Optimization of synergistic degradation of steam exploded corn straw by lytic polysaccharide monooxygenase R17L and cellulase

Hundreds of millions of tons of corn straw are available each year, and its main component is crystalline cellulose, which is currently underutilized by enzyme preparations, resulting in a waste of resources. The synergistic action of lytic polysaccharide monooxygenase (LPMO) and cellulase can significantly improve the conversion efficiency of cellulose, and then generate bioenergy or other valuable chemicals. In this study, corn straw was first pretreated with steam explosion at 200 °C for 3, 6, 9 and 12 min, and its chemical composition was analyzed. It was found that the hemicellulose content gradually decreased, and the cellulose content tended to increase as the pretreatment time increased. The results on the degradation of different pretreated corn straw showed that LPMO mutant R17L (Guo et al., 2020) and cellulase had the best synergistic effect on corn straw pretreated at 200 °C for 3 min. Comparing the results of degradation of corn straw at different pH, it was found that the reducing sugar produced by the degradation of corn straw at pH 6.0 were higher than that at pH 7.0. By analyzing the synergistic effect of different doses of R17L and cellulase, the optimal enzyme cocktail was 4 mg of R17L and 0.2 mL of commercial cellulase per gram of corn straw. Finally, by analyzing the surface morphology of corn straw under different enzymatic systems, it was found that the corn straw degraded by R17L in synergy with cellulase was the most fragmented, indicating that R17L disrupted the structure of corn straw, thus providing more operable sites for cellulase to achieve efficient conversion of biomass.