Optimization of physicochemical parameters for the enhancement of carbonyl reductase production by Candida viswanathii

Culture conditions have been optimized for a newly isolated yeast strain Candida viswanathii PBR2 which is capable of reducing a wide variety of aryl ketones with high stereospecificity. Studies on the culture conditions and catalytic performance of this microorganism showed that the carbonyl reductase occurs constitutively in the cells and its production is enhanced by feeding with acetophenone (2 mM) during the early period of cultivation. Mannitol (1%, wv⁻¹) was found to be beneficial both for growth and enzyme production. Supplementation of the media with yeast extract (1.0%, wv⁻¹) and Ca²⁺ (4 mM) enhanced the enzyme production. The optimal temperature and pH for the growth and enzyme production were 25 °C and 9.0, respectively. Excellent conversions along with almost absolute enantioselectivity were observed when the resting cells of this yeast strain were exploited to carry out the stereoselective reduction of a number of aryl ketones.