[Methanocalculus natronophilus sp. nov., a new alkaliphilic hydrogenotrophic methanogenic archaeon from a soda lake, and proposal of the new family Methanocalculaceae].

A mesophilic hydrogenotrophic methanogenic archaeon, strain Z-7105(T), was isolated from the bottom sediments of a collector in the vicinity of a soda lake Tanatar II (Altai, Russia). The cells were motile, irregular cocci 0.2-1.2 µm in diameter. The organism was an obligate alkaliphile, growing within a pH range from 8.0 to 10.2 with the optimum at pH 9.0-9.5. It was obligately dependent on carbonates, growing at 0.5 to 1.6 M total carbonates with the optimum at 0.7-0.9 M. Sodium ions were also obligately required at concentrations from 0.9 to 3.3 M Na+ (optimum at 1.4-1.9 M). The organism was halotolerant, but Cl- ions were not required. Hydrogen and formate were used as electron donors. Acetate was required for anabolism. The DNA G + C content was 50.2 mol %. According to the results of its 16S rRNA gene sequence analysis, the isolate belonged to the genus Methanocalculus, being the first known alkaliphilic member of this genus. Its similarity to the neutrophilic and halotolerant Methanocalculus species (M. halotolerans, M. taiwanensis, M. pumilus, and M. chunghsingensis) was 98.2-97.1%, which is within the interspecific range for this genus. The level of DNA-DNA hybridization between strain Z-7105(T) and the Methanocalculus type species M. halotolerans DSM 14092(T) was 32%. The genus Methanocalculus, including the new isolate and the previously described species, is distant from other genera of methanogens (< 90% 16S rRNA gene similarity). Based on significant phenotypic differences and the results of phylogenetic analysis, including DNA-DNA hybridization, it is proposed to assign strain Z-7105(T) (= DSM 25006(T), = VKM B-2765(T)) to the new species Methanocalculus natronophilus sp. nov. and to incorporate the genus into the new family Methanocalculaceae fam. nov.

[The new facultatively chemolithoautotrophic, moderately halophilic, sulfate-reducing bacterium Desulfovermiculus halophilus gen. nov., sp. nov., isolated from an oil field].

The new mesophilic, chemolithoautotrophic, moderately halophilic, sulfate-reducing bacterium strain 11-6 could grow at a NaCl concentration in the medium of 30-230 g/l, with an optimum at 80-100 g/l. Cells were vibrios motile at the early stages of growth. Lactate, pyruvate, malate, fumarate, succinate, propionate, butyrate, crotonate, ethanol, alanine, formate, and H2 + CO2 were used in sulfate reduction. Butyrate was degraded completely, without acetate accumulation. In butyrate-grown cells, a high activity of CO dehydrogenase was detected. Additional growth factors were not required. Autotrophic growth occurred, in the presence of sulfate, on H2 + CO2 or formate without other electron donors. Fermentation of pyruvate and fumarate was possible in the absence of sulfate. Apart from sulfate, sulfite, thiosulfate, and elemental sulfur were able to serve as electron acceptors. The optimal growth temperature was 37 degrees C; the optimum pH was 7.2. Desulfoviridin was not detected. Menaquinone MK-7 was present. The DNA G+C content was 55.2 mol %. Phylogenetically, the bacterium represented a separate branch within the cluster formed by representatives of the family Desulfohalobiaceae in the subclass Deltaproteobacteria. The bacterium was assigned to a new genus and species, Desulfovermiculus halophilus gen. nov., sp. nov. The type strain is 11-6T (= VKM B-2364), isolated from the highly mineralized formation water of an oil field.