Efficient butanol production under aerobic conditions by coculture of Clostridium acetobutylicum and Nesterenkonia sp. strain F

Clostridium acetobutylicum is widely used for the microbial production of butanol in a process known as acetone–butanol–ethanol (ABE) fermentation. However, this process suffers from several disadvantages including high oxygen sensitivity of the bacterium which makes the process complicated and necessitate oxygen elimination in the culture medium. Nesterenkonia sp. strain F has attracted interests as the only known non-Clostridia microorganism with inherent capability of butanol production even in the presence of oxygen. This bacterium is not delimited by oxygen sensitivity, a challenge in butanol biosynthesis, but the butanol titer was far below Clostridia. In this study, Nesterenkonia sp. strain F was cocultivated with C. acetobutylicum to form a powerful “coculture” for butanol production thereby eliminating the need for oxygen removal before fermentation. The response surface method was used for obtaining optimal inoculation amount/time and media formulation. The highest yield, 0.31 g/g ABE (13.6 g/L butanol), was obtained by a coculture initiated with 1.5 mg/L Nesterenkonia sp. strain F and inoculated with 15 mg/L C. acetobutylicum after 1.5 hr in a medium containing 67 g/L glucose, 2.2 g/L yeast extract, 4 g/L peptone, and 1.4% (vol/vol) P2 solution. After butanol toxicity assessment, where Nesterenkonia sp. strain F showed no butanol toxicity, the coculture was implemented in a 2 L fermenter with continual aeration leading to 20 g/L ABE.     

Improvements of metabolites tolerance in <Emphasis Type="Italic">Clostridium acetobutylicum</Emphasis> by micronutrient zinc supplementation

Micronutrient zinc is of great importance for acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum. The effect of zinc supplementation on toxic metabolites (formic, acetic, butyric acid and butanol) tolerance during ABE fermentation was investigated under various stress-shock conditions without pH control. Great improvements on cell growth, glucose utilization and butanol production were achieved. In the presence of 0.45 g/L formic acid, zinc contributed to 11.28 g/L butanol produced from 55.24 g/L glucose compared to only 5.27 g/L butanol from 29.49 g/L glucose in the control without zinc supplementation. More importantly, relatively higher levels of 7.5 g/L acetic acid, 5.5 g/L butyric acid and 18 g/L butanol could be tolerated by C. acetobutylicum with zinc supplementation while no fermentation was observed under the same stress-shock condition respectively, suggesting that the acids and butanol tolerance in C. acetobutylicum could be significantly facilitated by pleiotropic regulation of micronutrient zinc. Thus, this paper provides an efficient bioprocess engineering strategy for improving stress tolerance in Clostridium species.     

Enhanced butanol production in Clostridium acetobutylicum ATCC 824 by double overexpression of 6-phosphofructokinase and pyruvate kinase genes

This study elucidated the importance of two critical enzymes in the regulation of butanol production in Clostridium acetobutylicum ATCC 824. Overexpression of both the 6-phosphofructokinase (pfkA) and pyruvate kinase (pykA) genes increased intracellular concentrations of ATP and NADH and also resistance to butanol toxicity. Marked increases of butanol and ethanol production, but not acetone, were also observed in batch fermentation. The butanol and ethanol concentrations were 29.4 and 85.5 % higher, respectively, in the fermentation by double-overexpressed C. acetobutylicum ATCC 824/pfkA+pykA than the wild-type strain. Furthermore, when fed-batch fermentation using glucose was carried out, the butanol and total solvent (acetone, butanol, and ethanol) concentrations reached as high as 19.12 and 28.02 g/L, respectively. The reason for improved butanol formation was attributed to the enhanced NADH and ATP concentrations and increased tolerance to butanol in the double-overexpressed strain.     

Production of butanol from glucose and xylose with immobilized cells of Clostridium acetobutylicum

Pretreated cotton towels were used as carriers to immobilize Clostridium acetobutylicum CGMCC 5234 cells for butanol or ABE production from glucose and xylose. Results showed that cell immobilization was a promising method to increase butanol concentration, yield and productivity regardless of the sugar sources compared with cell suspension. In this study, a high butanol concentration of 10.02 g/L with a yield of 0.20 g/g was obtained from 60 g/L xylose with 9.9 g/L residual xylose using immobilized cells compared with 8.48 g/L butanol and a yield of 0.141 g/g with 20.2 g/L residual xylose from 60 g/L xylose using suspended cells. In mixed-sugar fermentation (30 g/L glucose plus 30 g/L xylose), the immobilized cultures produced 11.1 g/L butanol with a yield of 0.190 g/g, which were 28.3% higher than with suspended cells (8.65 g/L) during which 30 g/L glucose was utilized completely using both immobilized and suspended cells while 3.46 and 13.1 g/L xylose maintained untilized for immobilized and suspended cells, respectively. Based on the results, we speculated that immobilized cells showed enhanced tolerance to butanol toxicity and the cultures preferred glucose to xylose during ABE fermentation. Moreover, the cultures showed obvious difference when grown between high initial concentrations of glucose and those of xylose. Repeated-batch fermentations from glucose with immobilized cells showed better long-term stability than from xylose. At last, the morphologies of free and immobilized cells adsorbed on pretreated cotton towels during the growth cycle were examined by SEM.     

Characterization and evaluation of corn steep liquid in acetone-butanol-ethanol production by Clostridium acetobutylicum

Corn steep liquor (CSL) obtained from a commercial starch manufacturing process was analyzed and tested as a complex nutrient source for ABE (acetone, butanol, and ethanol) production by Clostridium acetobutylicum PJC4BK_AdhE1. CSL contained a wealth of trace elements and nitrogenous components, proteins and amino acids. ABE production increased the content of CSL was raised up to 6% (v/v) in medium and then decreased at higher contents. In 6% CSL-containing medium, C. acetobutylicum PJC4BK_AdhE1 produced 21.4 g/L of ABE with a yield of 0.41 g/g in 18 h of fermentation. Although the final titer of ABE was similar in CSL containing media and Clostridial Growth Medium (CGM, containing yeast extract and asparagines as complex nutrients), the yield and productivity of ABE in 6% CSL-containing medium were found to be higher than 32 and 26%, respectively.     

Enhanced butanol production by optimization of medium parameters using Clostridium acetobutylicum YM1

A new isolate of the solvent-producing Clostridium acetobutylicum YM1 was used to produce butanol in batch culture fermentation. The effects of glucose concentration, butyric acid addition and C/N ratio were studied conventionally (one-factor-at-a-time). Moreover, the interactions between glucose concentration, butyric acid addition and C/N ratio were further investigated to optimize butanol production using response surface methodology (RSM). A central composite design was applied, and a polynomial regression model with a quadratic term was used to analyze the experimental data using analysis of variance (ANOVA). ANOVA revealed that the model was highly significant (p < 0.0001) and the effects of the glucose and butyric acid concentrations on butanol production were significant. The model validation experiment showed 13.82 g/L butanol was produced under optimum conditions. Scale up fermentation in optimized medium resulted in 17 g/L of butanol and 21.71 g/L of ABE. The experimental data of scale up in 5 L bioreactor and flask scale were fitted to kinetic mathematical models published in the literature to estimate the kinetic parameters of the fermentation. The models used gave the best fit for butanol production, biomass and glucose consumption for both flask scale and bioreactor scale up.     

The bioconversion of wood hydrolyzates to butanol and butanediol

Steam-exploded aspenwood chips were acid hydrolysed to their component sugars. Near theoretical solvent yields were achieved in both the acetone-butanol-ethanol (ABE) fermentation and 2,3-butanediol fermentation of these liberated sugars. When Clostridium acetobutylicum was grown on wood hydrolysates, final butanol yields of 9.0 g/L (0.26 g of butanol per g of sugar consumed) were obtained. When Klebsiella pneumoniae was grown on the wood hydrolysates, final butanediol concentrations exceeded 20 g/L, resulting in a bioconversion efficiency approaching 0.5 g of butanediol per g of sugar utilised.     

Comparative analysis of high butanol tolerance and production in clostridia

2016, was the 100 years anniversary from launching of the first industrial acetone-butanol-ethanol (ABE) microbial production process. Despite this long period and also revival of scientific interest in this fermentative process over the last 20 years, solventogenic clostridia, mainly Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium saccharoperbutylacetonicum and Clostridium pasteurianum, still have most of their secrets. One such poorly understood mechanism is butanol tolerance, which seems to be one of the most significant bottlenecks obstructing industrial exploitation of the process because the maximum achievable butanol concentration is only about 21 g/L. This review describes all the known cellular responses elicited by butanol, such as modifications of cell membrane and cell wall, formation of stress proteins, extrusion of butanol by efflux pumps, response of regulatory pathways, and also maps both random and targeted mutations resulting in high butanol production phenotypes. As progress in the field is inseparably associated with emerging methods, enabling a deeper understanding of butanol tolerance and production, progress in these methods, including genome mining, RNA sequencing and constructing of genome scale models are also reviewed. In conclusion, a comparative analysis of both phenomena is presented and a theoretical relationship is described between butanol tolerance/high production and common features including efflux pump formation/activity, stress protein production, membrane modifications and biofilm growth.     

Enhancing Butanol Production under the Stress Environments of Co-Culturing Clostridium acetobutylicum/Saccharomyces cerevisiae Integrated with Exogenous Butyrate Addition

In this study, an efficient acetone-butanol-ethanol (ABE) fermentation strategy integrating Clostridium acetobutylicum/Saccharomyces cerevisiae co-culturing system with exogenous butyrate addition, was proposed and experimentally conducted. In solventogenic phase, by adding 0.2 g-DCW/L-broth viable S. cerevisiae cells and 4.0 g/L-broth concentrated butyrate solution into C. acetobutylicum culture broth, final butanol concentration and butanol/acetone ratio in a 7 L anaerobic fermentor reached the highest levels of 15.74 g/L and 2.83 respectively, with the increments of 35% and 43% as compared with those of control. Theoretical and experimental analysis revealed that, the proposed strategy could, 1) extensively induce secretion of amino acids particularly lysine, which are favorable for both C. acetobutylicum survival and butanol synthesis under high butanol concentration environment; 2) enhance the utilization ability of C. acetobutylicum on glucose and over-produce intracellular NADH for butanol synthesis in C. acetobutylicum metabolism simultaneously; 3) direct most of extra consumed glucose into butanol synthesis route. The synergetic actions of effective amino acids assimilation, high rates of substrate consumption and NADH regeneration yielded highest butanol concentration and butanol ratio in C. acetobutylicum under this stress environment. The proposed method supplies an alternative way to improve ABE fermentation performance by traditional fermentation technology.     

高抗逆高丁比拜氏梭菌的选育及其性能考察简

以抗逆突变株Clostridium beijerinckii IB4为出发菌株,通过常压室温等离子体诱变（ ARTP ）,刃天青平板初筛,摇瓶发酵复筛,筛选出1株高抗逆高丁比的突变菌株C.beijerinckii IT111。发酵结果表明：该突变菌株利用多种C源时均展现其高丁醇比的特性,以玉米芯酸解糖液为C源时,溶剂产量达到10.5 g/L,丁醇8.0 g/L,丁醇比高达76％。抑制物抗逆性测试结果显示：糠醛和酸类对C.beijerinckii发酵影响较小,酚类物质对C.beijerinckii抑制作用较强,其中以香草醛为最。综上所述,C.beijerinckii IT111是1株极具潜力的利用木质纤维原料制备丁醇的菌株。     

Utilisation of saccharides in extruded domestic organic waste by Clostridium acetobutylicum ATCC 824 for production of acetone, butanol and ethanol

Domestic organic waste (DOW) collected in The Netherlands was analysed and used as substrate for acetone, butanol and ethanol (ABE) production. Two different samples of DOW, referred to as fresh DOW and dried DOW, were treated by extrusion in order to expand the polymer fibres present and to obtain a homogeneous mixture. The extruded material was analysed with respect to solvent and hot water extractives, uronic acids, lignin, sugars and ash. The total sugar content in the polymeric fractions of the materials varied from 27.7% to 39.3% (w/w), in which glucose represented the 18.4 and 25.1% of the materials, for fresh and dried DOW, respectively. The extruded fresh DOW was used as substrate for the ABE fermentation by the solventogenic strain Clostridium acetobutylicum ATCC 824. This strain was grown on a suspension of 10% (w/v) DOW in demineralised water without further nutrient supplement. This strain produced 4 g ABE/100 g extruded DOW. When C. acetobutylicum ATCC 824 was grown on a suspension of 10% (w/v) DOW hydrolysed by a combination of commercial cellulases and β-glucosidases, the yield of solvents increased to 7.5 g ABE/100 g extruded DOW. The utilisation of sugar polymers in both hydrolysed and non-hydrolysed DOW was determined, showing that only a small proportion of the polymers had been consumed by the bacteria. These results indicate that growth and ABE production on DOW is mainly supported by soluble saccharides in the medium. Received: 5 November 1999 / Received revision: 21 February 2000 / Accepted: 25 February 2000     

High-titer n-butanol production by clostridium acetobutylicum JB200 in fed-batch fermentation with intermittent gas stripping

Acetone–butanol–ethanol (ABE) fermentation with a hyper‐butanol producing Clostridium acetobutylicum JB200 was studied for its potential to produce a high titer of butanol that can be readily recovered with gas stripping. In batch fermentation without gas stripping, a final butanol concentration of 19.1 g/L was produced from 86.4 g/L glucose consumed in 78 h, and butanol productivity and yield were 0.24 g/L h and 0.21 g/g, respectively. In contrast, when gas stripping was applied intermittently in fed‐batch fermentation, 172 g/L ABE (113.3 g/L butanol, 49.2 g/L acetone, 9.7 g/L ethanol) were produced from 474.9 g/L glucose in six feeding cycles over 326 h. The overall productivity and yield were 0.53 g/L h and 0.36 g/g for ABE and 0.35 g/L h and 0.24 g/g for butanol, respectively. The higher productivity was attributed to the reduced butanol concentration in the fermentation broth by gas stripping that alleviated butanol inhibition, whereas the increased butanol yield could be attributed to the reduced acids accumulation as most acids produced in acidogenesis were reassimilated by cells for ABE production. The intermittent gas stripping produced a highly concentrated condensate containing 195.9 g/L ABE or 150.5 g/L butanol that far exceeded butanol solubility in water. After liquid–liquid demixing or phase separation, a final product containing ～610 g/L butanol, ～40 g/L acetone, ～10 g/L ethanol, and no acids was obtained. Compared to conventional ABE fermentation, the fed‐batch fermentation with intermittent gas stripping has the potential to reduce at least 90% of energy consumption and water usage in n‐butanol production from glucose. Biotechnol. Bioeng. 2012; 109: 2746–2756. © 2012 Wiley Periodicals, Inc.     

Ex situ product recovery for enhanced butanol production by <Emphasis Type="Italic">Clostridium beijerinckii</Emphasis>

In situ butanol recovery fermentation has been intensively studied as an effective alternative to conventional butanol production, which is limited due to the cellular toxicity of butanol. However, the low biocompatibility of adsorbents often leads to failure of in situ recovery fermentations. In this study, Clostridium beijerinckii NCIMB 8052 was cultured in flasks without shaking and in situ recovery fermentation was performed by using an adsorbent L493. The amounts of acetone, butanol, and ethanol (ABE) increased by 34.4 % in the presence of the adsorbent. In contrast, cell growth and production of organic acids and ABE were retarded in the 7-L batch fermentations with in situ butanol recovery. Cell damage occurred in the fermentor upon agitation in the presence of the adsorbent, unlike in static flask cultures with in situ recovery. Ex situ recovery fermentation using circulation of fermentation broth after mid-exponential phase of cell growth was developed to avoid adsorbent-cell incompatibility. No apparent cell damage was observed and 25.7 g/L of ABE was produced from 86.2 g/L glucose in the fed-batch mode using 7 L fermentors. Thus, ex situ recovery fermentation with C. beijerinckii is effective for enhancing butanol fermentation.     

Acetone–butanol–ethanol production with high productivity using Clostridium acetobutylicum BKM19

Conventional acetone–butanol–ethanol (ABE) fermentation is severely limited by low solvent titer and productivities. Thus, this study aims at developing an improved Clostridium acetobutylicum strain possessing enhanced ABE production capability followed by process optimization for high ABE productivity. Random mutagenesis of C. acetobutylicum PJC4BK was performed by screening cells on fluoroacetate plates to isolate a mutant strain, BKM19, which exhibited the total solvent production capability 30.5% higher than the parent strain. The BKM19 produced 32.5 g L^?1 of ABE (17.6 g L^?1 butanol, 10.5 g L^?1 ethanol, and 4.4 g L^?1 acetone) from 85.2 g L^?1 glucose in batch fermentation. A high cell density continuous ABE fermentation of the BKM19 in membrane cell‐recycle bioreactor was studied and optimized for improved solvent volumetric productivity. Different dilution rates were examined to find the optimal condition giving highest butanol and ABE productivities. The maximum butanol and ABE productivities of 9.6 and 20.0 g L^?1 h^?1, respectively, could be achieved at the dilution rate of 0.85 h^?1. Further cell recycling experiments were carried out with controlled cell‐bleeding at two different bleeding rates. The maximum solvent productivities were obtained when the fermenter was operated at a dilution rate of 0.86 h^?1 with the bleeding rate of 0.04 h^?1. Under the optimal operational condition, butanol and ABE could be produced with the volumetric productivities of 10.7 and 21.1 g L^?1 h^?1, and the yields of 0.17 and 0.34 g g^?1, respectively. The obtained butanol and ABE volumetric productivities are the highest reported productivities obtained from all known‐processes. Biotechnol. Bioeng. 2013; 110: 1646–1653. © 2013 Wiley Periodicals, Inc.     

Metabolic engineering of Clostridium acetobutylicum for the enhanced production of isopropanol‐butanol‐ethanol fuel mixture

Butanol is considered as a superior biofuel, which is conventionally produced by clostridial acetone‐butanol‐ethanol (ABE) fermentation. Among ABE, only butanol and ethanol can be used as fuel alternatives. Coproduction of acetone thus causes lower yield of fuel alcohols. Thus, this study aimed at developing an improved Clostridium acetobutylicum strain possessing enhanced fuel alcohol production capability. For this, we previously developed a hyper ABE producing BKM19 strain was further engineered to convert acetone into isopropanol. The BKM19 strain was transformed with the plasmid pIPA100 containing the sadh (primary/secondary alcohol dehydrogenase) and hydG (putative electron transfer protein) genes from the Clostridium beijerinckii NRRL B593 cloned under the control of the thiolase promoter. The resulting BKM19 (pIPA100) strain produced 27.9 g/l isopropanol‐butanol‐ethanol (IBE) as a fuel alcohols with negligible amount of acetone (0.4 g/l) from 97.8 g/l glucose in lab‐scale (2 l) batch fermentation. Thus, this metabolically engineered strain was able to produce 99% of total solvent produced as fuel alcohols. The scalability and stability of BKM19 (pIPA100) were evaluated at 200 l pilot‐scale fermentation, which showed that the fuel alcohol yield could be improved to 0.37 g/g as compared to 0.29 g/g obtained at lab‐scale fermentation, while attaining a similar titer. To the best of our knowledge, this is the highest titer of IBE achieved and the first report on the large scale fermentation of C. acetobutylicum for IBE production. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1083–1088, 2013     

Enhancement of ABE fermentation through regulation of ammonium acetate and D–xylose uptake from acid-pretreated corncobs

Clostridium acetobutylicum TISTR 1462 and Clostridium beijerinckii TISTR 1461 were chosen to optimize acetone–butanol–ethanol (ABE) fermentation by using glucose as a carbon source. The enhancement in its productivity by adding various concentrations of ammonium acetate was studied. Then, the variation of glucose/xylose ratios in the pre-grown medium was investigated. The results showed that both increased ammonium acetate in the production medium and D–xylose in the pre-grown medium could produce more ABE. With these conditions, using corncob hydrolysate as a substrate, 20.58 g/L ABE was produced from C. beijerinckii TISTR 1461 with 0.44 g/L/h and 0.45 of ABE productivity and yield, respectively.     

ABE production from yellow poplar through alkaline pre-hydrolysis, enzymatic saccharification, and fermentation

ABE (acetone-butanol-ethanol) was produced through alkaline pre-hydrolysis, enzymatic saccharification, and fermentation using yellow poplar as a raw material. In alkaline pre-hydrolysis, 51.1% of the biomass remained as a residue. In the main woody components, the degrees of lignin and xylan removal were 94.3 and 62.0%, respectively. A yield of 80.9% for cellulose-to-glucose and 81.2% for xylan-to-xylose were obtained by enzymatic hydrolysis. The sugar composition of enzymatic hydrolysate was 95.1 g/L of glucose and 21.4 g/L of xylose. The enzymatic hydrolysate also contained 0.5 g/L of acetic acid and 0.5 g/L of total phenolics. Furfural and 5-hydroxymethylfurfural (5-HMF) were not detected in this hydrolysate. The yellow poplar hydrolysate (YPH) from enzymatic saccharification was used for the production of ABE using Clostridium acetobutylicum and C. beijerinckii. In YPH fermentation, C. acetobutylicum produced 18.1 g/L total ABE (productivity 0.38 g/L h, and yield 0.42), and C. beijerinckii produced 12.1 g/L (productivity 0.25 g/L h, and yield 0.37). Although the ABE productivity by C. beijerinckii was slightly low, the general performance of ABE fermentation in YPH was similar to or higher than those reported previously. Therefore, alkaline pre-hydrolysis could be a very effective pretreatment step prior to enzymatic hydrolysis.     

Engineering Clostridium acetobutylicum for production of kerosene and diesel blendstock precursors

Processes for the biotechnological production of kerosene and diesel blendstocks are often economically unattractive due to low yields and product titers. Recently, Clostridium acetobutylicum fermentation products acetone, butanol, and ethanol (ABE) were shown to serve as precursors for catalytic upgrading to higher chain-length molecules that can be used as fuel substitutes. To produce suitable kerosene and diesel blendstocks, the butanol:acetone ratio of fermentation products needs to be increased to 2–2.5:1, while ethanol production is minimized. Here we show that the overexpression of selected proteins changes the ratio of ABE products relative to the wild type ATCC 824 strain. Overexpression of the native alcohol/aldehyde dehydrogenase (AAD) has been reported to primarily increase ethanol formation in C. acetobutylicum. We found that overexpression of the AAD^D485G variant increased ethanol titers by 294%. Catalytic upgrading of the 824(aad^D485G) ABE products resulted in a blend with nearly 50 wt%≤C₉ products, which are unsuitable for diesel. To selectively increase butanol production, C. beijerinckii aldehyde dehydrogenase and C. ljungdhalii butanol dehydrogenase were co-expressed (strain designate 824(Cb ald-Cl bdh)), which increased butanol titers by 27% to 16.9 g L⁻¹ while acetone and ethanol titers remained essentially unaffected. The solvent ratio from 824(Cb ald-Cl bdh) resulted in more than 80 wt% of catalysis products having a carbon chain length≥C₁₁ which amounts to 9.8 g L⁻¹ of products suitable as kerosene or diesel blendstock based on fermentation volume. To further increase solvent production, we investigated expression of both native and heterologous chaperones in C. acetobutylicum. Expression of a heat shock protein (HSP33) from Bacillus psychrosaccharolyticus increased the total solvent titer by 22%. Co-expression of HSP33 and aldehyde/butanol dehydrogenases further increased ABE formation as well as acetone and butanol yields. HSP33 was identified as the first heterologous chaperone that significantly increases solvent titers above wild type C. acetobutylicum levels, which can be combined with metabolic engineering to further increase solvent production.     

Combining chemical flocculation and bacterial co-culture of Cupriavidus taiwanensis and Ureibacillus thermosphaericus to detoxify a hardwood hemicelluloses hydrolysate and enable acetone–butanol–ethanol fermentation leading to butanol

Butanol, a fuel with better characteristics than ethanol, can be produced via acetone–butanol–ethanol (ABE) fermentation using lignocellulosic biomass as a carbon source. However, many inhibitors present in the hydrolysate limit the yield of the fermentation process. In this work, a detoxification technology combining flocculation and biodetoxification within a bacterial co-culture composed of Ureibacillus thermosphaericus and Cupriavidus taiwanensis is presented for the first time. Co-culture-based strategies to detoxify filtered and unfiltered hydrolysates have been investigated. The best results of detoxification were obtained for a two-step approach combining flocculation to biodetoxification. This sequential process led to a final phenolic compounds concentration of 1.4 g/L, a value close to the minimum inhibitory level observed for flocculated hydrolysate (1.1 g/L). The generated hydrolysate was then fermented with Clostridium acetobutylicum ATCC 824 for 120 h. A final butanol production of 8 g/L was obtained, although the detoxified hydrolysate was diluted to reach 0.3 g/L of phenolics to ensure noninhibitory conditions. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2753, 2019.     

Promotion of the Clostridium acetobutylicum ATCC 824 growth and acetone–butanol–ethanol fermentation by flavonoids

An unexpected promotion effect of Ginkgo leaf on the growth of Clostridium acetobutylicum ATCC 824 and acetone–butanol–ethanol (ABE) fermentation was investigated. Component analysis of Ginkgo leaf was carried out and flavonoids were determined as the potential key metabolites. Then the flavonoids feeding experiments were carried out. Results showed that addition of only 10 mg/L flavonoids to the fermentation broth can promote butanol and ABE titre up to 14.5 and 17.8 g/L after 5 days of fermentation, that is, 74 and 68 % higher than the control. A 2.2-fold biomass also has been achieved. Furthermore, by employing such novel founding, we easily exploited flavonoids from soybean and some agriculture wastes as the wide-distributed and economic feasible ABE fermentation promoter. The mechanism of the above effects was investigated from the perspective of oxidation–reduction potential. This work opens a new way in the efforts to increase the titer of butanol.