thermal subsurface environments. The ability to use formate is advantageous for living in those subsurface environments that lack more complex organic compounds. Another isolate, Thermodesulfobium narugense, is a thermophilic sulfate-reducing bacterium isolated from a Japanese hot spring (Narugo hot spring in Miyagi). The bacterium is not phylogenetically related to any known sulfate-reducers, and we have proposed a new family, Thermodesulfobiaceae, for the isolate. This isolate occupies an interesting and important phylogenetic position in considering an evolutionary pathway of sulfate-reduction that has remained mysterious. The other isolate, Oceanithermus desulfurans, was found in a deep-sea hydrothermal vent. The new isolate is a thermophilic short rod which grows well under micro-aerobic conditions (less than 5% oxygen tension). It can also grow by reducing sulfur under anaerobic conditions. Generally, Thermus relatives do not use sulfur as an electron acceptor. This is the first report on sulfur-reduction by a Thermus-related species. We also succeeded in isolating a new thiosulfate-reducing archaeon from a hydrothermal vent. The phylogenetic analysis indicated that the isolate belongs to the genus Archaeoglobus, and should be classified as a new species in the genus. The new archaeon may play a significant role in the deep-sea sulfur cycle with other thermophilic sulfur reducers and oxidizers.