Octadecabacter algicola sp. nov. and Octadecabacter dasysiphoniae sp. nov., isolated from a marine red alga and emended description of the genus Octadecabacter.

Two Gram-stain-negative, strictly aerobic, catalase- and oxidase-positive and non-motile rod-shaped bacteria, strains D2-3T and G9-8T, were isolated from a marine red alga. Both strains contained ubiquinone-10 as the sole isoprenoid quinone. As the major cellular fatty acids (>5.0 %), D2-3T contained C16 : 0, 11-methyl-C18 : 1ω7c, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), and summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c), whereas G9-8T contained C16 : 0, 11-methyl-C18 : 1ω7c, C12 : 1 3-OH, and summed feature 8. The DNA G+C contents of D2-3T and G9-8T were 54.4 % and 56.0 %, respectively. As the major polar lipids, phosphatidylglycerol, diphosphatidylglycerol and unidentified phospholipid, aminolipid and lipid were identified from both strains, and phosphatidylcholine was additionally detected from G9-8T only. The 16S rRNA gene sequence similarity of D2-3T and G9-8T was 98.5 % and their digital DNA-DNA hybridization (DDH) value was 19.1 %. Phylogenetic analyses based on 16S rRNA gene and genome sequences revealed that D2-3T and G9-8T formed respectively distinct phylogenetic lineages within the genus Octadecabacter. D2-3T and G9-8T were most closely related to Octadecabacter ascidiaceicola RA1-3T and Octadecabacter antarcticus 307T, with 98.9 % and 98.5 % 16S rRNA gene sequence similarities, respectively, and digital DDH values between D2-3T and O. ascidiaceicola and between G9-8T and O. antarcticus were 18.3 % and 19.5 %, respectively. Phenotypic, chemotaxonomic and molecular features support the hypothesis that D2-3T and G9-8T represent two novel species of the genus Octadecabacter, for which the names Octadecabacter algicola sp. nov. and Octadecabacter dasysiphoniae sp. nov. are proposed. The type strains of O. algicola and O. dasysiphoniae are D2-3T (=KACC 22493T =JCM 34969T) and G9-8T (=KACC 22488T =JCM 34973T), respectively.