Cauispirillum nitrogeniifigens gen. nov., sp. nov., a new member of the family Rhodospirillaceae isolated from oil sludge

The high carbon to nitrogen ratio in oil-contaminated environments limits the efficiency of bioremediation. Therefore, isolating nitrogen-fixing bacteria from oil-contaminated environments will provide functional strain resources for improving bioremediation efficiency. A novel Gram-stain-negative, spiral-shaped and nitrogen-fixing bacterium, designated strain DQ9^T, was isolated from the oil sludge of Daqing Oilfield, Daqing City, Heilongjiang Province, China. Cells grew at 18-45 °C (optimum of 40 °C), at pH of 6.5-9.0 (optimum of 7.0) and with 0-2.0% (w/v) NaCl (optimum of 0%). The respiratory quinone was ubiquinone 8 (Q-8). The major cellular fatty acids were summed feature 8 (C_18:1 <i> ω7c</i> and/or C_18:1 <i> ω6c</i>) (46.8%), summed feature 3 (C_16:1 <i>ω7c</i> and/or C_16:1 <i> ω6c</i>) (14.6%) and C_16:0 (17.4%). The polar lipids consisted of phosphatidylglycerol (PG), phosphatidylethanolamine (PE), an unidentified aminophospholipid (UAPL), an unidentified aminolipid (UAL) and two unidentified lipids (UL1-2). Strain DQ9^T exhibited the highest 16S rRNA gene sequence similarities with <i>Novispirillum itersonii</i> subsp. <i>itersonii</i> LMG 4337^T (94.10%), <i>N. itersonii</i> subsp. <i>nipponicum</i> LMG 7370^T (94.10%), <i>Marispirillum indicum</i> B142^T (94.04%) and <i>Caenispirillum bisanense</i> K92^T (93.44%). The genomic DNA G+C content was 69.8 mol%. Comparing strain DQ9^T with closely related type strains, the digital DNA-DNA hybridization values were 18.5-22.0%, the average nucleotide identity values based on blast+ were 67.88-73.76%, the average amino acid identity values were 58-62% and the percentage of conserved proteins values were 45.53-58.80%. In the phylogenetic trees based on 16S rRNA genes and whole-genome sequences, strain DQ9^T formed an independent branch within the family <i>Rhodospirillaceae</i>. Based on the results of phylogenetics, morphology, physiology and chemotaxonomy, strain DQ9^T represents a novel species of a novel genus in the family <i>Rhodospirillaceae</i>, for which the name <i>Cauispirillum nitrogeniifigens</i> gen. nov., sp. nov. is proposed. The type strain is DQ9^T (=KCTC 8951^T=CGMCC 1.65428^T).