Inhibitor tolerance of a recombinant flocculating industrial Saccharomyces cerevisiae strain during glucose and xylose co-fermentation

Abstract

Lignocellulose-derived inhibitors have negative effects on the ethanol fermentation capacity of Saccharomyces cerevisiae. In this study, the effects of eight typical inhibitors, including weak acids, furans, and phenols, on glucose and xylose co-fermentation of the recombinant xylose-fermenting flocculating industrial S. cerevisiae strain NAPX37 were evaluated by batch fermentation. Inhibition on glucose fermentation, not that on xylose fermentation, correlated with delayed cell growth. The weak acids and the phenols showed additive effects. The effect of inhibitors on glucose fermentation was as follows (from strongest to weakest): vanillin > phenol > syringaldehyde > 5-HMF > furfural > levulinic acid > acetic acid > formic acid. The effect of inhibitors on xylose fermentation was as follows (from strongest to weakest): phenol > vanillin > syringaldehyde > furfural > 5-HMF > formic acid > levulinic acid > acetic acid. The NAPX37 strain showed substantial tolerance to typical inhibitors and showed good fermentation characteristics, when a medium with inhibitor cocktail or rape straw hydrolysate was used. This research provides important clues for inhibitors tolerance of recombinant industrial xylose-fermenting S. cerevisiae.

Multi-Step Exploitation of Raw Arundo donax L. for the Selective Synthesis of Second-Generation Sugars by Chemical and Biological Route

“…Moreover, the formation of by-products was limited, even working at 17 wt%, being their concentrations in the range 0.5-1.3 g/L, except for AA that reached 4.7 g/L. Although the fermentability of the hydrolysates was not tested in this work, the by-product concentrations were lower than the typical inhibition thresholds [75]. This is certainly a positive key aspect, enabling the direct biological conversion of these hydrolysates, without additional further relevant detoxification procedures [46,47].…”

High Gravity Fermentation of Sugarcane Bagasse Hydrolysate by Saccharomyces pastorianus to Produce Economically Distillable Ethanol Concentrations: Necessity of Medium Components Examined

“…As expected, the reagent-grade sugar fermentations consumed the glucose and produced ethanol within about 35 h ( Figure 5), while the hydrolysate fermentations took approximately 55 h to completely consume the glucose and reach maximum ethanol levels. These data indicate that the inhibitor effects were minimal and S. pastorianus in the system was robust; whereas for native S. cerevisiae, tolerance is a sufficient concern that genomic approaches have been taken to try to solve the lack of inhibitor tolerance issue [23,[27][28][29]51]. Another positive attribute of this process is that the required inoculum was only 0.25 g dcw/L (0.5 OD), which represents a very low inoculum within the biofuels community [29,52].…”

“…These data indicate that the inhibitor effects were minimal and S. pastorianus in the system was robust; whereas for native S. cerevisiae, tolerance is a sufficient concern that genomic approaches have been taken to try to solve the lack of inhibitor tolerance issue [23,[27][28][29]51]. Another positive attribute of this process is that the required inoculum was only 0.25 g dcw/L (0.5 OD), which represents a very low inoculum within the biofuels community [29,52]. Further, the ethanol productivity reported in this study includes the growth phase as well as the production phase without the addition of yeast extract or peptone.…”

“…Many of these xylose metabolism modifications studies have not yet demonstrated higher ethanol productivity or ethanol concentrations, in part, due to using sugar concentrations that are too low in the fermentations [21,22]. Also, there have been recent gains in improving S. cerevisiae ethanol and inhibitor tolerance via recombinant means [23][24][25][26][27][28][29]. Complementary approaches have coupled cellobiose utilization with xylose utilization in recombinant S. cerevisiae with improved xylose to ethanol conversion rates [30].…”

Recombinant Diploid Saccharomyces cerevisiae Strain Development for Rapid Glucose and Xylose Co-Fermentation

“…Saccharomyces cerevisiae is the most effective microorganism for fermenting sugars to ethanol due to its rapid sugar consumption rate, high sugar and ethanol tolerance, and resistance to biomass-derived inhibitors [4,5]. Much research has been done to genetically engineer S. cerevisiae strains for xylose fermentation [6][7][8][9][10].…”