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

A nitrogen-fixing strain designated SG130^T was isolated from paddy soil in Fujian Province, China. Strain SG130^T was Gram-staining-negative, rod-shaped, and strictly anaerobic. Strain SG130^T showed the highest 16S rRNA gene sequence similarities with the type strains Dendrosporobacter quercicolus DSM 1736^T (91.7%), Anaeroarcus burkinensis DSM 6283^T (91.0%) and Anaerospora hongkongensis HKU 15^T (90.9%). Furthermore, the phylogenetic and phylogenomic analysis also suggested strain SG130^T clustered with members of the family Sporomusaceae and was distinguished from other genera within this family. Growth of strain SG130^T 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_13:0 3OH (26.6%), iso-C_17:1 (15.6%) and iso-C_15:1 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^T and the most closely related type strain D. quercicolus DSM 1736^T (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^T and the most closely related type strain D. quercicolus DSM 1736^T was 63.2%, which was below the cut-off value for bacterial genus delineation (65%). Strain SG130^T possessed core genes (nifHDK) involved in nitrogen fixation, and nitrogenase activity (106.38 μmol C₂H₄ g^-1 protein h^-1) was examined using the acetylene reduction assay. Based on the above results, strain SG130^T 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^T (= GDMCC 1.3312^T = JCM 35641^T).