Production of a highly glucose tolerant beta-glucosidase by Paecilomyces variotii MG3: optimization of fermentation conditions using Plackett-Burman and Box-Behnken experimental designs

Abstract

Beta-Glucosidases (beta-d-glucoside glucohydrolase, 3.2.1.21) are a group of enzymes mainly involved in the hydrolysis of beta-glycosidic bonds connecting carbohydrate residues in different classes of beta-d glycosides. During cellulose degradation they convert cellobiose and cellooligosaccharides produced by the endo and exoglucanases to glucose. Most of the microbial beta-glucosidases are inhibited by glucose. This limits their application in commercial scale cellulose degradation ventures. Solid state fermentation production of a highly glucose tolerant beta-glucosidase by a novel isolate of Paecilomyces was optimized using a two step statistical experiment design. In the first step which employed a Plackett-Burman design, the effects of parameters such as moisture, temperature, pH, inoculum concentration, incubation time and different concentrations of (NH(4))(2)SO(4), KH(2)PO(4), NaCl, peptone and cellobiose were evaluated. The parameters with significant influence on the process were selected and fine tuned in the second step using a Box-Behnken design. The model obtained was validated and a peptone concentration of 2 g/l, inoculum concentration of 1.2 x 10(6) spores/ml and an incubation period of 96 h were found to be optimum for the maximum production of the enzyme. The optimization resulted in a doubling of the enzyme production by the fungus.