2-13: Comparing physiological responses to biomass-derived growth inhibitors between Clostridium thermocellum and Thermoanaerobacter pseudethanolicus 39E

Chemical and physical pretreatment of lignocellulosic biomass improves substrate reactivity but also releases microbial inhibitors such as furan aldehydes, low molecular weight fatty acids, and phenolic compounds. Microbial tolerance to such inhibitors is required for successful consolidated bioprocessing (CBP) of lignocellulosic biomass to biofuels. The cellulolytic thermophile, Clostridium thermocellum, is a CBP-candidate microbe and understanding its physiological response to different pretreatment inhibitors could aid in improving its CBP performance. Here we present results from systematic experiments to determine the effects of various biomass-derived aromatic aldehydes and alcohols, as well as the effect of media complexity on growth yield, kinetics, and end product formation. Data from C. thermocellum are compared to data from the related saccharolytic thermophile, Thermoanaerobacter pseudethanolicus 39E, which readily grows in the presence of biomass acid-hydrolysates. T. pseudethanolicus 39E grows with up to 4 g/L furfural present throughout growth, with addition of 1 and 2 g/L furfural actually stimulating growth. Similarly, T. pseudethanolicus 39E grows with up to 3 g/L 5-hydroxymethylfurfural (5-HMF). The presence of furan aldehydes does adversely affect substrate utilization, with 31 and 33 mM glucose utilized with 1.5 g/L furfural and 5-HMF respectively, versus 35 mM utilized with no furan aldehyde present. There is also more acetate (75.5 v. 65.5 mM) and less ethanol (~15 mM v. 30 mM) produced in the presence of furan aldehydes. Future work will characterize the effects of lignin-derived inhibitors on T. pseudethanolicus 39E and C. thermocellum and their respective fermentation performance.