Methylomarinum roseum sp. nov., a Novel Halophilic Methanotrophic Bacterium from the Hypersaline Lake Elton

The genus Methylomarinum accommodates aerobic motile non-pigmented methanotrophic bacteria, which were isolated from marine habitats and require NaCl for growth. Until recently, this genus contained a single species, M. vadi . Here, we describe a novel Methylomarinum representative, strain Ch1-1 T , obtained from the sediments of the River Chernavka at its confluence with the hypersaline Lake Elton, Russia. Strain Ch1-1 T was represented by gram-negative, pink-pigmented, motile rods or ovoids, which multiplied by binary fission and possessed the particulate methane monooxygenase (pMMO). These bacteria grew on methane within the temperature range of 5–42°C (optimum at 30–35°C) and at рH 6.3–7.5 (optimum at 6.5–6.8). Growth on methanol was inconsistent. NaCl was required for growth, which was observed in liquid media only within a NaCl concentration range of 0.5–10% (w/v). Best growth was recorded at a NaCl concentration of 3.5–4.0% (w/v). The 16S rRNA gene sequence of strain Ch1-1 T displayed 97.09–97.24% similarity to the corresponding gene fragments of described representatives of M. vadi . The genome of strain Ch1-1 T was 4.8 Mb in size and contained 3 rRNA operons and about 4400 protein-coding genes, including the gene cluster pmoCAB coding for pMMO, a complete set of genes for the function of the ribulose monophosphate pathway as well as genes necessary for ectoine and sucrose biosynthesis. The DNA G+C content was 50.7 mol %. The average nucleotide identity determined for genomes of strain Ch1-1 T and M. vadi IT-4 T was 78.8%. Based on the number of genotypic and phenotypic differences, we propose to classify this isolate as representing a novel species of the genus Methylomarinum, M. roseum sp. nov. strain Ch1-1 T (=VKM B-3852 T = UQM 41855 T ) is the type strain of the newly proposed species.