Isolation and characterization of Methanoculleus receptaculi sp nov from Shengli oil field, China

Three strictly anaerobic, thermophilic methanogens (ZC-2(T), ZC-3 and ZC-6) were isolated from Shengli oil field, China. The 16S rRNA gene sequences of the three strains were nearly identical, possessing > 99.8% sequence similarity. They also possessed high sequence similarity, 97.4%, to Methanoculleus palmolei strain INSLUZ(T) (97.4% and 97.5%, respectively), indicating that they represented a novel species within the genus Methanoculleus. Cells of strain ZC-2(T) were nonmotile cocci, 0.8-1.7 mu m in diameter, and always occurred singly or in pairs. The three strains used H(2)/CO(2) or sodium formate as substrates for methanogenesis but not sodium acetate, trimethylamine, monomethylamine, ethanol, dimethyl sulfide, isopropanol, isobutanol, butan-2-ol or H(2)/CO. Optimum growth of strain ZC-2(T) occurred in the presence of 0.2 M NaCl, pH 7.5-7.8 and temperature 50-55 degrees C with a specific growth rate of 0.084 h(-1). The mol% G+C content of the genomic DNA was 55.2 mol%. Based on these phenotypic and phylogenetic characteristics, strains ZC-2(T), ZC-3 and ZC-6 are proposed to represent a novel species in the genus Methanoculleus and named Methanoculleus receptaculi sp. nov. The type strain is ZC-2(T) (CGMCC 1.5087(T)=DSM 18860(T)).