Isolation and characterization of Novosphingobium aquae sp. nov. and Novosphingobium anseongense sp. nov., isolated from freshwater

Two novel Gram-stain-negative, aerobic, heterotrophic, non-motile bacterial strains, designated as AS3R-12^T and PS1R-30^T, were isolated from freshwater in South Korea. To determine their taxonomic positions, the strains were thoroughly characterized. Genomic analyses, based on 16S rRNA gene and draft genome sequence data, revealed that the two novel isolates, AS3R-12^T and PS1R-30^T, belonged to the genus <i>Novosphingobium</i>. AS3R-12^T showed the highest 16S rRNA gene similarity (97.7%) with <i>Novosphingobium flavum</i> UCT-28^T. In addition, PS1R-30^T showed 97.9% 16S rRNA gene similarity with <i>Novosphingobium lentum</i> NBRC 107847^T. The draft genome of strains AS3R-12^T and PS1R-30^T consisted of 4 149 275 and 4 969 838 bps, with DNA G+C content of 63.1 and 66.1 mol%, respectively. The average nucleotide identity between two strains and other related species was below 76.2%, and the digital DNA-DNA hybridization values with closely related species were below 20.8%, both lower than the species delineation threshold. Strains AS3R-12^T and PS1R-30^T contained the ubiquinone Q-10 as the major quinone and displayed a polyamine pattern with spermidine as the predominant polyamine. Additionally, their major fatty acids were characterized by C_16:1 <i> ω7c</i>/C_16:1 <i> ω6c</i> (summed feature 3) and C_18:1 <i> ω7c</i>/C_18:1 <i> ω6c</i> (summed feature 8). The major polar lipids of AS3R-12^T and PS1R-30^T were diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), sphingoglycolipid (SGL) and phosphatidylcholine (PC). Moreover, physiological and biochemical results allowed the phenotypic and genotypic differentiation of strains AS3R-12^T and PS1R-30^T from their closest and other species of the genus <i>Novosphingobium</i> with validly published names. Therefore, AS3R-12^T and PS1R-30^T represented novel species of the genus <i>Novosphingobium</i>, for which the names <i>Novosphingobium aquae</i> sp. nov. (type strain AS3R-12^T=KACC 23096^T=LMG 32950^T) and <i>Novosphingobium anseongense</i> sp. nov. (type strain PS1R-30^T=KACC 23097^T=LMG 32951^T) are proposed.