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

Abstract

A thermophilic, anaerobic, chemolithoautotrophic bacterium (strain Sh68^T) 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^T 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^T was observed at NaCl concentrations ranging from 0 to 2.3 % (w/v). Strain Sh68^T grew anaerobically with elemental sulfur as an energy source and bicarbonate/CO₂ 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^T was also able to grow by disproportionation of thiosulfate and sulfite. Sulfate was not used as an electron acceptor either with H₂ or with organic electron donors. Analysis of the 16S rRNA gene sequence revealed that the isolate belongs to the class <i>Deltaproteobacteria</i> and is related most closely to <i>Dissulfuribacter thermophilus</i> S69^T (90.0 % similarity). On the basis of its physiological properties and results of phylogenetic analyses, strain Sh68^T is considered to represent a novel species of a new genus, for which the name <i>Dissulfurimicrobium hydrothermale</i> gen. nov., sp. nov. is proposed. The type strain of <i>Dissulfurimicrobium hydrothermale</i> is Sh68^T ( = JCM 19990^T = VKM B-2854^T). This is the first description of a sulfur-disproportionating thermophile from a terrestrial ecosystem.