Using a Designer Synthetic Media to Study Inhibitors Effect in Biomass Conversion
The biofuels industry has devoted significant efforts to converting lignocellulosic substrates into sugars that can be fermented into biofuels or other bioproducts. However, one of the major bottlenecks for cost-effective conversion in biorefineries has been the fermentation inhibition of yeast or bacteria by pretreatment degradation products. To engineer microbial strains for improved conversion, it is important to understand the inhibition mechanisms that affect the fermentative organisms in the presence of a lignocellulosic hydrolysate. One way in which these processes can be understood is by developing a synthetic hydrolysate media with a composition similar to the one that will be found after pretreating lignocellulosic biomass. Researchers at the Department of Energy’s Great Lakes Bioenergy Research Center characterized the plant-derived decomposition products present in ammonia fiber expansion (AFEX) pretreated corn stover hydrolsate (ACH), and a synthetic hydrolysate (SH) was formulated based on that ACH composition. The SH was used to evaluate the inhibitory effects of various families of decomposition products during fermentation using Saccharomyces cerevisiae strain 424A (LNH-ST). The SH did not entirely match the ACH performance; however, the major groups of inhibitory compounds were identified and used for further evaluation and comparison. Their characterization showed that the compounds present in ACH that were most inhibitory to fermentation were nitrogenous compounds, especially amides, though this result is associated with a concentration effect, given that nitrogenous compounds were the most abundant. Comparing inhibition due to amides in AFEX pretreatment versus inhibition due to carboxylic acids and other compounds formed in alternative pretreatment methods, they discovered that amides are significantly less inhibitory to both glucose and xylose fermentation. This means that ACH would be easily fermentable by yeast without any further detoxification. These studies help to map where to focus research efforts to overcome pretreatment byproduct inhibition of fermentation.
Tang, X., L. daCosta Sousa, M. Jin, S. P. S. Chundawat, C. K. Chambliss, M. W. Lau, Z. Xiao, B. E. Dale, and V. Balan. 2015. “Designer Synthetic Media for Studying Microbial-Catalyzed Biofuel Production,” Biotechnology for Biofuels 8:1. DOI: 10.1186/s13068-014-0179-6.