An integrated in silico and in vitro approach to optimize Aspergillus niger xylanase using agricultural wastes for bioethanol production

Fungi and agricultural waste have drawn more attention as a source of xylanase enzyme synthesis recently. In this study, fungal isolates able to produce xylanase were isolated from the soil sample. Within the 19 isolates, three exhibited the highest activity as determined by the Dinitro Salicylic Acid (DNS) method. These isolates were cultivated using various agricultural wastes as cheap carbon sources (xylan), including corn cob, maize straw, sugar cane bagasse, wheat straw, wheat bran, rice husk, and sawdust. Out of the three isolates, the most effective one (WA7) and three agricultural wastes (rice husk 167 U mL −1 , corn cob 159 U mL −1 , wheat bran 154 U mL −1 ) were chosen based on the highest xylanase activity. Using Design-Expert, the optimization of xylanase production occurred in two phases. The first step was screening the essential fermentation parameters affecting xylanase production using the Plackett–Burman design. For the second step in optimization using a definitive screening design, the most important factors for enzyme synthesis from the fungal isolate were further investigated. The maximum xylanase yield after optimization was 242 U mL −1 . Based on genotypic characterization, the fungal isolate was identified as Aspergillus niger 28S ribosomal rRNA. Xylanase enzyme was used in four different processes to produce ethanol on various substrates. The fourth simultaneous saccharification and fermentation technique, which used rice husk as an environmentally friendly waste, was shown to be the most effective, with ethanol yields reaching 40 g L −1 . Further, A. niger xylanase showed optimal molecular interaction and binding affinity toward xylan: −8.00 kcal/mol. Based on these results, A. niger xylanase showed a promising perspective for xylan hydrolysis to produce ethanol.