Acidisoma tundrae gen. nov., sp nov and Acidisoma sibiricum sp nov., two acidophilic, psychrotolerant members of the Alphaproteobacteria from acidic northern wetlands

Three obligately aerobic, heterotrophic bacteria, designated strains WM1(T) TPB606(T) and TPB621, were isolated from acidic Sphagnum-dominated tundra and Siberian wetlands in Russia. Cells of these isolates were Gram-negative, non-motile coccobacilli that occurred singly, in pairs or in chains, and were covered by large capsules. The novel strains were moderately acidophilic and psychrotolerant organisms capable of growth at pH 3.0-7.6 and 2-30 degrees C. Cells contained numerous intracellular poly-beta-hydroxybutyrate granules (3-4 per cell). The major cellular fatty acid was cyclo C-19:0 omega 8c and the predominant quinone was Q-10. Strains TPB606(T) and TPB621, isolated from Siberian wetland, possessed almost identical 16S rRNA gene sequences and shared 97.2% sequence similarity with tundra strain WM1(T). The three strains were shown to belong to the Alphaproteobacteria, but were related only distantly to the type strains of acidophilic bacteria Acidisphaera rubrifaciens (93.4-94.3% 16S rRNA gene sequence similarity), Rhodopila globiformis (92.2-93.3%), and members of the genera Acidiphilium (91.3-93%) and Acidocella (91.8-92.4%). The DNA G + C contents of the novel strains were 60.5-61.9 mol%. The low levels of DNA-DNA relatedness (37%) and a number of phenotypic differences between the Siberian strains TPB606(T) and TPB621 and the tundra strain WM1(T) indicated that they represent two separate species. As the three isolates are clearly distinct from all recognized acidophilic members of the Alphaproteabacteria, they are considered to represent two novel species of a new genus, for which the names Acidisoma tundrae gen. nov., sp. nov. and Acidisoma sibiricum sp. nov. are proposed. The type strain of Acidisoma sibiricum, is TPB606(T) (= DSM 21000(T) = VKM B-2487(T)) and the type strain of Acidisoma tundrae is WM1(T) (= DSM 19999(T) = VKM B-2488(T)).