Abstract
BackgroundFurfural is the prevalent microbial inhibitor generated during pretreatment and hydrolysis of lignocellulose biomass to monomeric sugars, but the response of acetone butanol ethanol (ABE) producing Clostridium beijerinckii NCIMB 8052 to this compound at the molecular level is unknown. To discern the effect of furfural on C. beijerinckii and to gain insight into molecular mechanisms of action and detoxification, physiological changes of furfural-stressed cultures during acetone butanol ethanol (ABE) fermentation were studied, and differentially expressed genes were profiled by genome-wide transcriptional analysis.ResultsA total of 5,003 C. beijerinckii NCIMB 8052 genes capturing about 99.7% of the genome were examined. About 111 genes were differentially expressed (up- or down-regulated) by C. beijerinckii when it was challenged with furfural at acidogenic growth phase compared with 721 genes that were differentially expressed (up- or down-regulated) when C. beijerinckii was challenged with furfural at solventogenic growth phase. The differentially expressed genes include genes related to redox and cofactors, membrane transporters, carbohydrate, amino sugar and nucleotide sugar metabolisms, heat shock proteins, DNA repair, and two-component signal transduction system. While C. beijerinckii exposed to furfural stress during the acidogenic growth phase produced 13% more ABE than the unstressed control, ABE production by C. beijerinckii ceased following exposure to furfural stress during the solventogenic growth phase.ConclusionGenome-wide transcriptional response of C. beijerinckii to furfural stress was investigated for the first time using microarray analysis. Stresses emanating from ABE accumulation in the fermentation medium; redox balance perturbations; and repression of genes that code for the phosphotransferase system, cell motility and flagellar proteins (and combinations thereof) may have caused the premature termination of C. beijerinckii 8052 growth and ABE production following furfural challenge at the solventogenic phase.This study provides insights into basis for metabolic engineering of C. beijerinckii NCIMB 8052 for enhanced tolerance of lignocellulose-derived microbial inhibitory compounds, thereby improving bioconversion of lignocellulose biomass hydrolysates to biofuels and chemicals. Indeed, two enzymes encoded by Cbei_3974 and Cbei_3904 belonging to aldo/keto reductase (AKR) and short-chain dehydrogenase/reductase (SDR) families have been identified to be involved in furfural detoxification and tolerance.
Highlights
Clostridium species are gram positive, anaerobic, sporeforming bacteria [1]
Production of acetone butanol ethanol (ABE) by solventogenic Clostridium species is attractive by virtue of their ability to utilize sugars such as cellobiose, glucose, xylose, arabinose and mannose that are present in lignocellulosic biomass hydrolysate
Why microarray analysis of C. beijerinckii 8052 transcriptome under furfural stress? Furfural was chosen as archetypical lignocellulose-derived inhibitory compound for this investigation because it is the most prevalent microbial inhibitor generated during pretreatment and hydrolysis of lignocellulosic biomass to monomeric sugars
Summary
Clostridium species are gram positive, anaerobic, sporeforming bacteria [1]. Production of ABE (acetone-butanolethanol) by solventogenic Clostridium species is attractive by virtue of their ability to utilize sugars such as cellobiose, glucose, xylose, arabinose and mannose that are present in lignocellulosic biomass hydrolysate. Butanol production from lignocellulosic biomass has shown promise, and the feedstock is abundant, renewable and relatively cheap [2] Microbial inhibitors, such as furfural, hydroxymethylfurfural (HMF), hydroxybenzaldehyde, and coumaric acid, are produced during lignocellulosic biomass pretreatment and these compounds impede biofuel production from generated hydrolysates [2]. Furfural is the prevalent microbial inhibitor generated during pretreatment and hydrolysis of lignocellulose biomass to monomeric sugars, but the response of acetone butanol ethanol (ABE) producing Clostridium beijerinckii NCIMB 8052 to this compound at the molecular level is unknown. To discern the effect of furfural on C. beijerinckii and to gain insight into molecular mechanisms of action and detoxification, physiological changes of furfural-stressed cultures during acetone butanol ethanol (ABE) fermentation were studied, and differentially expressed genes were profiled by genome-wide transcriptional analysis
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