Biotransformation of d -Limonene to (+) trans -Carveol by Toluene-Grown Rhodococcus opacus PWD4 Cells

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Abstract
The toluene-degrading strain Rhodococcus opacus PWD4 was found to hydroxylate d -limonene exclusively in the 6-position, yielding enantiomerically pure (+) trans -carveol and traces of (+) carvone. This biotransformation was studied using cells cultivated in chemostat culture with toluene as a carbon and energy source. The maximal specific activity of (+) trans -carveol formation was 14.7 U (g of cells [dry weight]) −1 , and the final yield was 94 to 97%. Toluene was found to be a strong competitive inhibitor of the d -limonene conversion. Glucose-grown cells did not form any trans -carveol from d -limonene. These results suggest that one of the enzymes involved in toluene degradation is responsible for this allylic monohydroxylation. Another toluene degrader ( Rhodococcus globerulus PWD8) had a lower specific activity but was found to oxidize most of the formed trans -carveol to (+) carvone, allowing for the biocatalytic production of this flavor compound.