On hydrolysis, lignocellulosic substrates yield a mixture of monomeric hexoses (glucose, mannose and galactose) and pentoses (xylose and arabinose). To improve the economics of any biomass conversion process, it is imperative that potential biocatalysts be able to efficiently convert both the hexoses and pentoses in lignocellulosic hydrolysates into the desired endproduct(s). While many microorganisms can convert glucose efficiently into ethanol and other high value chemicals, the bioconversion of pen-toses remains inefficient. Moreover, carbon metabolism in most fermentative microorganisms is subject to glucose repression. Thus, in the presence of preferred sugars (mannose and glucose), less preferred sugars (xylose, arabinose and galactose) are poorly utilized and converted. Accordingly, research must be directed at:
- improving pentose metabolism in potential bioconversion microorganisms;
- improving simultaneous utilization of all the biomass sugars for bioconversion to the target com-pound(s); and
- designing microorganisms able to tolerate the inhibitors found in lignocellulosic hydrolysates; and 4) consolidating the enzyme hydrolysis and fermentation steps to reduce process costs.
Overall Aims: The overall aim of this Theme is to engineer yeast strains that will meet the needs of a cellulosic ethanol process. To achieve this, it is imperative that potential bioconversion microorganisms must be able to efficiently convert all the hexoses and pentoses in lignocellulosic hydrolysates to the target bioproduct(s). Also, bioconversion microorganisms must be able to tolerate the various inhibitors (such as furfural, hydroxymethylfurfural, acetic acid, phenolics) found in lignocellulosic hydrolysates. Projects in this theme are aimed at addressing both of these issues. In addition, we will develop a yeast strain capable of simultaneous hydrolysis and fermentation of pretreated lignocellulosic substrates. By engineering a microorganism with this capacity we aim to reduce enzyme use and thereby reduce the overall cost of the process.