Carotenoid-Producing sp. nov. and sp. nov., Isolated from Marine Algae, and Emended Description of the Genus Xu . 2020.

Two Gram-stain-negative, facultatively aerobic, non-motile, catalase- and oxidase-positive, rod-shaped bacteria, designated strains DGS2-2 (orange-pigmented) and DGS5-3 (yellow-pigmented), were isolated from marine red algae collected in Korea. Strain DGS2-2 grew at 20-40°C, pH 6.0-10.0, and in 1.0-6.0% (w/v) NaCl, while DGS5-3 grew at 15-40°C, pH 6.0-10.0, and in 2.0-6.0% NaCl. Ubiquinone-10 was the sole respiratory quinone. The G+C contents were 62.5% for DGS2-2 and 57.5% for DGS5-3. Both strains contained summed feature 8 (C7 and/or C6) and C as major fatty acids, and phosphatidylcholine, sphingoglycolipid, phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol as major polar lipids. The 16S rRNA gene similarity (97.3%), average nucleotide identity (ANI, 72.0%), and digital DNA-DNA hybridization (dDDH, 18.4%) values between the two strains were below the species delineation thresholds. Phylogenetic and phylogenomic analyses based on 16S rRNA gene and whole-genome sequences placed both strains in distinct lineages within the genus . ANI and dDDH values between each strain and type strains were below 74.5% and 19.5%, respectively, supporting their designation as novel species. Genomic analyses identified putative genes associated with potential algal symbiotic traits, including the biosynthesis of vitamins, siderophores, and hormone-like compounds. Carotenoid biosynthetic genes were also identified, and LC/MS confirmed astaxanthin (DGS2-2) and nostoxanthin (DGS5-3) production. Based on genomic, phylogenetic, phenotypic, and chemotaxonomic evidence, strains DGS2-2 and DGS5-3 represent two novel species of , for which the names sp. nov. (DGS2-2 =KACC 23855 =JCM 37496) and sp. nov. (DGS5-3 =KACC 23854 =JCM 37497) are proposed.