Tritonibacter aquimaris sp. nov. and Tritonibacter litoralis sp. nov., two novel members of the Roseobacter group isolated from coastal seawater

Two Gram-stain-negative bacterial strains, SM1969 T and SM1979 T , were isolated from coastal surface seawater of Qingdao, China. They were taxonomically characterized by the phylogenetic, genomic, chemotaxonomic and phenotypic analyses. The two strains shared 97.0% 16S rRNA gene sequence similarity with each other and the highest similarity (96.8–97.5%) with type strains of six species in the genera Shimia , Tritonibacter and Tropicibacter in the Roseobacter group of the family Rhodobacteraceae . In the phylogenetic tree based on single-copy orthologous clusters (OCs), both strains clustered with known species of the genus Tritonibacter and together formed a separate branch adjacent to Tritonibacter ulvae . Although sharing many chemotaxonomic and phenotypic characteristics, the two strains could be differentiated from each other and closely related species by numerous traits. Particularly, strain SM1969 T was found to have a DMSP lyase coding gene dddW in its genome and have the ability to produce DMS from DMSP while strain SM1979 T was not. The average nucleotide identity and in silico DNA-DNA hybridization values between strains SM1969 T and SM1979 T and type strains of closely related species were all below the thresholds to discriminate bacterial species, demonstrating that they constitute two new species in the genus Tritonibacter . The names Tritonibacter aquimaris sp. nov. and Tritonibacter litoralis sp. nov. are proposed for the two new species, with type strains being SM1969 T (= MCCC 1K04320 T = KCTC 72843 T ) and SM1979 T (= MCCC 1K04321 T = KCTC 72842 T ), respectively.