DESULFURELLA KAMCHATKENSIS SP. NOV. AND DESULFURELLA-PROPIONICA SP. NOV., NEW SULFUR-RESPIRING THERMOPHILIC BACTERIA FROM KAMCHATKA THERMALENVIRONMENTS

Two strains of moderately thermophilic bacteria, which reduce elementa l sulfur to hydrogen sulfide, were isolated from volcanic sources in K amchatka. Strain K-119(T) was obtained from a thermophilic microbial c ommunity associated with Thermothrix thiopara, and strain U-8(T) was i solated from a cyanobacterial mat inhabiting a sulfide-rich hot spring . Cells of both strains are short Cram-negative rods, motile with one polar flagellum (strain K-119(T)) or non-motile (strain U-8(T)). Both strains are obligate anaerobes, have temperature optima of 54-55 degre es C and ph optima of 6.9-7.2. Molecular hydrogen, acetate, fumarate, malate, pyruvate, lactate and long-chain saturated fatty acids served as growth substrates for both species; strain U-8(T) was also able to grow on propionate. All substrates were oxidized completely, H2S and C O2 being the only metabolic products. Elemental sulfur was obligately required for growth of strain K-119(T), whereas strain U-8(T) was able to grow also with thiosulfate as electron acceptor and on pyruvate wi thout an external electron acceptor. The DNA G+C contents of strains K -119(T) and U-8(T) were 31.6 and 32.2 mol%, respectively. Phenotypic f eatures and the results of 16S rRNA sequencing indicate the affiliatio n of the new isolates to the genus Desulfurella. The DNA-DNA hybridiza tion with Desulfurella acetivorans was 40% for strain K-119(T) and 55% for strain U-8(T); the DNA-DNA hybridization between the new isolates was 32%. Based on the results of morphological. physiological and phy logenetic studies the following two new species are proposed: Desulfur ella kamchatkensis sp. nov. with the type strain K-119(T) (= DSM 10409 (T)) and Desulfurella propionica sp. nov. with the type strain U-8(T) (= DSM 10410(T)).