Gluconobacter sphaericus has not yet been used in biotransformation studies. In this study, G. sphaericus SJF2-1, which produces a diffusible pigment, was isolated from grape. The spent culture medium became dark black when the cells were grown in medium containing glucose and then autoclaved. This bacterium produced 2,5-diketo-D-gluconate (2,5-DKG) from D-glucose and D-gluconate. When 5% D-glucose was used, the conversion efficiency was approximately 52.4% in a flask culture. 2,5-DKG is a precursor of 2-keto-L-gulonic acid, which is a key intermediate in the industrial production of L-ascorbic acid. The complete genome sequence of G. sphaericus SJF2-1 was determined for the first time in the G. sphaericus species. The total size was 3,198,086 bp, with 2867 protein-coding sequences; one chromosome and six plasmids were identified. From the genome of SJF2-1, multiple genes homologous to those involved in the conversion of D-glucose to 2,5-DKG were identified. In particular, six different genes encoding membrane-associated flavoprotein-cytochrome c complexed dehydrogenase were identified and divided into two different lineages. This study suggests the potential of G. sphaericus SJF2-1 to mass-produce 2,5-DKG and other D-glucose oxidation products.
Keywords: 2,5-diketo-D-gluconate; D-gluconate; D-glucose biotransformation; Gluconobacter sphaericus; L-ascorbic acid; membrane-associated flavoprotein-cytochrome c complexed dehydrogenase.