Tabrizicola oligotrophica sp. nov. and Rhodobacter tardus sp. nov., two new species of bacteria belonging to the family Rhodobacteraceae

Two Gram-stain-negative, aerobic, non-motile bacteria, designated KMS-5^T and CYK-10^T, were isolated from freshwater environments. 16S rRNA gene sequence similarity results indicated that these two novel strains belong to the family Rhodobacteraceae. Strain KMS-5^T is closely related to species within the genus Tabrizicola (96.1-96.8 % sequence similarity) and Cypionkella (96.5-97.0 %). Strain CYK-10^T is closest to Rhodobacter thermarum YIM 73036^T with 96.6 % sequence similarity. Phylogenetic analyses based on 16S rRNA gene sequences and an up-to-date bacterial core gene set showed that strain KMS-5^T is affiliated with species in the genus Tabrizicola and strain CYK-10^T is placed in a distinct clade with Rhodobacter blasticus ATCC 33485^T, Rhodobacter thermarum YIM 73036^T and Rhodobacter flagellatus SYSU G03088^T. These two strains shared common chemotaxonomic features comprising Q-10 as the major quinone, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine as the principal polar lipids, and C_18 : 1  ω7c as the main fatty acid. The average nucleotide identity, average amino acid identity and digital DNA-DNA hybridization values between these two novel isolates and their closest relatives were below the cut-off values of 95-96, 90 and 70 %, respectively, used for species demarcation. The obtained polyphasic taxonomic data suggested that strain KMS-5^T represents a novel species within the genus Tabrizicola, for which the name Tabrizicola oligotrophica sp. nov. is proposed with KMS-5^T (=BCRC 81196^T=LMG 31337^T) as the type strain, and strain CYK-10^T should represent a novel species of the genus Rhodobacter, for which the name Rhodobacter tardus sp. nov. is proposed with CYK-10^T (=BCRC 81191^T=LMG 31336^T) as the type strain.