Abstract
A new extremely thermophilic, anaerobic, obligately carboxydotrophic, chemolithoautotrophic freshwater bacterium, strain Z-2901, was isolated from a hot swamp of Kunashir Island. This isolate is characterized by a novel type of chemotrophic metabolism. It grows rapidly on CO (100% CO in the gas phase) as sole carbon and energy source with the production of equimolar quantities of H2 according to the equation CO + H2O → H2 + CO2. Other products are not formed and other inorganic and organic substrates are not used. Growth temperatures are between 40 and 78°C with an optimum at 70–72°C. The pH optimum is 6.8–7.0. The generation time under optimal conditions is 120 min. The cells of the new isolate are Gram-positive non-sporeforming short rods with an S-layer. They often occur in pairs, chains and aggregates and are motile by one or two lateral flagella. The GC-content of the DNA is 39.0 mol%. Growth and CO-utilization are inhibited by penicillin, chloramphenicol and streptomycin (100 μg/ml). On the basis of its unique physiological features and thermophilic nature of the new bacterium the isolate is proposed to represent a new genus, Carboxydothermus with the type species C. hydrogenoformans; the type strain is Z-2901 (DSM 6008).
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