Light Exposure of Lignin Affects the Saccharification Efficiency of LPMO-Containing Cellulolytic Enzyme Cocktails

Efficient enzymatic saccharification of lignocellulosic substrates requires a blend of different hydrolytic and oxidative enzymes: cellulases, β-glucosidases, and lytic polysaccharide monooxygenases (LPMOs). In aerobic systems, reactions between lignin and oxygen will generate the LPMO cosubstrate H2O2. This in situ generation of H2O2 is essential to keep LPMOs active during saccharification processes but is challenging to control, particularly in the presence of transition metals. In this study, H2O2 generation and LPMO activity during saccharification reactions with LPMO-containing cellulolytic enzyme cocktails were manipulated using light of different wavelengths and lignin at different concentrations. The results show that light and its wavelength greatly impact H2O2 production resulting from abiotic oxidation of lignin, with major effects on LPMO activity, the stability of both the LPMOs and the cellulases, and saccharification efficiency. Light may have a negative effect on the overall efficiency of cellulolytic enzyme cocktails acting on lignin-containing cellulosic material, because light can induce excessive production of H2O2. Importantly, our data suggest that the LPMOs contribute not only by cleaving cellulose but also by removing excess H2O2 that otherwise could harm the cellulases.