Thursday, May 3, 2012: 2:00 PM
Napoleon Ballroom A and B, 3rd fl (Sheraton New Orleans)
Fermentation of cellulosic and hemicellulosic sugars from herbaceous or woody biomass could resolve food vs. fuel conflicts inherent in the bioconversion of grains. However, the inability to co-ferment glucose, xylose and cellobiose is a major challenge to the economical use of lignocellulose as a feedstock for renewable fuels. Simultaneous co-fermentation of glucose, xylose and cellobiose is problematic for almost all microbes – including yeasts that ferment xylose and cellobiose natively – because glucose represses utilization of other sugars. Surprisingly, the ascomyceteous, beetle associated yeast, Spathaspora passalidarum (1, 2), which ferments xylose and cellobiose natively, can also co-ferment these two sugars along with glucose. S. passalidarum, will simultaneously assimilate glucose and xylose aerobically; it will simultaneously co-ferment glucose, cellobiose and xylose under oxygen limitation with an ethanol yield of 0.42 g/g, and it has a specific ethanol production rate on xylose more than 3 times faster than the corresponding rate on glucose. Moreover, an adapted strain of S. passalidarum can produced 39 g/l ethanol with a yield of 0.43 g/g sugars from a maple wood hydrolysate. Metabolome analysis of S. passalidarum before onset and during the fermentations of glucose and xylose showed that the concentration of glycolytic intermediates is significantly higher on xylose than on glucose. These features make S. passalidarum very attractive for SSF applications and for studying regulatory mechanisms enabling bioconversion of lignocellulosic materials by yeasts.
References:
1. Nguyen NH, Suh SO, Marshall CJ, & Blackwell M (2006) Mycol. Res. 110:1232-1241
2. Wohlbach DJ, et al. (2011) PNAS 108(32):13212-13217.