Comparative genome analyses reveal insights into the marine adaptation of a novel bacterium Pontimicrobium maritimus sp. nov., isolated from seawater

Abstract

A novel gliding, Gram-stain-negative, rod-shaped, strictly aerobic bacterium, designated SW4T, was isolated from seawater in the West Sea, Korea. Strain SW4T grew optimally at 30 °C, pH 7.5, and NaCl 2% on MA. Phylogenetic analysis based on the 16S rRNA gene placed strain SW4T in the genus Pontimicrobium within the family Flavobacteriaceae, with its closest relative being Pontimicrobium aquaticum KCTC 72003T (97.0% similarity). However, genome analysis revealed significant divergence, with average nucleotide identity (ANI) of 81.6% and digital DNA-DNA hybridization (dDDH) value of 24.4%, supporting its designation as a new species. The genome consists of a 3.44 Mb circular chromosome and a plasmid, with a G + C content of 32%. In addition to the physiological distinct characteristics, comparative genomic analysis identified unique genes associated with heavy metal transport, nitrogen and sulfur cycling, oxidative and osmotic stress responses, and numerous carbohydrate-active enzymes that are responsible for polysaccharide degradation and utilization, highlighting its marine adaptation. These findings differentiate strain SW4T from its closest and only existing species of P. aquaticum at both genomic and phenotypical levels. Based on phenotypic and phylogenetic evidence, we propose the novel species Pontimicrobium maritimus. sp. nov. with the type strain SW4T (= KCTC 42599T = InaCC B 1659T).