Xanthobacter sp. C20 contains a novel bioconversion pathway for limonene

Xanthobacter sp. C20 was isolated from sediment of the river Rhine using cyclohexane as sole source of carbon and energy. Xanthobacter sp. C20 converted both enantiomers of limonene quantitatively into limonene-8,9-epoxide, a not previously described bioconversion product of limonene. With (4R)-limonene, (4R,8R)-limonene-8, 9-epoxide was formed as the only reaction product, while (4S)-limonene was converted into a (78:22) mixture of (4S,8R)- and (4S,8S)-limonene-8,9-epoxide. Cytochrome P-450 was shown to be induced concomitantly with limonene bioconversion activity following growth of Xanthobacter sp. C20 on cyclohexane. Maximal limonene bioconversion rate was observed at an initial substrate concentration of 12 mM. The amount of limonene-8,9-epoxide formed, up to 0.8 g l(-1), was limited by a strong product inhibition.