Chapter 11 - Production of Ethanol from Engineered Trichoderma reesei

Abstract

The nascent lignocellulosic ethanol industry relies on formulations of cellulases and hemicellulases, almost exclusively from the filamentous fungus, Trichoderma reesei, to generate monomeric sugars from the pretreated biomass. These sugars are then fermented to ethanol by various ethanologenic organisms. T. reesei not only has the ability to use the biomass sugars, d-glucose, d-mannose, d-galactose, d-xylose, and l-arabinose for growth, but also the basic biochemical pathway to ferment these sugars to ethanol, albeit at low rates and yields. We explored whether or not ethanol production from biomass sugars by T. reesei could be enhanced by engineering and enhancing the ethanol fermentative pathway beyond the wild type state. When genes coding for the two primary pathway enzymes for ethanol production, pyruvate decarboxylase (ScPDC1) and alcohol dehydrogenase (ScADH1), from the outstanding ethanologen, Saccharomyces cerevisiae, were expressed in T. reesei, the resulting strains showed significant increase in ethanol yield and a dramatic decrease of the byproduct, acetic acid, compared to the parent strain. These results demonstrate that T. reesei shows promise for being a useful organism for consolidated bioprocessing of biomass to ethanol with continued investment in pathway engineering.