A thermotolerant yeast strain, Kluyveromyces marxianus IMB3, has previously been shown to be capable of ethanol production following growth on lactose-containing media at 45°C. Here, we demonstrate that the organism is capable of producing inducible P-galactosidase activity in the presence of lactose. The majority of the activiw appears to be cell associated. Enzyme, isolated following disruption of the cells, has been partially characterized and shown to have a K,,, of 5 mM for the substrate o-nitrophenyl-P-o-galactoside, whereas thatfor lactose was found to be 40 mM. The activity was shown to have an optimal operating temperature of 50°C. although the half-life of the enzyme was shown to be <5 min at that temperature. The half-life of the isolated enzyme at 4S”C, the optimal fermenting temperature of the yeast, was shown to be 15 min. The enzyme was stable at 30°C for at least 8 h. The optimum pH was 7.5. When we analyzed the result using nondenaturing polyactyl- amide gradient gel electrophoresis together with zymogram staining with methylumbelltferyl-P-o-galactoside as substrate, two distinct forms of activity were observedfollowing prolonged incubation with substrate. The results suggest that although this yeast is capable of ethanol production at 4S”C, thermotolerance is not reflected in the enzyme activity associated with assimilation of lactose.
Keywords: Kluyveromyces marxianus; thermotolerant; ethanol; lactose; P-galactosidase
Introduction
For some time, lactose in whey has been recognized as an ideal substrate for the production of both fuel and potable ethanol via fermentation. ’ Efficient conversion and process design have been hindered by the facts that the concentra- tion of lactose in whey is relatively low and that relatively few fermenting yeasts are capable of lactose utilization. The most common alternatives to using conventional strains of Saccharomyces cerevisiae together with exogenously added
Address reprint requests to Dr. McHale, Biotechnology Group, School of Applied Biological and Chemical Sciences, University of Ulster, Cole- raine, BT52 ISA, Co. Londonderry, Northern Ireland Received 29 July 1994; revised 8 November 1994; accepted November 18, 1994
enzymes include strains
การแปล กรุณารอสักครู่..