17-35: Co-fermentation of glucose and xylose for ethanol production from hydrolysates by adapted native xylose-fermenting yeast Spathaspora passalidarum

Spathaspora passalidarum is a beetle-associated yeast that natively ferments xylose and cellobiose to ethanol.  The wild-type strain (NRRL Y-27907) (1) produces ethanol with rates and yields similar to those found with Scheffersomyces stipitis. In addition, S. passalidarum exhibits unusual regulatory properties that make it of particular interest for further development. By applying directed evolution to S. passalidarum, two adapted S. passalidarum strains AF8 and E7 both showed co-utilization of glucose and xylose in AFEX corn stover and maple hydrolysates.  The parental strain AF2 can only tolerate 1.4 g/l of acetic acid but AF8 is able to ferment 93% of raw AFEX hydrolysate containing 10% of monosaccharide and 2.2 g/l of acetic acid. The maximum ethanol productivity of AF8 is about 2.5 times higher than the parental adapted strain AF2.  The other adapted strain E7 showed the ability to produce about 38 g/l ethanol from maple hydrolysate medium containing 65g/l of xylose and 35 g/l of glucose in 59h in 2-l bioreactors.  The ethanol yields from AFEX corn stover and maple hydrolysate were 0.33 and 0.38, respectively. Our results showed that adaption can improve strains performance and adapted S. passalidarum can still co-ferment glucose and xylose in hydrolysates.

1. Nguyen NH, Suh SO, Marshall CJ, & Blackwell M (2006) Morphological and ecological similarities: wood-boring beetles associated with novel xylose-fermenting yeasts, Spathaspora passalidarum gen. sp nov and Candida jeffriesii sp nov. Mycological Research 110:1232-1241.