Taxonomic characterization of Ketogulonigenium vulgare gen. nov., sp nov and Ketogulonigenium robustum sp nov., which oxidize L-sorbose to 2-keto-L-gulonic acid

Four bacterial strains that oxidize L-sorbose to 2-keto-L-gulonic acid, a key intermediate in the synthesis of vitamin C, were isolated from soils of geographically distinct locations. All were Gram-negative, facultatively anaerobic, chemoheterotrophic rods. Comparative analysis revealed nearly identical 16S rDNA sequences amongst them (99.7-100% identical) and identified them as members of the alpha -subclass of the Proteobacteria. Phylogenetic analysis identified the closest taxonomically defined genus as Roseobacter (92.1-92.8 % identical). On the basis of phylogenetic, phenotypic and genotypic analyses, a new genus is proposed, Ketogulonigenium gen. nov. Based upon these analyses, we also propose the reclassification of strain DSM 4025(TP), originally identified as Gluconobacter oxydans, to the genus Ketogulonigenium. Two species are proposed: the type species Ketogulonigenium vulgare gen. nov., sp. nov., consisting of strains 62A-12A(PP), 266-13B(PP) and the type strain K, vulgare DSM 4025(TP), and Ketogulonigenium robustum gen. nov., sp. nov., consisting of the type strain K. robustum X6L(TP) (= NRRL B-21627 = KCTC 0858BP). The species affiliation of the fifth strain (291-19(PP)) remains unresolved.