Sphaerochaeta halotolerans sp. nov., a novel spherical halotolerant spirochete from a Russian heavy oil reservoir, emended description of the genus Sphaerochaeta, reclassification of Sphaerochaeta coccoides to a new genus Parasphaerochaeta gen. nov. as Parasphaerochaeta coccoides comb. nov. and proposal of Sphaerochaetaceae fam. nov.
Salimat K. Bidzhieva, Diyana Sh. Sokolova, Denis S. Grouzdev, Nadezhda A. Kostrikina, А. Б. Полтараус, T. P. Tourova, V. A. Shcherbakova, Olga Troshina, Tamara N. Nazina
Abstract
Anaerobic, fermentative, halotolerant bacteria, strains 4-11 T and 585, were isolated from production water of two low-temperature petroleum reservoirs (Russia) and were characterized by using a polyphasic approach. Cells of the strains were spherical, non-motile and 0.30–2.5 µm in diameter. Strain 4-11 T grew optimally at 35 °C, pH 6.0 and 1.0–2.0% (w/v) NaCl. Both strains grew chemoorganotrophically with mono-, di- and trisaccharides. The major cellular fatty acids of both strains were C 14:0 , C 16:0 , C 16:1 ω9 and C 18:0 3-OH. Major polar lipids were glycolipids and phospholipids. The 16S rRNA gene sequences of the strains 4-11 T and 585 had 99.9% similarity and were most closely related to the sequence of Sphaerochaeta associata GLS2 T (96.9, and 97.0% similarity, respectively). The G+C content of the genomic DNA of strains 4-11 T and 585 were 46.8 and 46.9%, respectively. The average nucleotide identity and digital DNA–DNA hybridization values between the genomes of strain 4-11 T and S. associata GLS2 T were 73.0 and 16.9%, respectively. Results of phylogenomic metrics analysis of the genomes and 120 core proteins of strains 4-11 T and 585 and their physiological and biochemical characteristics confirmed that the strains represented a novel species of the genus Sphaerochaeta , for which the name Sphaerochaeta halotolerans sp. nov. is proposed, with the type strain 4-11 T (=VKM B-3269 T =KCTC 15833 T ). Based on the results of phylogenetic analysis, Sphaerochaeta coccoides was reclassified as member of a new genus Parasphaerochaeta gen. nov., Parasphaerochaeta coccoides comb. nov. The genera Sphaerochaeta and Parasphaerochaeta form a separate clade, for which a novel family, Sphaerochaetaceae fam. nov., is proposed.