Modulation of the Acetone/Butanol Ratio during Fermentation of Corn Stover-Derived Hydrolysate by Clostridium beijerinckii Strain NCIMB 8052

Abstract

Producing biobutanol from lignocellulosic biomass has shown promise to ultimately reduce greenhouse gases and alleviate the global energy crisis. However, because of the recalcitrance of a lignocellulosic biomass, a pretreatment of the substrate is needed which in many cases releases soluble lignin compounds (SLCs), which inhibit growth of butanol-producing clostridia. In this study, we found that SLCs changed the acetone/butanol ratio (A/B ratio) during butanol fermentation. The typical A/B molar ratio during Clostridium beijerinckii NCIMB 8052 batch fermentation with glucose as the carbon source is about 0.5. In the present study, the A/B molar ratio during batch fermentation with a lignocellulosic hydrolysate as the carbon source was 0.95 at the end of fermentation. Structural and redox potential changes of the SLCs were characterized before and after fermentation by using gas chromatography/mass spectrometry and electrochemical analyses, which indicated that some exogenous SLCs were involved in distributing electron flow to C. beijerinckii, leading to modulation of the redox balance. This was further demonstrated by the NADH/NAD ϩ ratio and trxB gene expression profile assays at the onset of solventogenic growth. As a result, the A/B ratio of end products changed significantly during C. beijerinckii fermentation using corn stover-derived hydrolysate as the carbon source compared to glucose as the carbon source. These results revealed that SLCs not only inhibited cell growth but also modulated the A/B ratio during C. beijerinckii butanol fermentation.IMPORTANCE Bioconversion of lignocellulosic feedstocks to butanol involves pretreatment, during which hundreds of soluble lignin compounds (SLCs) form. Most of these SLCs inhibit growth of solvent-producing clostridia. However, the mechanism by which these compounds modulate electron flow in clostridia remains elusive. In this study, the results revealed that SLCs changed redox balance by producing oxidative stress and modulating electron flow as electron donors. Production of H 2 and acetone was stimulated, while butanol production remained unchanged, which led to a high A/B ratio during C. beijerinckii fermentation using corn stover-derived hydrolysate as the carbon source. These observations provide insight into utilizing C. beijerinckii to produce butanol from a lignocellulosic biomass.

A global approach to obtain biobutanol from corn stover

“…The characteristics of this experimental design are shown in Table A1. The nutrients and their concentration ranges were selected according to literature data (Liu et al, 2017;Qureshi and Blaschek, 1999;Qureshi et al, 2014;Ujor et al, 2016).…”

“…In addition, polymeric resins potentiate the reduction of the overall production cost due to their reusability without affecting the process efficiency and in some cases without altering the sugar concentration contained in the hydrolysate (Gao and Rehmann, 2016). Previous studies on biobutanol production from corn stover have tried to solve each one of the abovementioned parameters through the selection of mutant and wild type solventogenic Clostridium strains (Liu et al, 2017;Qureshi et al, 2010;Tang et al, 2017;Wang and Chen, 2011;Xue et al, 2016a;Zhang et al, 2018); the use of different pretreatment reagents and conditions (Baral and Shah, 2017;Tang et al, 2017;Xue et al, 2016a;Zhang et al, 2014) and hydrolysate detoxification by various methods (Liu et al, 2017;Qureshi et al, 2010;Tang et al, 2017;Wang and Chen, 2011;Xue et al, 2016a;Zhang et al, 2018). Currently, studies conducted to potentiate biobutanol industrial production from corn stover are clearly required to increase yield values, but also to reduce the associated economic costs.…”

“…According to these results and taking into account both ABE concentrations and sugar consumption, it was decided to select the strain DSM 13864 for the optimisation experiments. Corn stover hydrolysates have been subjected to ABE fermentation employing several wild strains, such as C. acetobutylicum P262(Parekh et al, 1988), C. acetobutylicum zzu-02(Zhang et al, 2018), C. acetobutylicum ATCC 824 (=DSM 792)(Wang and Chen, 2011;Zhang et al, 2014), C. beijerinckii NCIMB 8052 (=CECT 508)(Liu et al, 2017), C. beijerinckii zzu-01(Zhang et al, 2018), C. beijerinckii P260(Qureshi et al, 2010;Qureshi et al, 2014) and C. saccharobutylicum DSM 13864(Xu et al, 2016); or modified strains, like C. acetobutylicumABE-P 1201 (Cai et al, 2017, C. beijerinckii CC101(Xue et al, 2016a) or C. beijerinckii NCIMB 4110(Tang et al, 2017). The selected strain in the present work(DSM 13864…”

Butanol–isopropanol fermentation with oxygen-tolerant Clostridium beijerinckii XH29

“…To release the inhibition of ABE fermentation, several detoxification methods have been developed. The over-liming method is an effective way to reduce the inhibition of ABE fermentation from lignocellulose hydrolysate (Liu et al 2017 ). Mutant strains with higher inhibitor tolerances have also been obtained by mutagenesis.…”

Reassessment of the role of CaCO3 in n-butanol production from pretreated lignocellulosic biomass by Clostridium acetobutylicum

“…Comprehensive studies on the responses of Clostridium strains in the Ca 2+ -containing real biomass hydrolysate, especially at molecular levels, are still very limited. Liu et al found that overliming removed the growth inhibitory effect of corn stover hydrolysate but was unable to eliminate the effects of soluble lignin compounds (SLC) on redox balance in C. beijerinckii , leading to a high acetone/butanol ratio 18 . It was also reported that thioredoxin reductase gene, trxB , was up-regulated in the late exponential phase, possibly to response to the increased oxidative stress caused by SLC 18 .…”