Tuesday, April 30, 2013
Exhibit Hall
Recombinant Saccharomyces cerevisiae strains with the ability to ferment xylose to ethanol enhance the value of ethanol production processes from plant biomass. In the ICM cellulosic ethanol process, feed stocks are pre-treated and enzymatically hydrolyzed, resulting in a fiber hydrolysate. Hydrolysates are then fermented by recombinant yeasts for ethanol production. A variety of xylose-fermenting S. cerevisiae strains are now available from various yeast companies operating in the biofuels space. This work describes our approach to testing available yeast strains for fitness to our process. Testing criteria for yeasts included: i. ability to quickly grow on inexpensive industrial media, ii. tolerance to hydrolysate inhibitors, iii. ability to ferment glucose and xylose quickly and efficiently under process conditions. A battery of testing media was utilized in a shake flask format first, and the best yeast candidates were re-screened in bench top fermentations, prior to final validation at pilot plant scale. Our results showed that while all tested yeasts fermented xylose to ethanol, only a few appeared robust enough to withstand the requirements of our process. A discussion is presented on the wide range of observed yeast behavior towards media and process conditions, and its perceived impact on fitness to the ICM process.