A thermophilic, anaerobic, spore-forming, dissimilatory Fe(lll)-reducing bacterium, designated strain SR4, was isolated from sediment of newly formed hydrothermal vents in the area of the eruption of Karymsky volcano on the Kamchatka peninsula. Cells of strain SR4 were straight-to-curved, peritrichous rods, 0.4-0.6 μ in diameter and 3.5-9.0 μ in length, and exhibited a slight tumbling motility. Strain SR4 formed round, refractile, heatresistant endospores in terminally swollen sporangia. The temperature range for growth was 39–78 °C with an optimum at 69–71 °C. The pH range for growth was 4.8-8.2, with an optimum at 6.3-6.5. Strain SR4 grew anaerobically with peptone as carbon source. Amorphous iron(lll) oxide present in the medium stimulated the growth of strain SR4; cell numbers increased with the concomitant accumulation of Fe(ll). In the presence of Fe(lll), strain SR4 grew on H/CO and utilized molecular hydrogen. Strain SR4 reduced 9,10-anthraquinone-2,6-disulfonic acid, sulfite, thiosulfate, elemental sulfur and MnO. Strain SR4 did not reduce nitrate or sulfate and was not capable of growth with O. The fermentation products from glucose were ethanol, lactate, H and CO The G+C content of DNA was 32 mol%. 16S rDNA sequence analysis placed the organism in the genus . On the basis of physiological properties and phylogenetic analysis, it is proposed that strain SR4 (= DSM 12299) should be assigned to a new species, sp. nov.


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