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Transcriptional analysis of Clostridium beijerinckii NCIMB 8052 to elucidate role of furfural stress during acetone butanol ethanol fermentation.

ABSTRACT: BACKGROUND: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. RESULTS:A 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. CONCLUSION:Genome-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.

SUBMITTER: Zhang Y

PROVIDER: S-EPMC3681630 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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Transcriptional analysis of Clostridium beijerinckii NCIMB 8052 to elucidate role of furfural stress during acetone butanol ethanol fermentation.

Zhang Yan Y Ezeji Thaddeus Chukwuemeka TC

Biotechnology for biofuels 20130504 1

<h4>Background</h4>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 ...[more]

PMID: 23642190

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Project description: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+ 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 H2 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.

Project description:BackgroundSolventogenic clostridia offer a sustainable alternative to petroleum-based production of butanol--an important chemical feedstock and potential fuel additive or replacement. C. beijerinckii is an attractive microorganism for strain design to improve butanol production because it (i) naturally produces the highest recorded butanol concentrations as a byproduct of fermentation; and (ii) can co-ferment pentose and hexose sugars (the primary products from lignocellulosic hydrolysis). Interrogating C. beijerinckii metabolism from a systems viewpoint using constraint-based modeling allows for simulation of the global effect of genetic modifications.ResultsWe present the first genome-scale metabolic model (iCM925) for C. beijerinckii, containing 925 genes, 938 reactions, and 881 metabolites. To build the model we employed a semi-automated procedure that integrated genome annotation information from KEGG, BioCyc, and The SEED, and utilized computational algorithms with manual curation to improve model completeness. Interestingly, we found only a 34% overlap in reactions collected from the three databases--highlighting the importance of evaluating the predictive accuracy of the resulting genome-scale model. To validate iCM925, we conducted fermentation experiments using the NCIMB 8052 strain, and evaluated the ability of the model to simulate measured substrate uptake and product production rates. Experimentally observed fermentation profiles were found to lie within the solution space of the model; however, under an optimal growth objective, additional constraints were needed to reproduce the observed profiles--suggesting the existence of selective pressures other than optimal growth. Notably, a significantly enriched fraction of actively utilized reactions in simulations--constrained to reflect experimental rates--originated from the set of reactions that overlapped between all three databases (P = 3.52 × 10-9, Fisher's exact test). Inhibition of the hydrogenase reaction was found to have a strong effect on butanol formation--as experimentally observed.ConclusionsMicrobial production of butanol by C. beijerinckii offers a promising, sustainable, method for generation of this important chemical and potential biofuel. iCM925 is a predictive model that can accurately reproduce physiological behavior and provide insight into the underlying mechanisms of microbial butanol production. As such, the model will be instrumental in efforts to better understand, and metabolically engineer, this microorganism for improved butanol production.

Project description:Furfural is the prevalent microbial inhibitor generated during pretreatment and hydrolysis of lignocellulosic biomass to monomeric sugars, but the molecular response of Clostridium beijerinckii NCIMB 8052 to this compound is unknown. To discern the effect of furfural on C. beijerinckii and to gain insights into the molecular mechanisms of action and detoxification, we studied the physiological changes of furfural-stressed cultures during acetone-butanol-ethanol (ABE) fermentation, and profiled differentially expressed genes by genome-wide transcriptional analysis. C. beijerinckii exposed to furfural stress during the acidogenic growth phase produced 13% more ABE than the unstressed control. The growth and ABE by C. beijerinckii ceased following exposure to furfural stress during the solventogenic growth phase. By comparing gene expression of furfural-stressed cultures to that of the unstressed control, at both the acidogenic and solventogenic phases, we ascertained that furfural induces expression of several genes including those that code for heat shock proteins, redox enzymes and cofactor associated proteins, and ATP-binding cassette transporters, and represses genes belonging to the phosphotransferase system, two-component system, chemotaxis and cell motility. Based on these results, we discuss the underpinning for furfural-mediated change in ABE fermentation by the solventogenic Clostridium species. C. beijerinckii 8052 pre-culture was incubated anaerobically to attain acidogenic or solventogenic growth phase. The culture was then subdivided into two bottles. One bottle was challenged with furfural and the other bottle was left unchallenged. After 3 h growth, C. beijerinckii 8052 samples were collected, during which the original concentration of furfural in the growth medium was reduced to more than half. Total RNA was isolated, purified, converted to enriched mRNA, and dye-coupled (Alexa Fluor 555) complementary cRNA. This was followed by hybridization and microarray data analysis.

Dataset Information

Transcriptional analysis of Clostridium beijerinckii NCIMB 8052 to elucidate role of furfural stress during acetone butanol ethanol fermentation.

Publications

Transcriptional analysis of Clostridium beijerinckii NCIMB 8052 to elucidate role of furfural stress during acetone butanol ethanol fermentation.

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