Kristen Publicover, Tom Caldwell, and Sarah W. Harcum. Bioengineering, Clemson University, 51 New Cherry Street, 202 Biosystems Research Complex, Clemson, SC 29631
The success of biofuel ethanol economics is dominated by the final concentration of ethanol in the fermentation broth. The organism(s) used in the fermentation process must have high ethanol tolerance, as well as fast conversion rates. Saccharomyces bayanus is used industrially to produce wine, champagne, and ciders due to its high ethanol tolerance (up to 20% volume ethanol per volume liquid). Thus, we are currently investigating biofuel ethanol production using S. bayanus in a fed-batch fermentation system using very high gravity conditions. We have investigated culture pH, nitrogen levels, the use of minimal media, and initial cell densities. Another aspect related to biofuel ethanol production is the utilization of five-carbon sugars (such as xylose) by the yeast. Xylose is a major sugar that results from the hydrolyzed biomass; the other major sugar is glucose. S. bayanus cannot naturally metabolize xylose; however, it can metabolize xylulose. Xylulose can be enzymatically obtained from the xylose. Thus, we are investigating the enzymatic conversion of xylose to xylulose in conjunction with the ability of S. bayanus to metabolize xylulose. In these studies we are monitoring growth rates and ethanol production on xylulose in comparison to the growth rates and ethanol production from glucose. The efficient metabolism of both hexoses and pentoses by S. bayanus combined with its superior ethanol tolerance would be highly valuable for the economical production of ethanol from biomass sources such as switchgrass.
