12-09: Integration of lignocellulosic biomass hydrolyzates for enhanced on-site cellulase production by Trichoderma reesei

Cellulase supply and cost are key-issues for lignocellulosic biomass (LCB) bioconversion processes. Trichoderma reesei is the most studied and common industrial cellulase producer, and on-site cellulase production using process carbon sources has been evaluated as a cost-effective option. However, production of cellulases by batch fermentation using raw or pretreated cellulosic materials is difficult to handle, and gives much lower productivity and yield than fed-batch fermentation using soluble sugars feeding. LCB hydrolyzates are available soluble carbon sources but their use can be hampered by the presence of many different monomer sugars and degradation compounds.

A comprehensive study was carried out to assess the influence of the main components of LCB hydrolyzates on growth and cellulase production by Trichoderma reesei. First, many degradation compounds (weak organic acids, furanic and  phenolic derivatives) were screened for their inhibition effect on Trichoderma reesei growth. Four strong inhibitors were identified and then, their effects on growth and cellulase production phase were quantified. Different mechanisms were observed: growth rate decrease, lag period, detoxification.

Concurrently, the influence of concentrations of hexose and pentose sugars on cellulase productivity and enzymatic activity was measured and modeled. Among the main results obtained, it was shown that i) cellulase productivity can be maintained at a very high level even when replacing 92% of inducer with non-inducing sugars, and ii) the integration of xylose had the strongest effect on all studied enzymatic activities.

These results have contributed to design an optimized process for enhanced on-site cellulase production.