Methylohalomonas lacus gen. nov., sp. nov. and Methylonatrum kenyense gen. nov., sp. nov., methylotrophic gammaproteobacteria from hypersaline lakes.

Aerobic enrichment at 4 M NaCl, pH 7.5, with methanol as carbon and energy source from sediments of hypersaline chloride–sulfate lakes in Kulunda Steppe (Altai, Russia) resulted in the isolation of a moderately halophilic and obligately methylotrophic bacterium, strain HMT 1T. The bacterium grew with methanol and methylamine within a pH range of 6.8–8.2 with an optimum at pH 7.5 and at NaCl concentrations of 0.5–4 M with an optimum at 2 M. In addition to methanol and methylamine, it can oxidize ethanol, formate, formaldehyde and dimethylamine. Carbon is assimilated via the serine pathway. The main compatible solute is glycine betaine. 16S rRNA gene sequence analysis placed the isolate as a new lineage in the family Ectothiorhodospiraceae (Gammaproteobacteria). It is proposed, therefore, to accommodate this bacterium within a novel genus and species, Methylohalomonas lacus gen. nov., sp. nov., with HMT 1T (=DSM 15733T =NCCB 100208T =UNIQEM U237T) as the type strain. Two strains were obtained in pure culture from sediments of soda lake Magadi in Kenya and the Kulunda Steppe (Russia) on a mineral medium at pH 10 containing 0.6 M total Na+ using methanol as a substrate. Strain AMT 1T was enriched with methanol, while strain AMT 3 originated from an enrichment culture with CO. The isolates are restricted facultative methylotrophs, capable of growth with methanol, formate and acetate as carbon and energy sources. With methanol, the strains grew within a broad salinity range from 0.3 to 3.5–4 M total Na+, with an optimum at 0.5–1 M. The pH range for growth was between 8.3 and 10.5, with an optimum at pH 9.5, which characterized the soda lake isolates as obligate haloalkaliphiles. Carbon is assimilated autotrophically via the Calvin–Benson cycle. Sequence analysis of the gene coding for the key enzyme RuBisCO demonstrated that strain AMT 1T possessed a single cbbL gene of the ‘green’ form I, clustering with members of the family Ectothiorhodospiraceae. Analysis of the 16S rRNA gene sequence showed that strains AMT 1T and AMT 3 belong to a single species that forms a separate lineage within the family Ectothiorhodospiraceae. On the basis of phenotypic and genetic data, the novel haloalkaliphilic methylotrophs are described as representing a novel genus and species, Methylonatrum kenyense gen. nov., sp. nov. (type strain AMT 1T =DSM 15732T =NCCB 100209T =UNIQEM U238T).