Screening of bacterial and fungal strains for cellulase and xylanase production using distillers' dried grains with solubles (DDGS) as the main feedstock

Bioenergy is one of the most promising solutions for the environmental problems of using non-renewable energy resources. Bioethanol is a form of bioenergy produced from food crops, such as corn, wheat, and sugarcane. Distillers' dried grains with solubles (DDGS) is the by-product of corn and wheat ethanol production in the dry mill process and has a high nutritional profile. The undigested carbohydrate components in DDGS and proteins can be utilized as the feedstock to produce microbial cellulases and xylanases as the value-added products. Currently, several bacterial and fungal strains are used to produce such enzymes by using expensive feedstocks for commercial preparations. In this study, several bacterial and fungal strains have been evaluated to explore the potential of hydrolyzed DDGS as the main feedstock for these hydrolytic enzymes production. Maximum cellulase production of 0.592 IU/ml was observed for Aspergillus niger (NRRL 1956) on the eighteenth day and stable high production of xylanase of 34.8 IU/ml was obtained for Aspergillus niger (NRRL 567) on day twelfth during shake-flask fermentation. Hydrolytic enzyme production by Bacillus subtilis (NRRL NSR352, DSM 17766, and NF1) was relatively lower (0-0.261 IU/ml for cellulase and 1.2-5.2 IU/ml for xylanase) than the fungal enzyme production. In conclusion, this study demonstrated that hydrolyzed DDGS can be an alternative economical substrate for A. niger strains to produce cellulase and xylanase, respectively. The next phases of the study should further optimize the production of cellulase and xylanase in terms of growth parameters and medium components by using bench-top bioreactors.