Project Number: 3620-41000-147-00
Project Type: Appropriated

Start Date: Sep 01, 2009
End Date: Aug 31, 2014

Objective:
1) Determine the key metabolic, physiologic, transport, genetic, and regulatory mechanisms underlying stress tolerance and adaptation in ethanologenic yeast when they convert lignocellulosic hydrolyzates. 2) Via directed evolution, genetic engineering, and/or adaptation, create new commercially preferred yeast strains for converting lignocellulose hydrolyzates to ethanol. 3) In collaboration with Cooperative Research and Development (CRADA) partner(s), optimize fermentation process conditions so as to (1) leverage advantages of stress tolerant strains developed in Objective 2 and (2) minimize the cost of fermenting lignocellulosic hydrolyzates to fuel-grade ethanol.

Approach:
The lignocellulose-to-ethanol process involves pretreatment of biomass to predispose it to chemical and enzymatic hydrolysis, saccharification of sugar polymers to simple sugars, and fermentation of the sugars to ethanol. The hydrolysis product is difficult to ferment because inhibitory byproducts are produced, and the resulting sugar mixture contains both hexose and pentose sugars, the latter not fermentable by traditional brewing yeasts. Needed are improved yeast strains which will ferment both types of sugars and are able to withstand, survive, and function in the presence of inhibitors (including furfural and hydroxymethyl furfural), high ethanol concentration and osmotic pressure, and sufficiently elevated temperatures for simultaneous saccharification-fermentation processes. In the research proposed, fermentation hurdles will be overcome by combining process optimization strategies and strain improvements aided by new molecular biology tools allowing high throughput screening of whole genomes to identify key genes and gene networks involved in stress tolerance and sugar utilization. Products of the research will be stress-tolerant yeasts capable of resisting and detoxifying inhibitors and efficiently fermenting hexose and pentose sugars to ethanol, a genetic blueprint describing tolerance mechanisms and metabolic pathways, and optimal culture conditions and process configurations to lower costs by maximizing yeast stress resistance, ethanol productivity and yield.