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Biotechnol Biofuels. 2015 Jan 22;8(1):1. doi: 10.1186/s13068-014-0179-6. eCollection 2015.

Designer synthetic media for studying microbial-catalyzed biofuel production.

Author information

1
Biogas Institute of Ministry of Agriculture, Section 4-13 Remin South Road, Chengdu, 610041 P. R. China.
2
DOE Great Lakes Bioenergy Research Center, Biomass Conversion Research Lab (BCRL), Chemical Engineering and Materials Science, Michigan State University, 3815 Technology Boulevard, Suite 1045, Lansing, 48910 USA.
3
DOE Great Lakes Bioenergy Research Center, Biomass Conversion Research Lab (BCRL), Chemical Engineering and Materials Science, Michigan State University, 3815 Technology Boulevard, Suite 1045, Lansing, 48910 USA ; Department of Chemical & Biochemical Engineering, Rutgers, The State University of New Jersey, 98 Brett Road, Room C-150A, Piscataway, NJ 08854 USA.
4
Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798 USA.
5
School of Chemical Engineering, Sichuan University, No. 24 South Section 1, Yihuan Road, Chengdu, 610065 P. R. China.

Abstract

BACKGROUND:

The fermentation inhibition of yeast or bacteria by lignocellulose-derived degradation products, during hexose/pentose co-fermentation, is a major bottleneck for cost-effective lignocellulosic biorefineries. To engineer microbial strains for improved performance, it is critical to understand the mechanisms of inhibition that affect fermentative organisms in the presence of major components of a lignocellulosic hydrolysate. The development of a synthetic lignocellulosic hydrolysate (SH) media with a composition similar to the actual biomass hydrolysate will be an important advancement to facilitate these studies. In this work, we characterized the nutrients and plant-derived decomposition products present in AFEX™ pretreated corn stover hydrolysate (ACH). The SH was formulated based on the ACH composition and was further used to evaluate the inhibitory effects of various families of decomposition products during Saccharomyces cerevisiae 424A (LNH-ST) fermentation.

RESULTS:

The ACH contained high levels of nitrogenous compounds, notably amides, pyrazines, and imidazoles. In contrast, a relatively low content of furans and aromatic and aliphatic acids were found in the ACH. Though most of the families of decomposition products were inhibitory to xylose fermentation, due to their abundance, the nitrogenous compounds showed the most inhibition. From these compounds, amides (products of the ammonolysis reaction) contributed the most to the reduction of the fermentation performance. However, this result is associated to a concentration effect, as the corresponding carboxylic acids (products of hydrolysis) promoted greater inhibition when present at the same molar concentration as the amides. Due to its complexity, the formulated SH did not perfectly match the fermentation profile of the actual hydrolysate, especially the growth curve. However, the SH formulation was effective for studying the inhibitory effect of various compounds on yeast fermentation.

CONCLUSIONS:

The formulation of SHs is an important advancement for future multi-omics studies and for better understanding the mechanisms of fermentation inhibition in lignocellulosic hydrolysates. The SH formulated in this work was instrumental for defining the most important inhibitors in the ACH. Major AFEX decomposition products are less inhibitory to yeast fermentation than the products of dilute acid or steam explosion pretreatments; thus, ACH is readily fermentable by yeast without any detoxification.

KEYWORDS:

AFEX; Amides inhibition; Carboxylic acids inhibition; Hydrolysate composition; Lignocellulose; Pretreatment decomposition products; Synthetic hydrolysate; Yeast fermentation inhibition

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