Hexachlorocyclohexane-degrading bacterial strains Sphingomonas paucimobilis B90A, UT26 and Sp+, having similar lin genes, represent three distinct species, Sphingobium indicum sp. nov., Sphingobium japonicum sp. nov. and Sphingobium francense sp. nov., and reclassification of [Sphingomonas] chungbukensis as Sphingobium chungbukense comb. nov.

Abstract

Three strains of Sphingomonas paucimobilis, B90A, UT26 and Sp+, isolated from different geographical locations, were found to degrade hexachlorocyclohexane. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these strains do not fall in a clade that includes the type strain, Sphingomonas paucimobilis ATCC 29837T, but form a coherent cluster with [Sphingomonas] chungbukensis IMSNU 11152T followed by Sphingobium chlorophenolicum ATCC 33790T. The three strains showed low DNA–DNA relatedness values with Sphingomonas paucimobilis ATCC 29837T (8–25 %), [Sphingomonas] chungbukensis IMSNU 11152T (10–17 %), Sphingobium chlorophenolicum ATCC 33790T (23–54 %) and Sphingomonas xenophaga DSM 6383T (10–28 %), indicating that they do not belong to any of these species. Although the three strains were found to be closely related to each other based on 16S rRNA gene sequence similarity (99·1–99·4 %), DNA–DNA relatedness (19–59 %) and pulsed-field gel electrophoresis (PFGE) patterns indicated that they possibly represent three novel species of the genus Sphingobium. The three strains could also be readily distinguished by biochemical tests. The three strains showed similar polar lipid profiles and contained sphingoglycolipids. The strains differed from each other in fatty acid composition but contained the predominant fatty acids characteristic of other Sphingobium species. A phylogenetic study based on 16S rRNA gene sequences showed that [Sphingomonas] chungbukensis IMSNU 11152T formed a cluster with members of the genus Sphingobium. Based on these results, it is proposed that strains B90A, UT26 and Sp+, previously known as Sphingomonas paucimobilis, are the type strains of Sphingobium indicum sp. nov. (=MTCC 6364T=CCM 7286T), Sphingobium japonicum sp. nov. (=MTCC 6362T=CCM 7287T) and Sphingobium francense sp. nov. (=MTCC 6363T=CCM 7288T), respectively. It is also proposed that [Sphingomonas] chungbukensis be transferred to Sphingobium chungbukense comb. nov.