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.

Abstract

Anaerobic, fermentative, halotolerant bacteria, strains 4-11Tand 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 4-11Tgrew 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 C14:0, C16:0, C16:1ω9 and C18:03-OH. Major polar lipids were glycolipids and phospholipids. The 16S rRNA gene sequences of the strains 4-11Tand 585 had 99.9% similarity and were most closely related to the sequence ofSphaerochaeta associataGLS2T(96.9, and 97.0% similarity, respectively). The G+C content of the genomic DNA of strains 4-11Tand 585 were 46.8 and 46.9%, respectively. The average nucleotide identity and digital DNA–DNA hybridization values between the genomes of strain 4-11TandS. associataGLS2Twere 73.0 and 16.9%, respectively. Results of phylogenomic metrics analysis of the genomes and 120 core proteins of strains 4-11Tand 585 and their physiological and biochemical characteristics confirmed that the strains represented a novel species of the genusSphaerochaeta, for which the nameSphaerochaeta halotoleranssp. nov. is proposed, with the type strain 4-11T(=VKM B-3269T=KCTC 15833T). Based on the results of phylogenetic analysis,Sphaerochaeta coccoideswas reclassified as member of a new genusParasphaerochaetagen. nov.,Parasphaerochaeta coccoidescomb. nov. The generaSphaerochaetaandParasphaerochaetaform a separate clade, for which a novel family,Sphaerochaetaceaefam. nov., is proposed.