Methylophaga muralis Bur 1, a haloalkaliphilic methylotroph isolated from the Khilganta soda lake (Southern Transbaikalia, Buryat Republic)

Abstract

A haloalkaliphilic restricted facultative methylotroph, strain Bur 1, which used methanol, methylated amines, and fructose as carbon and energy sources, was isolated from the soda Lake Khilganta (Buryat Republic, Russia). The cells were gram-negative non-spore-forming, motile rods reproducing by binary fission. The organism was aerobic, reduced nitrates to nitrites. Growth occurred at temperatures from 4 to 37°C (optimum at 25–29°C), pH 7.5–10.5 (optimum at 8.5–9.5), and NaCl concentration in the medium from 0.05 to 10.0% NaCl (optimum at 3–4%). Ectoine, glutamate, and sucrose were accumulated as osmoprotectants. Activity of the enzymes of de novo ectoine biosynthesis were detected. The organism utilized C1 compounds via the KDPG variant of the ribulose monophosphate pathway. The DNA G + C content was 44.67 mol %. Based on the similarity of the 16S rRNA gene sequences (94.7–99.1%) and the results of DNA–DNA hybridization (24–74%) with type strains of the neutrophilic and alkaliphilic Methylophaga species, the isolate was identified as Methylophaga muralis Bur 1 (VKM B-3046 = DSM 103617). The genome of M. muralis Bur 1 contained 2585 protein-encoding genes; 634 proteins with unidentified functions were predicted. Three rRNAs (5S, 16S, and 23S) and 38 tRNAs were identified. Apart from the mxaFJGIRSACKLDEH classical cluster of methanol oxidation genes, the xoxF gene was found. Methylamine was oxidized to formaldehyde by methylamine dehydrogenase and via the N-methylglutamate pathway. Orthologs of type III glutamine synthetases were revealed in the genome. The operons of ectoine and sucrose biosynthesis, ectRABC-ask and sps-spp-fruK-ams, were found. The genomes of M. muralis Bur 1 and M. lonarensis MPLT, unlike that of M. nitratireducenticrescens JAM1T, were found to contain the genes encoding the proteins of bicarbonate transport.