Feed-independence hydrolase production in T. reesei

The hydrolytic enzyme dosage required for efficient cellulose hydrolysis during the cellulose-to-ethanol ("Cellulosic Ethanol") process is very high and the cost of enzymes is a significant factor in overall biorefinery operating costs. Thus, the development of cost-effective hydrolytic enzymes is critical to the success of a commercial ethanol process. One of the approaches for reducing the enzyme production costs is the use of alternative low-cost carbon sources (e.g. lignocellulose hydrolysates comprising glucose, xylose, and arabinose). Currently, one of the major technological approaches requires addition of costly (hemi)cellulase-inducing carbohydrates into Trichoderma fermentation media. Further cost reduction could be realized if production of high- quality hydrolases can be achieved in the absence of (hemi)cellulase inducers and during fermentation on low-cost carbon sources (e.g. lignocellulose hydrolysates). The project focuses on genetic engineering of Trichoderma reesei to achieve these goals.

Cellulosic ethanol would be a good substitution for fossil fuels considering that it is derived from non-food, renewable biowaste. However, it is still not really a competitive product on the market, but relies on governmental subvention. In particular, the hydrolytic enzyme dosage required for efficient lignocellulose hydrolysis during the conversion to ethanol is very high and the cost of these enzymes is a significant factor in overall biorefinery operating costs. Thus, the development of cost-effective hydrolytic enzymes is critical to the success of a commercial biofuel/biorefinery process. Currently, the fungus Trichoderma reesei is used for industry-scale production of these enzymes. A sufficiently high enzyme production requires the addition of expensive inducing substances into the Trichoderma fermentation medium. The project FIND-HYPRO strived for the identification of measurements that enable high enzyme production without these costly inducers and instead of that to use cheap substrates such as lignocellulose hydrolysates (a mixture of glucose, D-xylose, L-arabinose, and others). Additionally to the low-cost enzyme production, the fungus T. reesei was tested for the production of a sweetener, called erythrit or erythritol. For this purpose, the genome of the fungus was modified and the obtained strains were simply grown on wheat straw. During this cultivation procedure the fungal strains synthesised the sweetener without any need of further expensive medium components. The process is promising from a socio-economical point: it does not need sugars as substrates, which are currenly used in very high concentrations for the production of this sweetener.