Sulfurospirillum oryzae sp. nov., A Novel Nitrogen-Fixing Bacterium Isolated from Paddy Soil.

An anaerobic, Gram-staining-negative, rod shaped, nitrogen-fixing strain designed SG202, was isolated from paddy soil collected from Fujian Province in China. Strain SG202 showed the highest 16S rRNA gene sequence similarity with the type strain Sulfurospirillum multivorans DSM 12446 (98.5%). Phylogenetic trees based on 16S rRNA gene sequences and conserved core genes from genomes indicated that strain SG202 branched with members of the genus Sulfurospirillum. Growth was observed at 25-37 °C (optimum 30 °C), pH 6.0-10.5 (optimum 7.5), and 0-0.6% (w/v) NaCl (optimum 0.2%). Strain SG202 contained MK-6 as the menaquinone and Cω7c (40.6%), C (33.3%), Cω7c (13.6%) and C (9.0%) as the major fatty acids. The genomic DNA G+C content was 39.0%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain SG202 and its closely related species S. multivorans DSM 12446, Sulfurospirillum halorespirans DSM 13726, Sulfurospirillum arsenophilum DSM 10659 and Sulfurospirillum diekertiae ACS were 81.3, 81.5, 84.4, 82.2% and 24.5, 24.5, 27.9, 25.2%, respectively. All these values were lower than the recommended species delineation thresholds of ANI (95-96%) and dDDH (70%). Strain SG202 possessed core genes (nifHDK) of nitrogen fixation, and nitrogenase activities (3470.45 μmol CH g protein h) was examined using the acetylene reduction assay. Based on the observed physiological properties, chemotaxonomic characteristics and genome analysis, strain SG202 is recognized as a novel species of the genus Sulfurospirillum, for which the name Sulfurospirillum oryzae sp. nov. is proposed. The type strain is SG202 (= GDMCC 1.3379= JCM 35596).