Methylobacter arcticus sp. nov. isolated from a coal mine biofilm in the high Arctic Svalbard

An aerobic methanotroph was isolated from a biofilm of coal mine Gruve 7 (Svalbard) and designated strain G7^T. Cells of strain G7^T were Gram-stain-negative, pink-pigmented and motile rods. Strain G7^T could grow at pH 6.8 and at temperatures ranging from 4 to 21 °C. The genome size was 4.00 Mb with a (digital) DNA G+C content of 47.7 mol%. Strain G7^T represents a member of the family Methylomonadaceae of the class Gammaproteobacteria. It displayed 94.6-99.7% 16S rRNA gene sequence similarity to the type strains of the genus Methylobacter. Whole-genome comparisons based on average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) confirmed that strain G7^T represents a novel species. It showed 16S rRNA gene identity of 99.7%, 91.8% ANI and 46% dDDH to the closest type strain, Methylobacter svalbardensis LS7-T4A^T, with ANI and dDDH being much lower than the typically used 95 and 70% cutoffs, respectively, to delineate different species. For methane activation, strain G7^T carries genes encoding particulate methane monooxygenase (pmoCAB). Also, genes of the methane utilization pathways, i.e. oxidation of methane to carbon dioxide and assimilation of methane-carbon to biomass, were encoded in the genome. Strikingly, compared to all other Methylobacter spp. strains, strain G7^T did not have nitrogenase genes for nitrogen fixation. Strain G7^T also possessed genes for ectoine production, which was not observed in the genomes of its closest relatives. Based on phenotypic, genetic and phylogenetic data, strain G7^T represents a novel species within the genus Methylobacter for which the name Methylobacter arcticus sp. nov. is proposed, with strain G7^T (DSM: 117899; LMG: 33632) as the type strain.