Description of Sphingobium fuliginis sp. nov., a phenanthrene-degrading bacterium from a fly ash dumping site, and reclassification of Sphingomonas cloacae as Sphingobium cloacae comb. nov.

A phenanthrene-degrading bacterium, strain TKP(T), was isolated from a fly ash dumping site of the thermal power plant in Panki, Kanpur, India, by an enrichment culture method using phenanthrene as the sole source of carbon and energy. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain belonged to the genus Sphingobium, as it showed highest sequence similarity to Sphingobium herbicidovorans DSM 11019(T) (97.3 %) and Sphingomonas cloacae JCM 10874(T) (96.5 %), compared with only 91-93 % similarity to members of other genera such as Sphingomonas sensu stricto, Novosphingobium, Sphingopyxis and Sphingosinicella. In DNA-DNA hybridization experiments with strains that were closely related phylogenetically and in terms of 16S rRNA gene sequences, i.e. Sphingobium herbicidovorans DSM 11019(T) and Sphingomonas cloacae JCM 10874(T), strain TKP(T) showed less than 70 % relatedness. Strain TKP(T) contained sphingoglycolipids SGL-1 and SGL-2 and 18 : 1omega7c as the predominant fatty acid, with 16 : 0 as a minor component and 14 : 0 2-OH as the major 2-hydroxy fatty acid. Thus, phylogenetic analysis, DNA-DNA hybridization, fatty acid and polar lipid profiles and differences in physiological and morphological features from the most closely related members of the Sphingobium group showed that strain TKP(T) represents a distinct species of Sphingobium. The name Sphingobium fuliginis sp. nov. is proposed, with the type strain TKP(T) (=MTCC 7295(T)=CCM 7327(T)). Sphingomonas cloacae JCM 10874(T) formed a coherent cluster with members of Sphingobium, did not reduce nitrate to nitrite and had a fatty acid profile similar to those of Sphingobium species; hence Sphingomonas cloacae should be transferred to the genus Sphingobium as Sphingobium cloacae comb. nov., with the type strain JCM 10874(T) (=DSM 14926(T)).