Two Gram-stain-negative, catalase- and oxidase-positive, and aerobic bacteria, strains MSW7T and MSW13T, were isolated from seawater. Cells of strains MSW7T and MSW13T are motile and non-motile rods, respectively. Strain MSW7T optimally grew at 25 °C and pH 7.0 and in the presence of 3 % (w/v) NaCl, whereas strain MSW13T optimally grew at 25 °C and pH 6.0-7.0 and in the presence of 2 % NaCl. As the sole respiratory quinone and the major fatty acids and polar lipids, strain MSW7T contained ubiquinone-8, C16 : 0, C15 : 1 ω8c, C17 : 1 ω8c and summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), and phosphatidylethanolamine and phosphatidylglycerol, respectively, whereas strain MSW13T contained menaquinone-6, C15 : 1 ω6c, iso-C15 : 0, anteiso-C15 : 0, and iso-C15 : 0 3-OH, and phosphatidylethanolamine, respectively. The DNA G+C contents of strains MSW7T and MSW13T were 37.3 and 29.9 %, respectively. Phylogenetic analyses based on 16S rRNA gene sequences showed that strains MSW7T and MSW13T were most closely related to Colwellia echini A3T and Polaribacter atrinae WP25T with 98.8 and 98.1 % sequence similarities, respectively. The average nucleotide identity and digital DNA-DNA hybridization values between strain MSW7T and C. echini A3T and between strain MSW13T and P. atrinae KACC 17473T were 73.6 and 22.6 % and 80.4 and 23.8 %, respectively. Based on phenotypic, chemotaxonomic and phylogenetic data, strains MSW7T and MSW13T represent novel species of the genera Colwellia and Polaribacter, respectively, for which the names Colwellia maritima sp. nov. and Polaribacter marinus sp. nov. are proposed, respectively. The type strains of C. maritima sp. nov. and P. marinus sp. nov. are MSW7T (=KACC 22339T=JCM 35001T) and MSW13T (=KACC 22341T=JCM 35021T), respectively.
Keywords: Bacteroidota; Colwellia maritima; Polaribacter marinus; Pseudomonadota; new taxa; seawater.