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 ω7c and/or C 18:1 ω6c ) (46.8%), summed feature 3 (C 16:1 ω7c and/or C 16:1 ω6c ) (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 Novispirillum itersonii subsp. itersonii LMG 4337 T (94.10%), N. itersonii subsp. nipponicum LMG 7370 T (94.10%), Marispirillum indicum B142 T (94.04%) and Caenispirillum bisanense 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 Rhodospirillaceae . Based on the results of phylogenetics, morphology, physiology and chemotaxonomy, strain DQ9 T represents a novel species of a novel genus in the family Rhodospirillaceae , for which the name Cauispirillum nitrogeniifigens gen. nov., sp. nov. is proposed. The type strain is DQ9 T (=KCTC 8951 T =CGMCC 1.65428 T ).