Azotosporobacter soli gen. nov., sp. nov., a novel nitrogen-fixing bacterium isolated from paddy soil.

A nitrogen-fixing strain designated SG130 was isolated from paddy soil in Fujian Province, China. Strain SG130 was Gram-staining-negative, rod-shaped, and strictly anaerobic. Strain SG130 showed the highest 16S rRNA gene sequence similarities with the type strains Dendrosporobacter quercicolus DSM 1736 (91.7%), Anaeroarcus burkinensis DSM 6283 (91.0%) and Anaerospora hongkongensis HKU 15 (90.9%). Furthermore, the phylogenetic and phylogenomic analysis also suggested strain SG130 clustered with members of the family Sporomusaceae and was distinguished from other genera within this family. Growth of strain SG130 was observed at 25-45 °C (optimum 30 °C), pH 6.0-9.5 (optimum 7.0) and 0-1% (w/v) NaCl (optimum 0.1%). The quinones were Q-8 and Q-9. The polar lipids were phosphatidylserine (PS), phosphatidylethanolamine (PE), glycolipid (GL), phospholipid (PL) and an unidentified lipid (UL). The major fatty acids (> 10%) were iso-C 3OH (26.6%), iso-C (15.6%) and iso-C F (11.4%). The genomic DNA G + C content was 50.7%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain SG130 and the most closely related type strain D. quercicolus DSM 1736 (ANI 68.0% and dDDH 20.3%) were both below the cut-off level for species delineation. The average amino acid identity (AAI) between strain SG130 and the most closely related type strain D. quercicolus DSM 1736 was 63.2%, which was below the cut-off value for bacterial genus delineation (65%). Strain SG130 possessed core genes (nifHDK) involved in nitrogen fixation, and nitrogenase activity (106.38 μmol CH g protein h) was examined using the acetylene reduction assay. Based on the above results, strain SG130 is confirmed to represent a novel genus of the family Sporomusaceae, for which the name Azotosporobacter soli gen. nov., sp. nov. is proposed. The type strain is SG130 (= GDMCC 1.3312 = JCM 35641).