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

Abstract

A strictly anaerobic bacterium, strain B5T, was isolated from sediment of an abandoned coal mine in Taebaek, Republic of Korea. Cells of strain B5T 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 B5T 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 B5T 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 B5T did not grow under aerobic or microaerobic conditions. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain B5T is most closely related to the genus Tepidibacillus (T. fermentans STGHT; 96.3%) and Vulcanibacillus (V. modesticaldus BRT; 94.6%). The genomic DNA G+C content (36.9 mol%) of strain B5T was higher than those of T. fermentans STGHT (34.8 mol%) and V. modesticaldus BRT (34.5 mol%). Based on its phenotypic, chemotaxonomic, and phylogenetic properties, we describe a new species of a novel genus Calculibacillus, represented by strain B5T (=KCTC 15397T =JCM 19989T), for which we propose the name Calculibacillus koreensis gen. nov., sp. nov.