Thermanaerovibrio velox sp nov., a new anaerobic, thermophilic, organotrophic bacterium that reduces elemental sulfur, and emended description of the genus Thermanaerovibrio

A moderately thermophilic, organotrophic bacterium with vibrioid cells was isolated from a sample of a cyanobacterial mat from caldera Uzon, Kamchatka, Russia, and designated strain Z-9701(T). Cells of strain Z-9701(T) were curved, Gram-negative rods, 0.5-0.7 x 2.5-5.0 mu m in size, with tapering ends and with fast, wavy movement by means of lateral flagella located on the concave side of the cell. Colonies were small, white, irregular or round, 0.2 mm in diameter, and with even edges. Strain Z-9701(T) was an obligate anaerobe with a temperature optimum at 60-65 degrees C and a pH optimum at 7.3. It fermented glucose, fructose, mannose, N-acetyl-D-glucosamine, adonite, arginine, serine, peptone, yeast extract and Casamino acids. The fermentation products formed during growth on glucose were acetate, lactate, H-2, CO2 and ethanol. Strain Z-9701(T) reduced elemental sulfur to H2S during organotrophic growth with glucose or peptides as energy and carbon sources. In the presence of S-0, strain Z-9701(T) was capable of lithotrophic growth with molecular hydrogen as energy substrate and 0.1 g yeast extract l(-1) as carbon source. Sulfate, thiosulfate, nitrate, Fe(III) and sulfite were not reduced and did not stimulate growth. The G+C content of strain Z-9701(T) DNA was 54.6 mol%. The results of 16S rDNA sequence analyses revealed that strain Z-9701(T) belongs to the cluster within the Clostridium group formed by Thermanaerovibrio acidaminovorans, Dethiosulfovibrio peptidovorans, Anaerobaculum thermoterrenum and Aminobacterium colombiense, but the level of sequence similarity with the members of this cluster was not very high (87.6-92.2%). Among these organisms, Thermanaerovibrio acidaminovorans is phenotypically close to strain Z-9701(T). However. the two organisms showed ii relatively low level of similarity of their 16S rRNA sequences (92.2%) and of DNA-DNA hybridization (15+/-1%). Nevertheless, on the basis of the similar morphology and physiology of the new isolate and Thermanaerovibrio acidaminovorans, strain Z-9701(T) was placed in the genus Thermanaerovibrio and a new species, Thermanaerovibrio velox, proposed for it. The type strain is Z-9701(T) (= DSM 12556(T)).