Bacteria of the Genus Sphaerochaeta from Low-Temperature Heavy Oil Reservoirs (Russia)

Abstract

Fermenting bacteria are usual components of oilfield microbial communities. Since pure cultures of fermenting bacteria utilize carbohydrates and do not grow on oil, their diversity and relationships in the community are of great interest. In the present work, enrichment and pure cultures of fermenting bacteria obtained from formation water of low-temperature oilfields (Russia) were studied. High-throughput sequencing of the V3–V4 region of the 16S rRNA gene was carried out for an enrichment culture. The library was found to contain the genes of anaerobic bacteria of the genus Halanaerobium, which are capable of growth on polysaccharides with thiosulfate reduction to sulfide, as well as the genes of Abyssivirga alkaniphila, which grows on C₅–C₂₅n-alkanes of oil with thiosulfate as an electron acceptor or in a syntrophic association with hydrogenotrophic methanogens. Members of the genus Sphaerochaeta were minor components of the community. Three strains (4-11, 5-8-5, and 17-50) were isolated from enrichment cultures. The isolates were anaerobic mesophilic slightly halophilic bacteria, which fermented a number of carbohydrates and grew as biofilms. The 16S rRNA gene sequences of the new strains exhibited 99.5–100% similarity between each other and 97.2–98.0% similarity to the sequences of the most closely related species Sphaerochaetaassociata and Sphaerochaetaglobosa, which indicated their affiliation to a new Sphaerochaeta species. The products of maltose fermentation were acetate, propionate, СО₂, Н₂, and sometimes iso-propanol. The strains did not grow on crude oil. In oilfields Sphaerochaeta species probably consume the products of oil biodegradation by other microorganisms, are involved in biofilms formation, and provide H₂ for methanogens and other components of the community.