Novel Aerobic Methylotrophic Isolates from the Soda Lakes of the Southern Transbaikal Region

Twenty-one bacterial associations isolated from the soda lakes of the southern Transbaikal region were found to be able to actively grow at pH 9–10 on methanol as the source of carbon and energy. Two alkalitolerant facultatively methylotrophic strains, Bur 3 and Bur 5, were obtained in pure cultures. Both strains represent gram-negative, nonmotile, bean-shaped, encapsulated cells that reproduce by binary fission. The strains are able to grow at temperatures ranging from 6 to 42°C, with an optimum growth temperature of 25–29°C (strain Bur 3) and 35–37°C (strain Bur 5) and at pH between 6.5 and 9.5, with an optimum pH value of 8.0–8.5. At pH 9.0, strain Bur 3 exhibits an increased content of phosphatidylglycerol and a decreased content of phosphatidylethanolamine. Strains Bur 3 and Bur 5 are similar in the G+C content of their DNAs (66.2 and 65.5 mol %, respectively) and in the type of the dominant ubiquinone (Q₁₀). Unlike Bur 5, strain Bur 3 is able to grow autotrophically in an atmosphere of CO₂+ O₂+ H₂. The strains oxidize, by the respective dehydrogenases, methanol to CO₂, which is assimilated by the ribulose bisphosphate pathway. Ammonium ions are assimilated in the glutamate cycle and by the reductive amination of -ketoglutarate. The strains are highly homologous to each other (92%) and are much less homologous (at a level of 28–35%) to representatives of the genus Ancylobacter, A. aquaticusATCC 25396^Tand A. vacuolatumDSM 1277. Based on the results obtained, both strains are assigned to a new species, Ancylobacter natronumsp. nov.