Switchgrass steroidal saponins that reduce fungal disease in the field inhibit yeast fermentation
Background/Objective
To determine the extent to which metabolite-mediated plant defense correlates with reduced fermentation in biofuel processing and to initiate approaches to overcome this challenge.
Approach
Scientists measured variation in field fungal infection, specialized metabolite production, and fermentation efficiency in 102 genotypes of switchgrass and investigated methods for rescuing fermentation for poorly fermenting lines.
Results
A limited number of steroidal saponins have a large influence on microbiome interactions. These compounds were found in the highest concentrations in the Atlantic switchgrass population, which exhibits low susceptibility in midwestern habitats to leaf rust, a dominant switchgrass pathogen. Similar compounds were associated with variation in both pathogenic leaf rust and fermentation yields with Saccharomyces cerevisiae. Bacterial fermentation using Zymomonas mobilis did not show the same inhibition. The addition of ergosterol also rescued yeast fermentation of recalcitrant switchgrass variants.
Impact
Increasing production of bioproducts from lignocellulosic feedstocks requires improvement in both field production and biorefinery efficiency, but the same metabolites that protect from fungal pathogens also limit fermentation. This study suggests that researchers can overcome these trade-offs by leveraging genetic diversity in biomass feedstocks and fermenting microbes.