Calculibacillus koreensis gen. nov., sp. nov., an anaerobic Fe(III)-reducing bacterium isolated from sediment of mine tailings

A strictly anaerobic bacterium, strain B5^T, was isolated from sediment of an abandoned coal mine in Taebaek, Republic of Korea. Cells of strain B5^T were non-spore-forming, straight, Gram-positive rods. The optimum pH and temperature for growth were pH 7.0 and 30°C, respectively, while the strain was able to grow within pH and temperature ranges of 5.5–7.5 and 25–45°C, respectively. Growth of strain B5^T was observed at NaCl concentrations of 0 to 6.0% (w/v) with an optimum at 3.0–4.0% (w/v). The polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol, an unknown phospholipid and three unknown polar lipids. Strain B5^T grew anaerobically by reducing nitrate, nitrite, ferric-citrate, ferric-nitrilotriacetate, elemental sulfur, thiosulfate, and anthraquinone-2-sulfonate in the presence of proteinaceous compounds, organic acids, and carbohydrates as electron donors. The isolate was not able to grow by fermentation. Strain B5^T did not grow under aerobic or microaerobic conditions. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain B5^T is most closely related to the genus Tepidibacillus (T. fermentans STGH^T; 96.3%) and Vulcanibacillus (V. modesticaldus BR^T; 94.6%). The genomic DNA G+C content (36.9 mol%) of strain B5^T was higher than those of T. fermentans STGH^T (34.8 mol%) and V. modesticaldus BR^T (34.5 mol%). Based on its phenotypic, chemotaxonomic, and phylogenetic properties, we describe a new species of a novel genus Calculibacillus, represented by strain B5^T (=KCTC 15397^T =JCM 19989^T), for which we propose the name Calculibacillus koreensis gen. nov., sp. nov.