Description of Demequina pilifera sp. nov. and Demequina ureilytica sp. nov. isolated from a mixture of oil production fluids in Shengli Oilfield.

Abstract

Two novel strains, designated SO4-18^T and SO4-13^T, were isolated from a mixture of oil production fluid sourced from Shengli Oilfield in China. Cells of the isolates were Gram-stain-positive, facultatively anaerobic, non-motile and piliated. Growth occurred at 4-37 °C (optimum 30 °C), pH 6.0-9.0 (optimum pH 8.0) and up to 0-13% (w/v) NaCl (optimum 1% and 1-2%, respectively). Phylogenetic analysis based on the 16S rRNA gene sequence, combined with genome-based investigations, revealed that the two isolates belong to the genus Demequina, and their 16S rRNA gene sequences shared less than 98.61% similarity with valid members in this genus. The average nucleotide identities, average amino acid identity and digital DNA-DNA hybridization values, whether between the two isolates or between either isolate and the type strains of other Demequina species, were all well beneath the established thresholds for species delineation. Pan-genomic analysis indicated that strains SO4-18^T and SO4-13^T shared ranges from 360 to 1,706 core gene clusters compared to other members of the genus Demequina. Chemotaxonomic characterization revealed the major polar lipids of the isolates, including diphosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannosides, glycolipids and aminolipid, whereas the number and composition of unidentified lipids differed between the two isolates. The predominant fatty acids (>10% of the total content) were anteiso-C_15 : 0, C_16 : 0, anteiso-C_17 : 0 and anteiso-C_15 : 0 A, with menaquinone DMK-9(H₄) as the major respiratory quinones for both isolates. Based on the comprehensive phenotypic and genotypic characterizations presented in this study, strains SO4-18^T and SO4-13^T are proposed to represent two novel species of the genus Demequina, for which the names Demequina pilifera sp. nov. and Demequina ureilytica sp. nov. are proposed. The type strains of Demequina pilifera sp. nov. and Demequina ureilytica are SO4-18^T (=CGMCC 1.16447^T=KCTC 59404^T) and SO4-13^T (=CGMCC 1.16448^T=KCTC 59689^T), respectively.