gen. nov., sp. nov., an anaerobic formate-utilizing bacterium isolated from Shengli oilfield, and proposal of four novel families and ord. nov. in the phylum .

A novel obligately anaerobic, thermophilic and formate-utilizing bacterium K32 was isolated from Shengli oilfield of China. Cells were straight rods (0.4-0.8 µm × 2.5-8.0 µm), Gram-stain-positive, non-spore-forming and slightly motile. Optimum growth occurred with pH of 7 and 0.5 g l NaCl under temperature of 55-60 °C. Nitrate could be reduced into nitrite, syntrophic formate oxidation to methane and carbon dioxide occurred when co-culturing strain K32 and ΔH. The main cellular fatty acids were iso-C (24.0 %), anteiso-C (21.7 %), C (12.7 %) and C (10.8 %), and the main polar lipid was phosphatidylglycerol. The G+C content of the genomic DNA was 46.3 mol%. The 16S rRNA gene sequence of K32 shared ≤90.4 % of sequence similarity to closest type strains of , and members of the genus . Based on the phenotypic, biochemical and genotypic characterization, gen. nov., sp. nov. is proposed with K32 (=CCAM 584 =DSM 107278=CGMCC1.5297) as the type strain, which is the first representative of fam. nov. In addition, the order nd family were reclassified, and three novel families in the novel order of ord. nov. were also proposed.