gen. nov., sp. nov., a thermophilic, autotrophic, sulfur-disproportionating deltaproteobacterium isolated from a hydrothermal pond.

A thermophilic, anaerobic, chemolithoautotrophic bacterium (strain Sh68) was isolated from a hydrothermal pond at Uzon Caldera, Kamchatka, Russia, using anoxic medium with elemental sulfur as the only energy source. Cells of strain Sh68 were Gram-stain-negative rods, 0.5-0.8 μm in diameter and 1.2-2.0 μm in length, motile by means of flagella. The temperature range for growth was 30-65 °C, with an optimum at 50-52 °C. The pH range for growth was 5.2-7.5, with optimum growth at pH 6.0-6.2. Growth of strain Sh68 was observed at NaCl concentrations ranging from 0 to 2.3 % (w/v). Strain Sh68 grew anaerobically with elemental sulfur as an energy source and bicarbonate/CO as a carbon source. Elemental sulfur was disproportionated to sulfide and sulfate. Growth was enhanced in the presence of poorly crystalline Fe(III) oxide (ferrihydrite) as a sulfide-scavenging agent. Strain Sh68 was also able to grow by disproportionation of thiosulfate and sulfite. Sulfate was not used as an electron acceptor either with H or with organic electron donors. Analysis of the 16S rRNA gene sequence revealed that the isolate belongs to the class and is related most closely to S69 (90.0 % similarity). On the basis of its physiological properties and results of phylogenetic analyses, strain Sh68 is considered to represent a novel species of a new genus, for which the name gen. nov., sp. nov. is proposed. The type strain of is Sh68 ( = JCM 19990 = VKM B-2854). This is the first description of a sulfur-disproportionating thermophile from a terrestrial ecosystem.