Azospirillum palustre sp. nov., a methylotrophic nitrogen-fixing species isolated from raised bog

Nitrogen-fixing bacterial strain, designated B2 T , was isolated from methane-oxidation enrichment originating from a Sphagnum -dominated raised peatland in Tver region, Russia, and its phenotypic, chemotaxonomic and genomic characteristics were investigated. Cells of isolate were Gram-negative, aerobic, rod or spiral-shaped, with motility provided by a single polar flagellum in liquid media and peritrichous flagella on solid media. Strain was able to grow at 15-40 °C, pH 5.5-8.5 and tolerated NaCl to 2.0 % (w/v). Strain B2 T gave positive amplification for dinitrogen reductase ( nifH gene) and acetylene reduction activity was recorded up to 1250 nmol ethylene h -1 (mg protein) -1 . Analysis of 16S rRNA showed that B2 T represents a member of the genus Azospirillum and had the highest sequence similarity with A. humicireducens SgZ-5 T (97.92 %). The predominant quinone system was ubiquinone Q-10 and the major fatty acids were C 18 : 1 ω7, C 16 : 1 ω7 and C 16 : 0 . The strain was facultative methylotrophic and used methanol and formate for the growth. Genome sequencing revealed a genome size of 8.0 Mbp and a G+C content of 67.8 mol%. The mx aFI genes encoding methanol dehydrogenase were absent, but a homologous xox F gene was detected. The genes encoding enzymes involved in the biosynthesis of tetrahydromethanopterin (H 4 MPT) (formaldehyde oxidation) and NAD-linked formate dehydrogenase ( fdsABG ) were identified. Pairwise determined whole genome average nucleotide identity (gANI) values confirmed that strain B2 T represents a novel species, for which we propose the name Azospirillum palustre sp. nov. with the type strain B2 T (VKM B-3233 T , КСТС 62613 Т ).