Optimisation of a dedicated cellulolytic enzymatic cocktail using on site available raw materials

Most processes for the biological conversion of ligno-cellulosic biomass (LCB) to bio-products require the use of cellulases. One of the most efficient organisms for the production of these enzymes is the imperfect fungus Trichoderma reesei, mainly thanks to its high secretion capacity. The produced enzymatic cocktail contains three important enzymes: endoglucanases (EG), cellobiohydrolases (CBH) and β -glucosidase (BGL1). The latter one is very poorly secreted by Trichoderma reesei strains and a complete hydrolysis of cellulose often requires supplementation with extra β-glucosidase, especially to prevent inhibition of CBHs by cellobiose.

The produced cocktail used was firstly optimised by cloning a more efficient β -glucosidase into T. reesei CL847 strain which is an industrial cellulase production strain.  Then we determined the kinetics of growth and enzyme production of this new strain using various hemicellulosic and cellulosic hydrolysates (wheat straw, etc). We observed that the substrate sugars composition strongly governed the composition of the enzymatic cocktail secreted by T. reesei in industrial fed-batch mode. The results obtained were used to develop a model predicting the effect of the substrate composition on the produced enzymatic activities.

These results illustrate how the economic success of using LCB as an industrial fermentation substrate in industry will largely be dependent on microbial capabilities and process considerations.