Genomic and Physiological Characterization of Halophilic Bacteria of the Genera Halomonas and Marinobacter from Petroleum Reservoirs

During the exploitation of oil reservoirs with highly mineralized waters, water separated from oil is pumped back into the reservoirs, which in some cases leads to an increase in ambient salinity and limits the possibility of application of biotechnologies for the enhancement of oil recovery. The microbial community of such oil fields has been relatively scarcely studied. Two strains of halophilic hydrocarbon-oxidizing bacteria, Halomonas titanicae TAT1 and Marinobacter lutaoensis KAZ22 were isolated from oil fields with mineralized formation water. Their physiological and genomic characteristics determining their presence in these habitats and the possibility of biotechnological application were investigated. The strains H. titanicae TAT1 and M. lutaoensis KAZ22 grew aerobically on crude oil in the temperature range from 4 to 42 and from 22 to 55°C, respectively, and had growth optima at salinity levels of 2–12 and 5–10% NaCl (wt/vol). Phenomenological observations of the degradation of oil n-alkanes were confirmed by the detection of three genes (alkB1, alkB2, and almA) encoding alkane1-monooxygenases in the genome of strain KAZ22 and of one alkB gene in the genome of strain TAT1. In the genome of the H. titanicae TAT1, all the genes for formation of osmoprotectants betaine, ectoine, and hydroxyectoine were annotated, and in the genome of M. lutaoensis KAZ22, the genes for the formation of ectoine and hydroxyectoine were annotated. The growth of strain KAZ22 on oil was accompanied by a decrease in the surface tension of the medium by more than 20 mN/m. Due to the absence of the nirK nitrite reductase gene, anaerobic growth of strain H. titanicae TAT1 in a medium with acetate and nitrate resulted in accumulation of ~100 mg/L of nitrite, which can inhibit the growth of sulfidogens. Considering the biological features of the strains and the results of genome analysis, injection of nitrate and strain H. titanicae TAT1 can be recommended for bioaugmentation of oil reservoirs with mineralized formation waters to suppress corrosion and decrease sulfide content, and injection of M. lutaoensis KAZ22, for remediation of oil pollution and increasing oil recovery from reservoirs.