Drought-Stressed Switchgrass Hydrolysate Inhibit Microbial Biofuel Production

Drought affects lignocellulosic crop biomass yields and composition, and thus, biofuel yield. However, the effect of drought on downstream fermentation processes has never been directly described. To investigate the impact of climate variability on biofuel production, Michigan State University's Rebecca Garlock Ong and her team, collected corn stover and switchgrass for a period of 3 years with significantly different precipitation profiles.

All feedstocks were pretreated and hydrolyzed, and the hydrolysates were separately fermented using Saccharomyces cerevisiae and Zymomonas mobilis. Most corn stover and switchgrass hydrolysates were readily fermented. However, the growth of S. cerevisiae was completely inhibited in hydrolysate from drought-stressed switchgrass. Analysis found that strains deficient in genes related to protein trafficking within the cell were more resistant to the drought-stressed switchgrass hydrolysate. Further analysis revealed that drought-stressed switchgrass accumulated greater concentrations of soluble sugars in response to drought, and these sugars were then degraded during ammonia-based pretreatment.

Variations in environmental conditions during the growth of bioenergy crops were found to be capable of significant detrimental effects on fermentation organisms that are involved in biofuel production.