Discovering Functional Diversity of Lytic Polysaccharide Monooxygenases from the Thermophilic Fungus Myceliophthora Thermophila and Their Application in Lignocellulosic Biomass Degradation

Although lytic polysaccharide monooxygenase (LPMO) genes are highly abundant in the genomes of ascomycetes and basidiomycetes, their biological roles in single species for lignocellulose degradation remain unclear. Herein, transcriptomic analysis of the efficient biomass degrader Myceliophthora thermophila grown on corn straw revealed a high number and transcript abundance of LPMOs and glycoside hydrolases (GHs) in response to lignocellulose degradation. To gain a deeper understanding of the roles of LPMOs, phenotypic characterization of single gene deletion mutants and catalytic properties of recombinant LPMOs were valuated. Single gene deletion mutants of these highly expressed AA9 LPMOs exhibited no significant reduction in growth rate on corn straw compared to the wild-type strain. Functional characterization of these AA9 LPMOs showed significant differences in oxidative regioselectivity, catalytic activity, and substrate specificity. Notably, MtLPMO9G exhibited dual catalytic activities, degrading cellulose and xylan through oxidation and hydrolysis reactions, respectively. Moreover, synergistic actions between AA9 LPMOs and GHs from various families on enzymatic saccharification of corn straw with alkaline pretreatment showed that MtLPMO9G and MtLPMO9H increased the catalytic efficiency of cellulolytic GHs by 28 to 242%. These findings demonstrate great application potential of MtLPMO9G and MtLPMO9H in designing LPMO-containing cellulase cocktails for efficient enzymatic saccharification of lignocellulosic biomass.