Flagellimonas ulvae sp. nov. and Flagellimonas rhodophyticola sp. nov., isolated from marine algae.

Two Gram-stain-negative, strictly aerobic, non-motile, rod-shaped bacteria, designated strains S174ᵀ and W118ᵀ, were isolated from the marine green alga Ulva prolifera and the marine red alga Schizymenia dubyi, respectively, collected in South Korea. Both strains exhibited catalase- and oxidase-positive activities and grew optimally at 25 °C, pH 8.0 and 2.0% (w/v) NaCl. The major fatty acids (>10%) in both strains were iso-C15:1 G, iso-C15:0 and iso-C17:0 3-OH, with phosphatidylethanolamine as the major polar lipid and menaquinone-6 as the predominant respiratory quinone. The genomic DNA G+C contents, based on whole-genome sequences, were 39.1 mol% for both strains. Strains S174ᵀ and W118ᵀ shared 93.6% 16S rRNA gene sequence similarity, 72.7% average nucleotide identity (ANI) and 17.5% digital DNA-DNA hybridization (dDDH), supporting their classification as distinct species. Phylogenetic analyses based on 16S rRNA gene and genome sequences placed both strains in distinct lineages within the genus Flagellimonas. Strains S174ᵀ and W118ᵀ were most closely related to Flagellimonas meridianipacifica SW027ᵀ (97.2%) and Flagellimonas onchidii XY-359ᵀ (97.9%), respectively, and ANI and dDDH values with other type strains were below 84.6 and 28.2%, respectively, confirming their novelty. Based on phenotypic, chemotaxonomic and genomic features, strains S174ᵀ and W118ᵀ represent two novel species of the genus Flagellimonas, for which the names Flagellimonas ulvae sp. nov. (S174ᵀ=KACC 24029ᵀ=JCM 37803ᵀ) and Flagellimonas rhodophyticola sp. nov. (W118ᵀ=KACC 24030ᵀ=JCM 37802ᵀ) are proposed.