Influence of carbon and nitrogen sources and temperature on hyperproduction of a thermotolerant β-glucosidase from synthetic medium by Kluyveromyces marxianus

The effect of carbon source and its concentration, inoculum size, yeast extract concentration, nitrogen source, pH of the fermentation medium, and fermentation temperature on beta-glucosidase production by Kluyveromyces marxianus in shake-flask culture was investigated. These were the independent variables that directly regulated the specific growth and beta-glucosidase production rate. The highest product yield, specific product yield, and productivity of beta-glucosidase occurred in the medium (pH 5.5) inoculated with 10% (v/v) inoculum of the culture. Cellobiose (20 g/L) significantly improved beta-glucosidase production measured as product yield (Y-P/S) and volumetric productivity (Q(P)) followed by sucrose, lactose, and xylose. The highest levels of productivity (144 IU/[L(.)h]) of beta-glucosidase occurred on cellobiose in the presence of CSL at 35degreesC and are significantly higher than the values reported by other researchers on almost all other organisms. The thermodynamics and kinetics of beta-glucosidase production and its deactivation are also reported. The enzyme was substantially stable at 60degreesC and may find application in some industrial processes.