ABSTRACT
In the present work, interactions between common media components and fermentation conditions were explored to come up with a simple media recipe for extracellular ß-glucosidase (Dß-gl) synthesis from Debaryomyces pseudopolymorphus to substitute cellobiose, which is currently used as a sole carbon source. Taguchi L25 orthogonal array design was used to screen factors influencing Dß-gl synthesis (carbon, organic nitrogen, inorganic nitrogen, trace elements, inoculum volume, and fermentation time). A significant influence of xylose, peptone, and potassium nitrate as carbon, organic nitrogen, and inorganic nitrogen sources, respectively, on Dß-gl synthesis was identified by Taguchi. These factors were further optimized using central composite rotatable design (CCRD) of response surface methodology (RSM). The results showed that in the range studied, potassium nitrate had insignificant effect while xylose, peptone, and xylose-peptone interaction had a significant effect on Dß-gl synthesis. Peptone/xylose ratio of 1.33 was found to be an important parameter for inducing Dß-gl synthesis. The regression coefficient (R (2)) of 0.915 and P value of <0.0003 for the model indicated that it was highly significant. The maximum activity obtained after RSM (32.2 U/ml) was comparable with that obtained (68.8 U/ml) when cellobiose (20 g/l) was used as a sole carbon source. Considering the cost difference between xylose and cellobiose, a 16-fold cost reduction could be obtained for equivalent Dß-gl yield. Fed-batch fermentations were carried out wherein peptone/xylose ratio of 1.33 was maintained and continuous Dß-gl synthesis was observed.