H2O2 feeding enables LPMO‐assisted cellulose saccharification during simultaneous fermentative production of lactic acid

• Published in: Biotechnology and bioengineering 2023-03, Vol.120 (3), p.726-736
• Main Authors: Hansen, Line D., Eijsink, Vincent G. H., Horn, Svein J., Várnai, Anikó
• Format: Article
• Language: English
• Subjects: Acid production; Anaerobic processes; Anoxic conditions; Bioreactors; biorefinery; Cellulase; Cellulose; Depolymerization; Fermentation; Hydrogen peroxide; Lactic acid; Lignocellulose; Low concentrations; LPMO; lytic polysaccharide monooxygenase; Optimization; Polysaccharides; Saccharification; simultaneous saccharification and fermentation
• ISSN: 0006-3592; 1097-0290
• DOI: 10.1002/bit.28298

Simultaneous saccharification and fermentation (SSF) is a well‐known strategy for valorization of lignocellulosic biomass. Because the fermentation process typically is anaerobic, oxidative enzymes found in modern commercial cellulase cocktails, such as lytic polysaccharide monooxygenases (LPMOs), may be inhibited, limiting the overall efficiency of the enzymatic saccharification. Recent discoveries, however, have shown that LPMOs are active under anoxic conditions if they are provided with H2O2 at low concentrations. In this study, we build on this concept and investigate the potential of using externally added H2O2 to sustain oxidative cellulose depolymerization by LPMOs during an SSF process for lactic acid production. The results of bioreactor experiments with 100 g/L cellulose clearly show that continuous addition of small amounts of H2O2 (at a rate of 80 µM/h) during SSF enables LPMO activity and improves lactic acid production. While further process optimization is needed, the present proof‐of‐concept results show that modern LPMO‐containing cellulase cocktails such as Cellic CTec2 can be used in SSF setups, without sacrificing the LPMO activity in these cocktails. Oxidative depolymerization of cellulose by lytic polysaccharide monooxygenases (LPMOs) accounts for one of the key mechanisms in enzymatic conversion of plant biomass to platform sugars. This proof‐of‐concept study shows that continuous feeding of H2O2 can unlock the cellulolytic potential of LPMOs in modern cellulase cocktails and thus improve the overall fermentation yield under the anoxic conditions of simultaneous saccharification and fermentation (SSF) setups.