Clostridium Saccharoperbutylacetonicum N1-4 Research Articles

Extractive Fed-Batch Bioacetone Fermentation with Free Cell and Immobilized Clostridium Saccharoperbutylacetonicum N1-4 in a Large Extractant Volume

Extractive Fed-Batch Bioacetone Fermentation with Free Cell and Immobilized Clostridium Saccharoperbutylacetonicum N1-4 in a Large Extractant Volume

Feasibility of Efficient, Direct, Butanol Production from Food Waste without Nutrient Supplement by Clostridium saccharoperbutylacetonicum N1-4

This study investigated the feasibility of direct butanol production from starchy food waste (without saccharification and nutrient supplementation). First, Clostridium saccharoperbutylacetonicum N1-4 was selected as an efficient starch-utilizing clostridia, and amylose was used by the strain more readily than amylopectin for solvent production. Furthermore, direct fermentation avoided substrate inhibition due to saccharification and produced 12.1 g/L of butanol at a production rate of 0.705 g/L/h and a yield of 0.402 C-mol/C-mol with a solid–liquid ratio of 1:1 (w/v). At a solid–liquid ratio of 1:2 (w/v), the maximum butanol production rate in the direct mode was 2.05 times higher than that in the saccharified mode. Elemental analysis demonstrated that the food waste analyzed was rich in trace elements and, hence, exogenous nutrient supplementation was unnecessary. Collectively, direct butanol production from food waste could function as a low-cost, highly efficient, and simple fermentative process, which is a promising strategy for food waste disposal.

Production of acetone, butanol, and ethanol by electro-fermentation with Clostridium saccharoperbutylacetonicum N1-4

This manuscript describes the effect of altering the extracellular redox potential during the production of acetone, butanol, and ethanol on a dual chamber H-type microbial fuel cell by fermenting glucose with Clostridium saccharoperbutylacetonicum N1-4. Extracellular redox potential modification was achieved by either supplementing the microbial broth with the redox agent NADH or by poising the cathode potential at −600 mV vs. Ag/AgCl. The addition of NADH was found to foment the production of acetone via fermentation of glucose. The addition of 200 mM of NADH to the catholyte rendered the highest production of acetone (2.4 g L-1), thus outperforming the production of acetone by conventional fermentation means (control treatment) by a factor of 2.2. The experimental evidence gathered here, indicates that cathodic electro-fermentation of glucose favors the production of butanol. When poising the cathode potential at −600 mV vs Ag/AgCl (electro-fermentation), the largest production of butanol was achieved (5.8 g L-1), outperforming the control treatment by a factor of 1.5. The production of ABE solvents and the electrochemical measurements demonstrate the electroactive properties of C. saccharoperbutylacetonicum N1-4 and illustrates the usefulness of bio-electrochemical systems to improve conventional fermentative processes.

Inorganic Carbon Assimilation and Electrosynthesis of Platform Chemicals in Bioelectrochemical Systems (BESs) Inoculated with Clostridium saccharoperbutylacetonicum N1-H4.

The need for greener processes to satisfy the demand of platform chemicals together with the possibility of reusing CO2 from human activities has recently encouraged research on the set-up, optimization, and development of bioelectrochemical systems (BESs) for the electrosynthesis of organic compounds from inorganic carbon (CO2, HCO3-). In the present study, we tested the ability of Clostridium saccharoperbutylacetonicum N1-4 (DSMZ 14923) to produce acetate and D-3-hydroxybutyrate from inorganic carbon present in a CO2:N2 gas mix. At the same time, we tested the ability of a Shewanella oneidensis MR1 and Pseudomonas aeruginosa PA1430/CO1 consortium to provide reducing power to sustain carbon assimilation at the cathode. We tested the performance of three different systems with the same layouts, inocula, and media, but with the application of 1.5 V external voltage, of a 1000 Ω external load, and without any connection between the electrodes or external devices (open circuit voltage, OCV). We compared both CO2 assimilation rate and production of metabolites (formate, acetate 3-D-hydroxybutyrate) in our BESs with the values obtained in non-electrogenic control cultures and estimated the energy used by our BESs to assimilate 1 mol of CO2. Our results showed that C. saccharoperbutylacetonicum NT-1 achieved the maximum CO2 assimilation (95.5%) when the microbial fuel cells (MFCs) were connected to the 1000 Ω external resistor, with the Shewanella/Pseudomonas consortium as the only source of electrons. Furthermore, we detected a shift in the metabolism of C. saccharoperbutylacetonicum NT-1 because of its prolonged activity in BESs. Our results open new perspectives for the utilization of BESs in carbon capture and electrosynthesis of platform chemicals.

Polycationic Surfaces Promote Whole-Cell Immobilization and Induce Microgranulation of Clostridium saccharoperbutylacetonicum N1-4 for Enhanced Biobutanol Production.

Immobilization is a common strategy used to protect microbial cells to improve the performance of bioprocesses. However, the interaction mechanism between the cells and the immobilization material is generally poorly understood. In this study, we employed natural polysaccharide-based materials as immobilization carriers for clostridial fermentation in an attempt to enhance the production of butanol (a valuable biofuel/biochemical but highly toxic to the host cells) and meanwhile elucidate the interaction mechanisms related to immobilization. The utilization of chitosan powder as the immobilization carrier enhanced butanol productivity by 97% in the fermentation with Clostridium saccharoperbutylacetonicum N1-4 and improved butanol titer by 21% in the fermentation with Clostridium beijerinckii NCIMB 8052. Additionally, analogue derivatives using microcrystalline cellulose (MCC) and cotton cationized on the surface with 3-chloro-2-hydroxypropyltrymethylammonium (CHPTA) and 2-chloro-N,N-diethylaminoethyl chloride (DEAEC) were prepared and used as immobilization carriers for similar fermentation conditions. The CHPTA derivatives showed slightly increased production of butanol and total solvent with C. saccharoperbutylacetonicum. Overall, our results indicated that the interaction between the cell and the carrier material occurs through a double mechanism involving adsorption immobilization and induced aggregation. This work provides insights concerning the effects of the chemical properties of the carrier material (such as the cation density and surface area) on fermentation performance, enabling a better understanding of the interaction between bacterial cells and the cationic materials. The derivatization strategies employed in this study can be applied to most cellulosic materials to modulate the properties and enhance the interaction between the cell and the carrier material for immobilization, thus improving the bioprocess performance.

Trends in Synthetic Biology in the Bioeconomy of Non-Food-Competing Biofuels

Despite the acknowledged relevance of renewable energy sources, biofuel production supported by food-related agriculture has faced severe criticism. One way to minimize the considered negative impacts is the use of sources of non-food biomass or wastes. Synthetic biology (SB) embraces a promising complex of technologies for biofuel production from non-edible and sustainable raw materials. Therefore, it is pertinent to identify the global evolution of investments, concepts, and techniques underlying the field in support of policy formulations for sustainable bioenergy production. We mapped the SB scientific knowledge related to biofuels using software that combines information visualization methods, bibliometrics, and data mining algorithms. The United States and China have been the leading countries in developing SB technologies. The Technical University of Denmark and Tsinghua University are institutions with higher centrality and have played prominent roles besides UC Los Angeles and Delft University Technology. We identified six knowledge clusters under the terms: versatile sugar dehydrogenase, redox balance principle, sesquiterpene production, Saccharomyces cerevisiae, recombinant xylose-fermenting strain, and Clostridium saccharoperbutylacetonicum N1-4. The emerging trends refer to specific microorganisms, processes, and products. Yarrowia lipolytica, Oleaginous yeast, E. coli, Klebsiella pneumoniae, Phaeodactylum tricornutum, and Microalgae are the most prominent microorganisms, mainly from the year 2016 onward. Anaerobic digestion, synthetic promoters, and genetic analysis appear as the most relevant platforms of new processes. Improved biofuels, bioethanol, and N-butanol are at the frontier of the development of SB-derived products. Synthetic biology is a dynamic interdisciplinary field in environmentally friendly bioenergy production pushed by growing social concerns and the emergent bioeconomy.

Increased Butyrate Production in Clostridium saccharoperbutylacetonicum from Lignocellulose-Derived Sugars.

Butyrate is produced by chemical synthesis based on crude oil, produced by microbial fermentation, or extracted from animal fats (M. Dwidar, J.-Y. Park, R. J. Mitchell, and B.-I. Sang, The Scientific World Journal, 2012:471417, 2012, https://doi.org/10.1100/2012/471417). Butyrate production by anaerobic bacteria is highly favorable since waste or sustainable resources can be used as the substrates. For this purpose, the native hyper-butanol producer Clostridium saccharoperbutylacetonicum N1-4(HMT) was used as a chassis strain due to its broad substrate spectrum. BLASTp analysis of the predicted proteome of C. saccharoperbutylacetonicum N1-4(HMT) resulted in the identification of gene products potentially involved in acetone-butanol-ethanol (ABE) fermentation. Their participation in ABE fermentation was either confirmed or disproven by the parallel production of acids or solvents and the respective transcript levels obtained by transcriptome analysis of this strain. The genes encoding phosphotransacetylase (pta) and butyraldehyde dehydrogenase (bld) were deleted to reduce acetate and alcohol formation. The genes located in the butyryl-CoA synthesis (bcs) operon encoding crotonase, butyryl-CoA dehydrogenase with electron-transferring protein subunits α and β, and 3-hydroxybutyryl-CoA dehydrogenase were overexpressed to channel the flux further towards butyrate formation. Thereby, the native hyper-butanol producer C. saccharoperbutylacetonicum N1-4(HMT) was converted into the hyper-butyrate producer C. saccharoperbutylacetonicum ΔbldΔpta [pMTL83151_BCS_PbgaL]. The transcription pattern following deletion and overexpression was characterized by a second transcriptomic study, revealing partial compensation for the deletion. Furthermore, this strain was characterized in pH-controlled fermentations with either glucose or Excello, a substrate yielded from spruce biomass. Butyrate was the main product, with maximum butyrate concentrations of 11.7 g·L-1 and 14.3 g·L-1, respectively. Minimal amounts of by-products were detected. IMPORTANCE Platform chemicals such as butyrate are usually produced chemically from crude oil, resulting in the carry-over of harmful compounds. The selective production of butyrate using sustainable resources or waste without harmful by-products can be achieved by bacteria such as clostridia. The hyper-butanol producer Clostridium saccharoperbutylacetonicum N1-4(HMT) was converted into a hyper-butyrate producer. Butyrate production with very small amounts of by-products was established with glucose and the sustainable lignocellulosic sugar substrate Excello extracted from spruce biomass by the biorefinery Borregaard (Sarpsborg, Norway).

Modelling and Simulation of Biobutanol Fermentation by Clostridium saccharoperbutylacetonicum N1-4

Biobutanol exhibits high octane number, non-hygroscopic, non-corrosive and can be mixed with gasoline without engine modification. Furthermore, the use of biobutanol as a fuel can reduce the negative impact of environmental due to the use of fossil-based fuel. Therefore, research on the development of biobutanol is still very much needed, including research on modelling and simulation of biobutanol production by fermentation. With modelling and simulation, we can predict various biobutanol production behaviour. This paper deals with the modelling and simulation of the production of biobutanol from glucose in batch bioreactor using Clostridium saccharoperbutylacetonicum N1-4. C. saccharoperbutylacetonicum N1-4 exhibits a good growth ability on simple or complex sugars, such as glucose, sucrose, or starch. This study concerned with the kinetics models of biobutanol production as developed by Shinto based on the C. acetobutylicum metabolic pathway which consists of the glycolysis, acidogenesis and solventogenesis pathways with several simplification of reactions. In this study, modelling was carried out by adapting the rate parameter value of k13 indicating the rate constant of cell death. The adapted models were applied to determine the effect of the initial concentration of glucose and organic acids on the production of butanol and compared to the experimental data from previous research. Model simulations were performed by using MATLAB® software. The butanol yield was affected by the initial glucose concentration. The highest butanol yield of 77% was obtained at a glucose concentration of 22 g/L. The simulation results exhibit that the biobutanol yield decreases when the glucose concentration is higher than 22 g/L. These results are consistent with previous experimental data. The simulation results also show the effect of the concentration of acetic acid in the fermentation medium and can be optimized. From the simulation results, the presence of 7.5 g/L acetic acid can increase the biobutanol production by 20%. However, previous experimental data showed that a concentration of 2.5 g/L acetic acid was preferred. The simulation results also show the effect of the addition of butyric acid and lactic acid on the production of biobutanol.

Identification and Investigation of Autolysin Genes in Clostridium saccharoperbutylacetonicum Strain N1-4 for Enhanced Biobutanol Production.

Biobutanol is a valuable biochemical and one of the most promising biofuels. Clostridium saccharoperbutylacetonicum N1-4 is a hyperbutanol-producing strain. However, its strong autolytic behavior leads to poor cell stability, especially during continuous fermentation, thus limiting the applicability of the strain for long-term and industrial-scale processes. In this study, we aimed to evaluate the role of autolysin genes within the C. saccharoperbutylacetonicum genome related to cell autolysis and further develop more stable strains for enhanced butanol production. First, putative autolysin-encoding genes were identified in the strain based on comparison of amino acid sequence with homologous genes in other strains. Then, by overexpressing all these putative autolysin genes individually and characterizing the corresponding recombinant strains, four key genes were pinpointed to be responsible for significant cell autolysis activities. Further, these key genes were deleted using CRISPR-Cas9. Fermentation characterization demonstrated enhanced performance of the resultant mutants. Results from this study reveal valuable insights concerning the role of autolysins for cell stability and solvent production, and they provide an essential reference for developing robust strains for enhanced biofuel and biochemical production.IMPORTANCE Severe autolytic behavior is a common issue in Clostridium and many other microorganisms. This study revealed the key genes responsible for the cell autolysis within Clostridium saccharoperbutylacetonicum, a prominent platform for biosolvent production from lignocellulosic materials. The knowledge generated in this study provides insights concerning cell autolysis in relevant microbial systems and gives essential references for enhancing strain stability through rational genome engineering.

BIOBUTANOL PRODUCTION USING FED-BATCH HIGH CELL DENSITY EXTRACTIVE FERMENTATION

Butanol, as a product with specific toxicity for its producer, is necessary to be maintained in low concentration during fermentation. In-situ integrated recovery using extensive volume extraction was used in high cell density fermentation in order to prevent the lag phase in the prime condition. Clostridium saccharoperbutylacetonicum N1-4 ATCC 13564 was employed to ferment glucose in extractive fermentation with oleyl alcohol as extractant. As the results of fed-batch cultures using high cell density with different extractant to broth volume ratios (Ve/Vb), 0.8 g/l butanol concentration in the broth was maintained with a ratio of 10, which was much lower than 4.4 g/l with the ratio of 0.5. Besides, the Ve/Vb ratio of 10 demonstrated 2.7-fold higher total butanol concentration (28 g/l) than that 11 g/l obtained with a Ve/Vb ratio of 0.5. These results indicated that larger Ve/Vb improved total butanol concentration by reducing butanol toxicity in broth.

Carboxylated-cellulose nanofibers from oil palm empty fruit bunches enhanced extractive fermentation in microbial biobutanol production

Nanocellulose produced by 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (TEMPO)-catalyzed oxidation, described as TEMPO-oxidized cellulose nanofibers (TOCNs), has a high density of negative charges on its surface. Its use in microbial fermentation systems is expected to be beneficial. In particular, microbial stability is required in acetone–butanol–ethanol (ABE) fermentation. Here, TOCNs derived from oil palm empty fruit bunches pulp were added to extractive ABE fermentation media, followed by microbial fermentation. The results showed that the presence of TOCNs induced higher total butanol production in broth by improving the growth environment of Clostridium saccharoperbutylacetonicum N1-4, which was used as the butanol-producing strain. Electrostatic repulsion between anionic surface carboxylate groups of TOCNs and negatively-charged bacteria made a positive contribution to the microenvironment for bacterial growth. The addition of TOCNs to fermentation media had significant positive effects on the total butanol yield density cell weight (DCW).

Nanocellulose from oil palm biomass to enhance microbial fermentation of butanol for bioenergy applications

Nanocellulose made by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-catalyzed oxidation, described as TEMPO-oxidized cellulose nanofibers (TOCNs), has a high density of negative charges on its surface. Its use in microbial fermentation systems is expected to benefit microbial process stability. In particular, microbial stability is strongly required in acetone–butanol–ethanol (ABE) fermentation associated with the solvent-extraction process of butanol production. Here, TOCNs derived from oil palm empty fruit bunches pulp were added to extractive ABE fermentation media containing glucose as a main source, which can be potentially obtained from biomass by saccharification. Then, microbial fermentation was carried out using free or immobilized bacterial cells, to produce butanol from glucose. The presence of TOCNs induced higher total butanol production in broth by improving the growth environment of Clostridium saccharoperbutylacetonicum N1-4, which was used as the butanol-producing strain. Microscopic analysis revealed that the spider-web-like TOCN network helped to entrap bacterial cells in alginate beads, by ionic crosslinking of TOCNs and alginates via Ca2+ ions, to increase stability of bacterial cells in the composite gel beads. The addition of TOCNs to fermentation media had significant positive effects on the total butanol yield.

Highly efficient continuous acetone–butanol–ethanol production from mixed sugars without carbon catabolite repression

Factors including the composition and concentration of mixed sugars, dilution rate, and cell density were examined to establish a highly efficient continuous acetone–butanol–ethanol (ABE) fermentation process using Clostridium saccharoperbutylacetonicum N1-4. During conventional continuous fermentation at a dilution rate of 0.15 h−1, the glucose/xylose mixture exhibited carbon catabolite repression (CCR) with an intensity (ICCR) of 4.18 and ABE productivity of 0.574 g L−1 h−1, while CCR was alleviated using a cellobiose/xylose mixture with 1.60 and 1.09 g L−1 h−1, respectively. Continuous fermentation with high cell density by cell recycling improved ABE productivity to 5.32 g L−1 h−1 at a dilution rate of 0.686 h−1 owing to high xylose consumption. Further optimization of mixed sugar concentration in the feeding medium induced the best performance of continuous ABE production from mixed sugar without CCR, relative to previous studies: ABE productivity, 6.09 g L−1 h−1; ABE yield, 0.214 g g−1; ICCR, 1.48.

A Study on the Role of Clostridium Saccharoperbutylacetonicum N1-4 (ATCC 13564) in Producing Fermentative Hydrogen

Abstract Comparing with other biological processes, a technological method associated with bio-energy has been developed as the result of the high possibility of fermentative hydrogen productivity; In addition, restricted fossil fuel has been also substituted. The production of fermentative hydrogen is a complicated process influenced by different factors including different kinds of micro-organisms, initial concentration of substrate, inoculum size, initial pH of the medium, concentration of nutrients metals, etc. Thus, the present study is aiming at detecting such different agents to obtain the highest yield of hydrogen and progressing its operation through improving the efficiency of these agents by reliable experimental design. Clostridium saccharoperbutylacetonicum N1-4(ATCC 13564) was applied to produce hydrogen in a batch manner. The highest yield of hydrogen has been resulted in 3.016 mol of hydrogen per mol glucose with production rate of 3.281 mole of hydrogen per hour at 37 °C, 10 % of inoculums size, 10 g/L of an initial glucose concentration, initial pH of medium of 6.5, 30 mg/L of FeSO4.7H2O. Furthermore, the experimental results were compared to kinetic model of Gompertz. Moreover, it was found out that the experimental issues were compatible with this kinetic model with the regression coefficient values of 0.989.

CRISPR-Cas, a highly effective tool for genome editing in Clostridium saccharoperbutylacetonicum N1-4(HMT).

ABSTRACTThe solventogenic clostridia have long been known for their ability to convert sugars from complex feedstocks into commercially important solvents. Although the acetone-butanol-ethanol process fell out of favour decades ago, renewed interest in sustainability and ‘green’ chemistry has re-established our appetite for reviving technologies such as these, albeit with 21st century improvements. As CRISPR-Cas genome editing tools are being developed and applied to the solventogenic clostridia, their industrial potential is growing. Through integration of new pathways, the beneficial traits and historical track record of clostridial fermentation can be exploited to generate a much wider range of industrially relevant products. Here we show the application of genome editing using the endogenous CRISPR-Cas mechanism of Clostridium saccharoperbutylacetonicum N1-4(HMT), to generate a deletion, SNP and to integrate new DNA into the genome. These technological advancements pave the way for application of clostridial species to the production of an array of products.

Enhancement of acid re-assimilation and biosolvent production in Clostridium saccharoperbutylacetonicum through metabolic engineering for efficient biofuel production from lignocellulosic biomass

In the clostridial acetone-butanol-ethanol (ABE) fermentation, the intermediate acetate and butyrate are re-assimilated for solvent production. Here, key genes in ABE pathways in Clostridium saccharoperbutylacetonicum N1-4 were overexpressed to enhance acid re-assimilation and solvent production. With the overexpression of sol operon, acid re-assimilation was enhanced, and ABE production was increased by 20%, with ethanol production increased by six times but almost no increase in butanol production. To further drive carbon flux for C4 metabolites and ultimate butanol production, key genes including hbd, thl, crt and bcd in butanol production pathway were further overexpressed. Compared to the control, butanol, acetone and total ABE production in the new strain was increased by 8%, 18%, and 12.4%, respectively. Finally, simultaneous saccharification and fermentation was carried out using acetate-pretreated switchgrass. 15.4 g/L total ABE (with a yield of 0.31 g/g) was produced in both engineered strains, which was significantly higher than the control.

Towards comprehensive lignocellulosic biomass utilization for bioenergy production: Efficient biobutanol production from acetic acid pretreated switchgrass with Clostridium saccharoperbutylacetonicum N1-4

For bioenergy production from lignocellulosic biomass, most biomass pretreatment processes need to use some chemical reagent as the catalyst to overcome the biomass recalcitrance barrier. Such reagents are usually severe inhibitors for the subsequent microbial fermentation process. Therefore, in many cases, the liquid prehydrolysates fraction (LPF) is discarded after the pretreatment, which is a tremendous waste of materials and leads to additional pollution. Biobutanol produced from the acetone, butanol and ethanol (ABE) fermentation process has been of great interests recently due to its high value as a bioenergy source or biochemical. During ABE fermentation, acetic acid (AA) is produced and then re-assimilated as a carbon source. Thus, AA is a substrate rather than an inhibitor for biobutanol production. In this study, we employed AA as the chemical catalyst for the pretreatment of switchgrass which then be used for ABE production through simultaneous saccharification and fermentation (SSF) with hyper-butanol producing Clostridium saccharoperbutylacetonicum N1-4. Through systematic investigation of the pretreatment conditions and fermentation, we concluded that the optimized condition for switchgrass pretreatment was with 3 g/L AA at 170 °C for 20 min. Both LPF and solid cellulosic fraction (SCF) of the pretreated biomass were highly fermentable. In the fermentation with the SCF/LPF mixture as the substrate, 8.6 g/L butanol (corresponding to a yield of 0.16 g/g) was obtained. Overall, here we demonstrated an innovative and tailored biomass pretreatment strategy for comprehensive and efficient carbon source utilization for bioenergy production.

Curing the endogenous megaplasmid in Clostridium saccharoperbutylacetonicum N1-4 (HMT) using CRISPR-Cas9 and preliminary investigation of the role of the plasmid for the strain metabolism

Clostridium saccharoperbutylacetonicum N1-4 (HMT) is known as a hyper acetone-butanol-ethanol (ABE) producing strain. Within its genome, there is an endogenous megaplasmid (Csp_135p) of 136 kb, which contains 104 protein-encoding genes and two pseudogenes. Till now, the function of the megaplasmid is unknown; meanwhile the existence of the megaplasmid could cause instability for the strain performance and barrier for efficient genome engineering. In order to investigate the function of the megaplasmid as related to ABE fermentation and other metabolisms, here we successfully eliminated the megaplasmid using the CRISPR-Cas9 system, generating the plasmid-null strain N1-4-C. Results from systematic characterization experiments indicated that the N1-4-C strain exhibited higher plasmid transformation efficiency and better plasmid stability than the N1-4 (HMT) strain. In addition, the N1-4-C strain could produce slightly higher concentration of butanol and ABE, along with more efficient re-assimilation of acids. Since there is a gene encoding a lipase on Csp_135p, we evaluated the capability for ester production of both N1-4-C and N1-4 (HMT) strains. Results demonstrated that the Csp_135p plasmid also contributed to the ester production (such as butyl acetate and butyl butyrate; this is the first report for ester production in C. saccharoperbutylacetonicum). This study demonstrated that the CRISPR-Cas9 system can be used as an efficient tool for the curing of endogenous plasmids. The plasmid-null N1-4-C strain can serve as a great platform for the development of more robust strains for biofuel and biochemical production.

Construction of a cell-free synthetic pathway for the production of lactic acid from spent coffee grounds

This study aimed to establish a mathematical modeling to evaluate the inhibitory effect of phenolic derivatives on acetone-butanol-ethanol (ABE) fermentation by Clostridium saccharoperbutylacetonicum N1-4. Vanillin, 4-hydroxybenzoic acid, and syringaldehyde were selected to represent guaiacyl, hydroxyphenyl, and syringyl phenols, respectively, to be examined in a series of fed-batch experiments. Results show the presence of phenolic derivatives blocked the pathway of the assimilation of organic acids and reduced cell growth and glucose utilization. The inhibition model projected that the levels of 0.13, 0.14, and 0.04 g L−1 for vanillin, 4-hydroxybenzoic acid, and syringaldehyde, respectively, resulted in 25% inhibition of butanol production, whereas 100% inhibition was predicted at the levels of 4.94, 4.37, and 4.20 g L−1 for vanillin, 4-hydroxybenzoic acid, and syringaldehyde, respectively. Syringaldehyde was more toxic than the other two compounds. The established model described that the phenolic compounds derived from different phenyl propane monomers of lignin severely obstructed biobutanol production.

Enhancement of sucrose metabolism in Clostridium saccharoperbutylacetonicum N1-4 through metabolic engineering for improved acetone–butanol–ethanol (ABE) fermentation

This work investigated sucrose metabolism in C. saccharoperbutylacetonicum. Inactivation of sucrose catabolism operon resulted in 28.9% decrease in sucrose consumption and 44.1% decrease in ABE production with sucrose as sole carbon source. Interestingly, a large amount of colloid-like polysaccharides were generated in the mutant, which might be due to inefficient intracellular sucrose metabolism. Deletion of transcriptional repressor gene successfully alleviated CCR and enhanced ABE production by 24.7%. Additional overexpression of endogenous sucrose pathway further elevated sucrose consumption and enhanced ABE production by 17.2%, 45.7%, or 22.5% compared to wild type with sucrose, mixed sugars or sugarcane juice as substrate, respectively. The engineered strain could be a robust platform for efficient biofuel production from inexpensive sucrose-based carbon sources.