Pretreatment Affects Profits From Xylanase During Enzymatic Saccharification of Corn Stover Through Changing the Interaction Between Lignin and Xylanase Protein

Effective pretreatment is vital to improve the biomass conversion efficiency, which often requires the addition of xylanase as an accessory enzyme to enhance enzymatic saccharification of corn stover. In this study, we investigated the effect of two sophisticated pretreatment methods including ammonium sulfite (AS) and steam explosion (SE) on the xylanase profits involved in enzymatic hydrolysis of corn stover. We further explored the interactions between lignin and xylanase Xyn10A protein. Our results showed that the conversion rates of glucan and xylan in corn stover by AS pretreatment were higher by Xyn10A supplementation than that by SE pretreatment. Compared with the lignin from SE pretreated corn stover, the lignin from AS pretreated corn stover had a lower Xyn10A initial adsorption velocity (13.56 vs. 10.89 mg g−1 min−1) and adsorption capacity (49.46 vs. 27.42 mg g−1 of lignin) and weakened binding strength (310.6 vs. 215.9 L g−1). Our study demonstrated the low absolute zeta potential and strong hydrophilicity of the lignin may partly account for relative weak interaction between xylanase protein and lignin from AS pretreated corn stover. In conclusion, our results suggested that AS pretreatment weakened the inhibition of lignin to enzyme, promoted the enzymatic hydrolysis of corn stover, and decreased the cost of enzyme in bioconversion.

The advanced performance of microbial consortium for simultaneous utilization of glucose and xylose to produce lactic acid directly from dilute sulfuric acid pretreated corn stover

Background Lignocellulosic feedstocks have attracted much attention as a potential carbon source for lactic acid (LA) production because of their ready availability, sustainability, and renewability. However, there are at least two major technical challenges to producing LA from lignocellulose. Inhibitors derived from lignocellulose pretreatment have a negative impact on the growth of cells producing LA. Furthermore, pentose sugars produced from the pretreatment are difficultly utilized by most LA producers, which is known as the carbon catabolite repression (CCR) effect. This complex feedstock can be utilized by a robust microbial consortium with high bioconversion efficiency. Results In this study, a thermophilic consortium DUT50 producing LA was enriched and employed to improve corn stover (CS) utilization. Enterococcus was the dominant family in the consortium DUT50, accounting for 93.66% of the total abundance, with Lactobacillus, Bacillus, Lactococcus, and Trichococcus accounted for the remaining 2.68%. This consortium could be resistant to inhibitors concentration up to 9.74 g/L (2.88 g/L acetic acid, 2.46 g/L furfural, 2.20 g/L 5-HMF, and 2.20 g/L vanillin derived from pretreatment of CS), and simultaneously metabolizes hexose and pentose without CCR effect. Based on the promising consortium features, an efficient process of simultaneous saccharification and co-fermentation (SSCF) was developed to produce LA from acid pretreated corn stover, in which solid–liquid separation and detoxification were avoided. The key influencing factors were investigated and optimized, including dry biomass and cellulase loading, corn steep liquor powder concentration, and the pre-hydrolysis time. The highest LA titer of 71.04 g/L with a yield of 0.49 g/g-CS was achieved at a dry biomass loading of 20% (w/v), which is the highest LA production from non-detoxified acid pretreated corn stover via the SSCF process without wastewater generation reported to date. The simultaneous metabolism of hexose and pentose revealed collaboration between Enterococcus in the consortium, whereas xylose may be efficiently metabolized by Lactobacillus and Bacillus with low abundance via the pentose phosphate pathway. Conclusions The experimental results demonstrated the potential advantage of symbiosis in microbial consortia used for LA production from lignocellulosic biomass.

The Advanced Performance of Microbial Consortium for Simultaneous Utilization of Glucose and Xylose to Produce Lactic Acid Directly from Dilute Sulfuric Acid Pretreated Corn Stover

Background: Lignocellulosic feedstocks have attracted much attention as an alternative carbon source for lactic acid (LA) production with the advantages of ready availability, sustainability, and renewability. However, the production of LA from lignocellulose faces at least two major technical obstacles. The inhibitors derived from pretreatment of lignocellulose inhibit the growth of microorganism used in downstream hydrolysis and fermentation processes. In addition, most LA producers cannot to ferment pentose sugars and have carbon catabolite repression (CCR) effect. Microbial consortium with great robustness can use complex feedstocks displaying high bioconversion efficiency and has received great attention nowadays.Results: in this study, a thermophilic LA producing consortium DUT50 was enriched and employed to enhance the utilization of corn stover (CS). Enterococcus was the dominant family, accounting for 93.66% abundance in DUT50, and the abundance of Lactobacillus, Bacillus, Lactococcus and Trichococcus, accounted for 2.68% in total. This consortium was highly resistant to inhibitors up to 10.90 g/L derived from pretreatment of CS, metabolized hexose and pentose simultaneously without CCR effect. Based on consortium promising features, an efficient process of simultaneous saccharification and co-fermentation (SSCF) was developed to produce LA from acid-pretreated corn stover. The economical route avoided the operations of solid–liquid separation and detoxification. The key influential factors, including dry biomass and cellulase loading, corn steep liquor powder concentration, and the pre-hydrolysis time were investigated and optimized. The highest LA titer of 71.04 g/L with a yield of 0.49 g/g-CS was achieved at a dry biomass loading of 20% (w/v). This is the reported highest LA production from non-detoxified acid-pretreated corn stover via the SSCF process without wastewater generation. The interaction mode of Enterococcus was collaboration while the low abundance of Lactobacillus and Bacillus might metabolize xylose efficiently via the pentose phosphate pathway.Conclusions: Our results demonstrated the potential advantage of symbiosis and provided a feasible and economical route to produce LA from lignocellulosic biomass in industrial scale.

Chimeric cellobiohydrolase I expression, activity, and biochemical properties in three oleaginous yeast

Consolidated bioprocessing using oleaginous yeast is a promising modality for the economic conversion of plant biomass to fuels and chemicals. However, yeast are not known to produce effective biomass degrading enzymes naturally and this trait is essential for efficient consolidated bioprocessing. We expressed a chimeric cellobiohydrolase I gene in three different oleaginous, industrially relevant yeast: Yarrowia lipolytica, Lipomyces starkeyi, and Saccharomyces cerevisiae to study the biochemical and catalytic properties and biomass deconstruction potential of these recombinant enzymes. Our results showed differences in glycosylation, surface charge, thermal and proteolytic stability, and efficacy of biomass digestion. L. starkeyi was shown to be an inferior active cellulase producer compared to both the Y. lipolytica and S. cerevisiae enzymes, whereas the cellulase expressed in S. cerevisiae displayed the lowest activity against dilute-acid-pretreated corn stover. Comparatively, the chimeric cellobiohydrolase I enzyme expressed in Y. lipolytica was found to have a lower extent of glycosylation, better protease stability, and higher activity against dilute-acid-pretreated corn stover.