Applied Biochemistry and Biotechnology, Vol.172, No.7, 3606-3620, 2014
Exploration of a Cheaper Carbon Source for Extracellular beta-glucosidase Synthesis from Debaryomyces pseudopolymorphus NRRL YB-4229
In the present work, interactions between common media components and fermentation conditions were explored to come up with a simple media recipe for extracellular beta-glucosidase (D beta-gl) synthesis from Debaryomyces pseudopolymorphus to substitute cellobiose, which is currently used as a sole carbon source. Taguchi L-25 orthogonal array design was used to screen factors influencing D beta-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 D beta-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 D beta-gl synthesis. Peptone/xylose ratio of 1.33 was found to be an important parameter for inducing D beta-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 D beta-gl yield. Fed-batch fermentations were carried out wherein peptone/xylose ratio of 1.33 was maintained and continuous D beta-gl synthesis was observed.
Keywords:Debaryomyces pseudopolymorphus;Extracellular beta-glucosidase synthesis;Submerged fermentation;Xylose;Response surface methodology