Glycerol supplementation of the growth medium enhances in situ detoxification of furfural by Clostridium beijerinckii during butanol fermentation

Abstract

Lignocellulose-derived microbial inhibitors such as furfural and 5-hydroxymethyl furfural adversely affect fermentation of lignocellulosic biomass hydrolysates to fuels and chemicals due to their toxicity on fermenting microbes. To harness the potential of lignocellulose as a cheap source of fermentable sugars, in situ detoxification of furfural and other lignocellulose-derived microbial inhibitors is essential. To enhance in situ detoxification and tolerance of furfural by Clostridium beijerinckii NCIMB 8052 during acetone-butanol-ethanol (ABE) fermentation, the effect of glycerol on NADH/NADPH generation and ABE production by furfural (4, 5, and 6 g/L)-challenged cultures was investigated in this study. In all instances, beneficial outcomes were observed. For example, the fermentation medium supplemented with glycerol and subjected to 5 g/L furfural elicited up to 1.8- and 3-fold increases, respectively, in NADH and NADPH levels in C. beijerinckii 8052 relative to the control culture. These critical changes are the likely underpinnings for the glycerol-mediated 2.3-fold increase in the rate of detoxification of 5 g/L furfural, substrate consumption, and ABE production compared to the unsupplemented medium. Collectively, these results demonstrate that increased intracellular NADH/NADPH in C. beijerinckii 8052 due to glycerol utilization engenders favorable effects on many aspects of cellular metabolism, including enhanced furfural reduction and increased ABE production.

Microbial inhibitors: formation and effects on acetone-butanol-ethanol fermentation of lignocellulosic biomass

“…Similar effects might occur to Clostridium species during ABE fermentation. The results of some studies (Ezeji et al 2007a;Qureshi et al 2010a;Ujor et al 2014;Zhang and Ezeji 2013;Zheng et al 2009b) also supported the similarity of toxicity effects between ABE and ethanol fermentation. Overall, the presence of these toxic compounds inhibited microbial cell growth and affected inhibition of glycolytic and fermentative enzymes, which are essential to central metabolic pathways.…”

“…They found that two enzymes encoded by Cbei_3974 and Cbei_3904 and belonging to the aldo/keto reductase and short-chain dehydrogenase/reductase families, respectively, were involved in furfural detoxification and tolerance. Moreover, recent studies (Qureshi et al 2012;Ujor et al 2014) found that the increase in HMF and furfural concentrations resulted in a decline in ABE (Fig. 7).…”

“…7). Ujor et al (2014) also investigated the effect of furfural with glycerol supplementation using C. beijerinckii NCIMB 8052 (Fig. 7).…”

“…For instance, furfural and HMF were converted into their alcoholic groups using NAD(P)Hs (Fig. 6) (Ujor et al 2014). These reduction processes ultimately affected redox equilibrium, thus the shift to the solventogenic phase was inhibited.…”

Allopurinol-mediated lignocellulose-derived microbial inhibitor tolerance by Clostridium beijerinckii during acetone–butanol–ethanol (ABE) fermentation

“…Since detoxification of furfural and HMF siphons NAD(P)H, thereby disrupting cellular redox balance and hampering cofactor-dependent biosynthetic reactions, we have been evaluating different strategies to enhance the availability of cellular reductants. For example, we recently reported that supplementation of the fermentation medium with glycerol, a more reduced substrate than glucose, led to a 2.3-fold increase in the rate of detoxification of 5 g/L furfural, substrate consumption, and acetone-butanol-ethanol (ABE) production by C. beijerinckii (Ujor et al 2014). We also showed that these benefits were likely due to the ability of glycerol to increase the NADH and NADPH levels by 1.8-and 3-fold, respectively.…”