Spirosoma knui sp. nov., a radiation-resistant bacterium isolated from the Han River

A Gram-stain-negative, non-motile, non-spore-forming, rod-shaped, aerobic bacterium, designated 15J8-12^T, was isolated from a water sample after exposure to 3 kGy of gamma radiation. The strain showed resistance to gamma radiation with a dose required to reduce the bacterial population 10 fold (D₁₀) value of 4.7 kGy. The results of comparative 16S rRNA gene sequence analysis indicated that strain 15J8-12^T represented a member of the family Cytophagaceae, phylum Bacteroidetes, and was most closely related to ‘Spirosoma fluminis’ 15J17 (97.92%) and Spirosoma arcticum R2-35^T (92.22%). The G+C content of the genomic DNA of 15J8-12^T was 51.3 mol%. The detection of menaquinone MK-7 as the predominant respiratory quinone, a fatty acid profile with summed feature 3 (C_{16: 1}ω7c/C_{16: 1}ω6c; 40.5%), C_{16: 1}ω5c (35.3%), C_{15: 0} iso (6.9%) and C_{16: 0} (6.8%) as the major components and phosphatidylethanolamine as the major polar lipid also supported the affiliation of 15J8-12^T with the genus Spirosoma. The DNA–DNA relatedness between 15J8-12^T and ‘Spirosoma fluminis’ 15J17 was 27.8%. On the basis of its phenotypic and genotypic properties, together with its phylogenetic distinctiveness, 15J8-12^T should be considered to be a representative of a novel species of the genus Spirosoma, for which the name Spirosoma knui sp. nov. is proposed. The type strain is 15J8-12^T (=KCTC 52510^T=JCM 31407^T).