Sphingobium fluminis sp. nov. and Sphingobium anseongense sp. nov., isolated from riverbank soil

Two novel Gram-stain-negative, aerobic, heterotrophic, motile bacterial strains, designated AN558^T and AN641^T, were isolated from riverbank soil in South Korea. To determine their taxonomic positions, the strains were characterized using a polyphasic taxonomic approach based on 16S rRNA gene phylogeny, phenotypic and chemotaxonomic characteristics and genome-based analyses. Phylogenetic and genome-based analyses revealed that the two novel isolates, AN558^T and AN641^T, belong to the genus Sphingobium. AN558^T showed the highest 16S rRNA gene similarity (97.3%) with Sphingobium yanoikuyae ATCC 51230^T. In addition, AN641^T showed 97.6% 16S rRNA gene similarity with Sphingobium arseniciresistens H39-3-25^T. The genome of strains AN558^T and AN641^T consisted of 3,717,653 and 3,426,895 bp, with DNA G+C content of 62.8 and 63.6 mol%, respectively. The average nucleotide identity between the two strains and other related species was below 79.1%, and the digital DNA-DNA hybridization values with closely related species were below 22.4%, both lower than the species delineation threshold. Strains AN558^T and AN641^T contained ubiquinone Q-10 as the major respiratory quinone and exhibited a polyamine pattern, with spermidine as the predominant polyamine. The major fatty acids were characterized by C_16 : 0, C_16 : 1  ω7c/C1_6 : 1  ω6c (summed feature 3) and C_18 : 1  ω7c/C1_8 : 1  ω6c (summed feature 8). The major polar lipids of AN558^T and AN641^T were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid and phosphatidylcholine. Therefore, AN558^T and AN641^T represent novel species of the genus Sphingobium, for which the names Sphingobium fluminis sp. nov. (type strain AN558^T=KACC 23515^T=LMG 33415^T) and Sphingobium anseongense sp. nov. (type strain AN641^T=KACC 23516^T=LMG 33416^T) are proposed.