ENANTIOSELECTIVITY OF SULCATONE REDUCTION BY SOME ANAEROBIC-BACTERIA

Prominent among several factors that have been reported to affect the enantioselectivity of ketone reduction by washed suspensions of microo rganisms are (i) the phase of batch culture at which the organisms are harvested and (ii) the concentration at which the ketone is supplied. Sulcatone (6-methylhept-5-en-2-one) is only poorly soluble in aqueous media, but in the present study a novel microbe friendly organic solv ent mixture was employed to present this ketone in a range of concentr ations to cell suspensions of four bacteria that were then incubated i n an atmosphere of hydrogen for 6 h at 30 degrees C. The bacteria empl oyed were Clostridium pasteurianum, Clostridium tyrobutyricum (two str ains), and Lactobacillus brevis that had been harvested at various tim es from anaerobically growing batch cultures. L. brevis formed R(-)-su lcatol in high enantiomeric excess irrespective of its period of pregr owth in batch culture and the substrate sulcatone concentration (over the range 0.02-1.5 mM); however; in the case of all three clostridia, the enantiomeric selectivity of sulcatone reduction was substantially affected by both of these factors. It is likely that this reflects the possession by these clostridia of multiple ketone reductases differin g in their K-m values for sulcatone and present in the organisms in di ffering proportions during the course of their batch culture growth. ( C) 1997 Elsevier Science Inc.