Biotransformation of betulin to betulone by growing and resting cells of the actinobacterium Rhodococcus rhodochrous IEGM 66

•The ability of Rhodococcus actionobacteria to transform betulin to betulone was proved.•R. rhodochrous IEGM 66 exhibited the highest betulin-transforming ability.•Growing cells transformed betulin to betulone with 45% conversion rate within 240 h.•Resting cells catalyzed 40–60% betulone production within 24 h.

The ability of Rhodococcus actinobacteria to transform betulin to betulone was proved and reported for the first time. Betulone, the product of regioselective oxidation of a 3β-hydroxyl group of betulin, is a useful intermediate in the synthesis of novel biologically active compounds. Of 56 strains of Rhodococcus tested, Rhodococcus rhodochrous IEGM 66 was selected because it had the highest betulin-transforming ability. It was shown that R. rhodochrous IEGM 66 growing cells transformed 0.5 g/L betulin to betulone with 45% conversion rate within 240 h. A substantial reduction in the time of betulin (0.5 g/L) biotransformation was achieved by using resting cells, which catalyzed the production of 75% betulone after 96 h. At higher initial betulin concentrations (1.0–3.0 g/L), resting cells catalyzed 40–60% betulone production within 24 h.