Rhodanobacter denitrificans sp. nov., isolated from nitrate-rich zones of a contaminated aquifer

Bacterial strains 2APBS1^T and 116-2 were isolated from the subsurface of a nuclear legacy waste site where the sediments are co-contaminated with large amounts of acids, nitrate, metal radionuclides and other heavy metals. A combination of physiological and genetic assays indicated that these strains represent the first member of the genus Rhodanobacter shown to be capable of complete denitrification. Cells of strain 2APBS1^T and 116-2 were Gram-negative, non-spore-forming rods, 3–5 µm long and 0.25–0.5 µm in diameter. The isolates were facultative anaerobes, and had temperature and pH optima for growth of 30 °C and pH 6.5; they were able to tolerate up to 2.0 % NaCl, although growth improved in its absence. Strains 2APBS1^T and 116-2 contained fatty acid and quinone (ubiquinone-8; 100 %) profiles that are characteristic features of the genus Rhodanobacter. Although strains 2APBS1^T and 116-2 shared high 16S rRNA gene sequence similarity with Rhodanobacter thiooxydans LCS2^T (>99 %), levels of DNA–DNA relatedness between these strains were substantially below the 70 % threshold used to designate novel species. Thus, based on genotypic, phylogenetic, chemotaxonomic and physiological differences, strains 2APBS1^T and 116-2 are considered to represent a single novel species of the genus Rhodanobacter, for which the name Rhodanobacter denitrificans sp. nov. is proposed. The type strain is 2APBS1^T ( = DSM 23569^T = JCM 17641^T).