Silicimonas algicola gen. nov., sp. nov., a member of the Roseobacter clade isolated from the cell surface of the marine diatom Thalassiosira delicatula

A Gram-negative, aerobic, non-motile bacterium, designated strain KC90BT, was isolated from the surface of a cell of the marine diatom Thalassiosira delicatula. The bacterial cells were pleomorphic and formed very small, beige colonies on marine agar. Optimal growth was obtained at 25 °C, at pH 6.5–7.5 and in the presence of 1.5–2.0 % (w/v) NaCl. Phylogenetic analyses based on its 16S rRNA gene sequence revealed that strain KC90BT belonged to the Roseobacter clade and formed a monophyletic cluster with the sequences of Boseongicola aestuarii , Profundibacterium mesophilum , Hwanghaeicola aestuarii , Maribius pelagius and M. salinus, showing 91.4–95.7 % sequence similarities. Ubiquinone Q-10 was the predominant lipoquinone but a significant amount of ubiquinone Q-9 was also detected. The major cellular fatty acids were C18 : 1 ω7c, 11-methyl C18 : 1 ω7c and C18 : 0. Strain KC90BT also contained specific fatty acids (C17 : 0, anteiso-C15 : 0 and anteiso-C17 : 0) that were not detected in its closest described relatives. The major polar lipids of strain KC90BT comprised phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol and an unidentified aminolipid. The DNA G+C content of strain KC90BT was 65.2 mol%. The phylogenetic analysis of strain KC90BT, together with the differential phenotypic and chemotaxonomic properties demonstrate that strain KC90BT is distinct from type strains of B. aestuarii , P. mesophilum , H. aestuarii , M. pelagius and M. salinus . Based on the data presented in this study, strain KC90BT represents a novel genus and species within the family Rhodobacteraceae , for which the name Silicimonas algicola gen. nov., sp. nov. is proposed. The type strain is KC90BT (=DSM 103371T=RCC 4681T).