Is LPMO activity affected by water availability during high dry matter enzymatic degradation of lignocellulose?

The use of lignocellulosic biomass for production of chemicals and fuels is now running at industrial scale. The performances of the newest cellulolytic enzyme cocktails when applied at industrial conditions, i.e. high dry matter (HDM), is therefore of large interest. HDM in biofuels production is defined as any process above 15% DM content.  Despite being advantageous for a final high product recovery, at the same time it also impairs the performance of the hydrolytic enzymes. Generally decreasing enzyme performance is observed at higher DM for the traditional cellulases, but so far no knowledge is available on how the activity of lytic polysaccharides monooxygenases (LPMO) are affected by HDM conditions.

The results shown that HDM conditions favor LPMO’s activity relative to the hydrolytic enzymes. While the latter were severely inhibited already at 10% DM, LPMOs were still equally functioning even at 30% DM. Increasing the level of cellulose oxidation by LPMOs lead to a higher water constraint presumably on the cellulose surface. Thus the role of HDM conditions on the activity of hydrolytic and/or oxidative enzymes was tested. We have found that high level of cellulose surface oxidations were inhibitory for hydrolytic enzymes, presumably for a water constraint effect or preventing their adsorption. LPMO activity instead did not suffer from any water constraint effect. Incubating LPMO with up to 150 g/l of solutes i.e. glucose, did not have any effect on the oxidizing activity towards cellulose. In conclusion LPMO is an enzyme suitable for high dry matter biotechnological processes.