Pararhizobium antarcticum sp. nov., isolated from Antarctic water samples

Two bacterial strains were isolated from sediments and microbial mats of Kingfisher Pond, Antarctica and characterized in a taxonomic study using a polyphasic approach. Cells were strictly aerobic, Gram-stain-negative, rod-shaped, motile (+50 flagellum-specific genes present in the genome sequence; motility observed under microscope) and formed creamy white, half-transparent colonies. Growth occurred at 4 to 28 °C with an optimum at 20 °C, with 0-5.0 % (w/v) NaCl (optimum at 0-1.0 %) and at pH 4.0-11.0 (optimum pH 7.0-9.0). The major fatty acid was C18 : 1ω7c. The respiratory quinone was ubiquinone 10 (Q-10). The DNA G+C content was 60.7 mol %. The polar lipids were phosphatidylglycerol, phosphatidylethanolamine and phosphatidylmethanolamine in addition to three unidentified lipids, one unknown glycolipid and five unidentified phospholipids. Comparative analysis of 16S rRNA gene sequences showed highest sequence similarity (98.1 %) to Pararhizobium giardinii H152T, Pararhizobium herbae CCBAU 83011T, and 'Pararhizobium polonicum' F5.1. In silico average nucleotide identity (ANI) and genome-to-genome distance calculator (GGDC) showed 81.1 % identity (ANI) and 22.6 % identity (GGDC) to the closest relative, 'P. polonicum' F5.1. On the basis of phenotypic, phylogenetic, genomic and chemotaxonomic data, the two strains represent a novel species of the genus Pararhizobium, for which the name Pararhizobium antarcticum sp. nov. is proposed. The type strain is NAQVI 59T(=DSM 103442T=LMG 29675T).