Biotransformation of furfural and 5-hydroxymethyl furfural by enteric bacteria

Summary A survey was conducted with seventeen enteric bacterial strains (including the generaKlebsiella, Enterobacter, Escherichia, Citrobacter, Edwardsiella andProteus) to examine their ability to transform furfural and 5-hydroxymethyl furfural (5-MHF). The enteric bacteria were able to convert furfural to furfuryl alcohol under both aerobic and anaerobic conditions in a relatively short incubation time of 8 h. 5-HMF was transformed by all the enteric bacteria studied to an unidentified compound postulated to be 5-hydroxymethyl furfuryl alcohol, which had an absorbance maximum of 222 nm. These bacteria did not transform furfuryl alcohol or 2-furoic acid. The enteric bacteria did not use furfural, 5-HMF, furfuryl alcohol or 2-furoic acid as sole source of carbon and energy. Biotransformation of furfural and 5-HMF was accomplished by co-metabolism in the presence of glucose and peptone as main substrates. The rate of transformation was similar under both aerobic and anaerobic conditions. These transformations are likely to be of value in the detoxification of furfurals, and in their ultimate conversion to methane and CO₂ by anaerobic digestion.     

Hydrolysis of sorghum straw using phosphoric acid: evaluation of furfural production

Sorghum straw is a waste that has been studied scarcely. The main application is its use as raw material for xylose production. Xylose is a hemicellulosic sugar mainly used for its bioconversion toward xylitol. An alternative use could be its conversion toward furfural. The objective of this work was to study the furfural production by hydrolysis of sorghum straw with phosphoric acid at 134 degrees C. Several concentrations of H(3)PO(4) in the range 2-6% and reaction time (range 0-300 min) were evaluated. Kinetic parameters of mathematical models for predicting the concentration of xylose, glucose, arabinose, acetic acid and furfural in the hydrolysates were found. Optimal conditions for furfural production by acid hydrolysis were 6% H(3)PO(4) at 134 degrees C for 300 min, which yielded a solution with 13.7 g furfural/L, 4.0 g xylose/L, 2.9 g glucose/L, 1.1g arabinose/L and 1.2g acetic acid/L. The furfural yield of the process was 0.1336 g furfural/g initial dry matter was obtained. The results confirmed that sorghum straw can be used for furfural production when it is hydrolyzed using phosphoric acid.     

Main and interaction effects of acetic acid, furfural, and p-hydroxybenzoic acid on growth and ethanol productivity of yeasts

The influence of the factors acetic acid, furfural, and p-hydroxybenzoic acid on the ethanol yield (YEtOH) of Saccharomyces cerevisiae, bakers' yeast, S. cerevisiae ATCC 96581, and Candida shehatae NJ 23 was investigated using a 2(3)-full factorial design with 3 centrepoints. The results indicated that acetic acid inhibited the fermentation by C. shehatae NJ 23 markedly more than by bakers' yeast, whereas no significant difference in tolerance towards the compounds was detected between the S. cerevisiae strains. Furfural (2 g L-1) and the lignin derived compound p-hydroxybenzoic acid (2 g L-1) did not affect any of the yeasts at the cell mass concentration used. The results indicated that the linear model was not adequate to describe the experimental data (the p-values of curvatures were 0.048 for NJ 23 and 0.091 for bakers' yeast). Based on the results from the 2(3)-full factorial experiment, an extended experiment was designed based on a central composite design to investigate the influence of the factors on the specific growth rate (mu), biomass yield (Yx), volumetric ethanol productivity (QEtOH), and YEtOH. Bakers' yeast was chosen in the extended experiment due to its better tolerance towards acetic acid, which makes it a more interesting organism for use in industrial fermentations of lignocellulosic hydrolysates. The inoculum size was reduced in the extended experiment to reduce any increase in inhibitor tolerance that might be due to a large cell inoculum. By dividing the experiment in blocks containing fermentations performed with the same inoculum preparation on the same day, much of the anticipated systematic variation between the experiments was separated from the experimental error. The results of the fitted model can be summarised as follows: mu was decreased by furfural (0-3 g L-1). Furfural and acetic acid (0-10 g L-1) also interacted negatively on mu. Furfural concentrations up to 2 g L-1 stimulated Yx in the absence of acetic acid whereas higher concentrations decreased Yx. The two compounds interacted negatively on Yx and YEtOH. Acetic acid concentrations up to 9 g L-1 stimulated QEtOH, whereas furfural (0-3 g L-1) decreased QEtOH. Acetic acid in concentrations up to 10 g L-1 stimulated YEtOH in the absence of furfural, and furfural (0-2 g L-1) slightly increased YEtOH in the absence of acetic acid whereas higher concentrations caused inhibition. Acetic acid and furfural interacted negatively on YEtOH.     

Acidic cesium salts of 12-tungstophosphoric acid as catalysts for the dehydration of xylose into furfural

Cesium salts of 12-tungstophosphoric acid, Cs(x)H(3-x)PW(12)O(40) (Cs(x)PW), in the bulk form or supported on medium-pore MCM-41 (3.7 nm) or large-pore (9.6 nm) micelle-templated silicas are active solid acid catalysts for the cyclodehydration of xylose into furfural, in a toluene/water solvent system (T/W) or in dimethyl sulfoxide (DMSO). The catalytic results are comparable to those obtained using sulfuric acid, under similar reaction conditions. The initial activities increase in the order H(3)PW(12)O(40)相似文献   

Isolation, purification and characterization of histidino-threosidine, a novel Maillard reaction protein crosslink from threose, lysine and histidine

We isolated a novel acid-labile yellow chromophore from the incubation of lysine, histidine and d-threose and identified its chemical structure by one and two-dimensional NMR spectroscopy combined with LC-tandem mass spectrometry. This new cross-link exhibits a UV absorbance maximum at 305 nm and a molecular mass of 451 Da. The proposed structure is 2-amino-5-(3-((4-(2-amino-2-carboxyethyl)-1H-imidazol-1-yl)methyl)-4-(1,2-dihydroxyethyl)-2-formyl-1H-pyrrol-1-yl)pentatonic acid, a cross-link between lysine and histidine with addition of two threose molecules. It was in part deduced and confirmed through synthesis of the analogous compound from n-butylamine, imidazole and d-threose. We assigned the compound the trivial name histidino-threosidine. Systemic incubation revealed that histidino-threosidine can be formed in low amounts from fructose, glyceraldehyde, methylglyoxal, glycolaldehyde, ascorbic acid, and dehydroascorbic acid, but at a much higher yield with degradation products of ascorbic acid, i.e. threose, erythrose, and erythrulose. Bovine lens protein incubated with 10 and 50 mM threose for two weeks yielded 560 and 2840 pmol/mg histidino-threosidine. Histidino-threosidine is to our knowledge the first Maillard reaction product known to involve histidine in a crosslink.     

N6-(1-carboxyethyl)lysine formation by Streptococcus lactis. Purification, synthesis, and stereochemical structure

During growth in an arginine-deficient (chemically defined) medium, cells of Streptococcus lactis K1 formed significant amounts of a previously undetected ninhydrin-positive compound. This intracellular compound did not cochromatograph with any of a wide range of amino acids or amino acid analogs tested. However, by two-dimensional thin layer chromatography, the unknown compound migrated close to the recently discovered N5-(1-carboxyethyl)ornithine (Thompson, J., Curtis, M. A., and Miller, S. P. F. (1986) J. Bacteriol. 167, 522-529; Miller, S. P. F., and Thompson, J. (1987) J. Biol. Chem. 262, 16109-16115). The purified compound behaved as a neutral amino acid and eluted between valine and methionine in the amino acid analyzer. The results of 1H NMR spectroscopy suggested the presence of a lysine backbone and a coupled methyl-methine unit in the molecule, and 13C NMR showed that there were nine carbon atoms, of which two (C-1 and C-7) were carboxyl carbons. The simplest structure compatible with the physicochemical data was that of an alkylated derivative of lysine. The identity of this new amino acid, N6-(1-carboxyethyl)lysine, was confirmed by chemical synthesis. In vivo labeling experiments conducted using L[U-14C]lysine and [epsilon-15N]lysine showed that exogenous lysine served as the precursor of intracellular N6-(1-carboxyethyl)lysine and that the epsilon-amino N atom was conserved during biosynthesis of the lysine derivative. Of the two possible diastereomers (2S,8S or 2S,8R) of N6-(1-carboxyethyl)lysine, comparative 13C NMR spectroscopy established that the amino acid produced by S. lactis K1 was exclusively of the 2S,8S configuration.     

Acid-catalyzed conversion of xylose, xylan and straw into furfural by microwave-assisted reaction

Furfural is a biomass derived-chemical that can be used to replace petrochemicals. In this study, the acid-catalyzed conversion of xylose and xylan to furfural by microwave-assisted reaction was investigated at selected ranges of temperature (140-190 °C), time (1-30 min), substrate concentration (1:5-1:200 solid:liquid ratio), and pH (2-0.13). We found that a temperature of 180 °C, a solid:liquid ratio of 1:200, a residence time of 20 min, and a pH of 1.12 gave the best furfural yields. The effect of different Brønsted acids on the conversion efficiency of xylose and xylan was also evaluated, with hydrochloric acid being found to be the most effective catalyst. The microwave-assisted process provides highly efficient conversion: furfural yields obtained from wheat straw, triticale straw, and flax shives were 48.4%, 45.7%, and 72.1%, respectively.     

Methanogenesis from furfural by defined mixed cultures

Methanogenesis from furfural by defined mixed cultures was studied. Under sulfate-reducing conditions, a Desulfovibrio strain was used as the furfural-degrading species producing acetic acid. This sulfate-reducing bacterium (SRB) Desulfovibrio strain B is an incomplete oxidizer, unable to carry out the terminal oxidation of organic substrates, leaving acetic acid as the end product. Introduction of acetate-utilizing methanogenic archaeon Methanosarcina barkeri 227 converted acetic acid to methane. This well-defined mixed consortium used furfural as its sole source of carbon and converted it to methane and CO₂. In the mixed culture, when a methanogen inhibitor was used in the culture medium, furfural was converted to acetic acid by the Desulfovibrio strain B, but acetic acid did not undergo further metabolism. On the other hand, when the growth of Desulfovibrio in the consortium was suppressed with a specific SRB inhibitor, namely molybdate, furfural was not degraded. Thus, the metabolic activities of both Desulfovibrio strain B and M. barkeri 227 were essential for the complete degradation of furfural. Received: 15 August 2001 / Accepted: 20 September 2001     

Biotransformation of furfural and 5-hydroxymethyl furfural (HMF) by Clostridium acetobutylicum ATCC 824 during butanol fermentation

The ability of fermenting microorganisms to tolerate furan aldehyde inhibitors (furfural and 5-hydroxymethyl furfural (HMF)) will enhance efficient bioconversion of lignocellulosic biomass hydrolysates to fuels and chemicals. The effect of furfural and HMF on butanol production by Clostridium acetobutylicum 824 was investigated. Whereas specific growth rates, μ, of C. acetobutylicum in the presence of furfural and HMF were in the range of 15-85% and 23-78%, respectively, of the uninhibited Control, μ increased by 8-15% and 23-38% following exhaustion of furfural and HMF in the bioreactor. Using high performance liquid chromatography and spectrophotometric assays, batch fermentations revealed that furfural and HMF were converted to furfuryl alcohol and 2,5-bis-hydroxymethylfuran, respectively, with specific conversion rates of 2.13g furfural and 0.50g HMF per g (biomass) per hour, by exponentially growing C. acetobutylicum. Biotransformation of these furans to lesser inhibitory compounds by C. acetobutylicum will probably enhance overall fermentation of lignocellulosic hydrolysates to butanol.     

Removal and recovery of furfural, 5-hydroxymethylfurfural, and acetic acid from aqueous solutions using a soluble polyelectrolyte

In the cellulosic ethanol process, furfural, 5-hydroxymethylfurfural (HMF), and acetic acid are formed during the high temperature acidic pretreatment step needed to convert biomass into fermentable sugars. These compounds can inhibit cellulase enzymes and fermentation organisms at relatively low concentrations (≥ 1 g/L). Effective removal of these inhibitory compounds would allow the use of more severe pretreatment conditions to improve sugar yields and lead to more efficient fermentations; if recovered and purified, they could also be sold as valuable by-products. This study investigated the separation of aldhehydes (furfural and HMF) and organic acid (acetic acid) inhibitory compounds from simple aqueous solutions by using polyethyleneimene (PEI), a soluble cationic polyelectrolyte. PEI added to simple solutions of each inhibitor at a ratio of 1 mol of functional group to 1 mol inhibitor removed up to 89.1, 58.6, and 81.5 wt% of acetic acid, HMF, and furfural, respectively. Furfural and HMF were recovered after removal by washing the polyelectrolyte/inhibitor complex with dilute sulfuric acid solution. Recoveries up to 81.0 and 97.0 wt% were achieved for furfural and HMF, respectively. The interaction between PEI and acetic acid was easily disrupted by the addition of chloride ions, sulfate ions, or hydroxide ions. The use of soluble polymers for the removal and recovery of inhibitory compounds from biomass slurries is a promising approach to enhance the efficiency and economics of an envisioned biorefinery.     

Specificity of the interaction of furfural with DNA

Furfural or 2-furaldehyde is a dietary mutagen and is present in various frequently consumed food products. The alkaline unwinding assay and protection of cleavage sites from the action of various restriction enzymes was used to study the interaction of furfural with DNA. Alkaline unwinding experiments showed the formation of an increasing number of strand breaks in duplex DNA both with increasing furfural concentration and with time of reaction. Treatment of lambda phage DNA with furfural protected cleavage with restriction endonucleases DraI and SspI but not with ApaI, BssHII and SacII. These results indicate that under the conditions used furfural reacts exclusively with AT base pairs. A minimum of 3-4 consecutive AT base pairs are required for this reaction. This was determined by the use of several restriction enzymes whose hexanucleotide recognition sequences contain subsets of AT base pairs.     

Isolation and characterization of a furfural degrading sulfate-reducing bacterium from an anaerobic digester

A sulfate-reducing bacterium (SRB) was isolated from a continuous anaerobic digester, which converted the furfural-containing wastewater to methane and CO₂. This SRB isolate could use furfural, furfuryl alcohol, and 2-furoic acid as sole source of carbon and energy in a defined mineral sulfate medium. Acetic acid was the major end product of furfural degradation. This organism also used wide varieties of other carbon sources, including ethanol, pyruvate, lactate, succinate, propanol, formate, and malate. The SRB isolate contained the electron carrier desulfoviridin. It used SO₄, NO₃, and thiosulfate as electron acceptors. This isolate used ammonium chloride, nitrate and glutamate as nitrogen source. The characteristics of the SRB isolate were closely similar toDesulfovibrio sp.     

乙酸、糠醛和5-羟甲基糠醛对产酸克雷伯氏菌发酵生产2,3-丁二醇的影响

为了解产酸克雷伯氏菌对木质纤维素水解液中主要抑制物的耐受和代谢,考察了产酸克雷伯氏菌发酵生产2,3-丁二醇(2,3-butanediol,2,3-BDO)过程中对3种发酵抑制物乙酸、糠醛和5-羟甲基糠醛(5-hydroxymethylfurfural HMF)的耐受以及抑制物浓度的变化,检测了糠醛和HMF的代谢产物.结果表明:产酸克雷伯氏菌对乙酸、糠醛和HMF的耐受浓度分别为30 g/L、4 g/L和5 g/L.并且部分乙酸可作为生产2,3-丁二醇的底物,在0～30 g/L浓度范围内可提高2,3-丁二醇的产量.发酵过程中产酸克雷伯氏菌可将HMF和糠醛全部转化,其中约70％HMF被转化为2,5-呋喃二甲醇,30％HMF和全部糠醛被菌体代谢.研究表明在木质纤维素水解液生产2,3-丁二醇的脱毒过程中可优先考虑脱除糠醛,一定浓度的乙酸可以不用脱除.     

Fluorometric measurement of furfural and 5-hydroxymethylfurfural

Zine(II) forms highly fluorescent chelates with the aroyl hydrazones of furfural and 5-hydroxymethylfurfural, with the latter being more fluorescent than the former. The choice of aromatic acid hydrazide (aroyl hydrazine) as analytical reagents for furfurals was examined; 4-toluenesulfonic acid hydrazine was the most sensitive reagent examined, giving a uv fluorescence 10 times as sensitive as 4-hydroxygenzoic acid hydrazide (PAHBAH). More convenient visible fluorescence was given by PAHBAH and related compounds, and these are capable of detecting less than 500 pmol 5-hydroxymethylfurfural. The condensation reaction is complete in 30 mm ethanolic hydrochloric acid within 2 min at 60°C, and the stable product forms the fluorescent chelate on mixing with a zinc-diethanolamine solution in ethanol.     

Properties of chlorogenic acid quinone: relationship between browning and the formation of hydrogen peroxide from a quinone solution

Chlorogenic acid is the major polyphenol in foods derived from plants and is a good substrate for polyphenol oxidase. Chlorogenic acid quinone (CQA-Q), which is an oxidative product of chlorogenic acid by polyphenol oxidase, is an important intermediate compound in enzymatic browning. CQA-Q was prepared, and its properties and the relationship with browning were examined. The quinone solution was yellow or orange, and its molecular absorption coefficient was estimated to be 1.7 x 10(3) for 325 nm and 9.7 x 10(2) for 400 nm in an acidic aqueous solution. Chlorogenic acid and H2O2 were spontaneously generated in the CQA-Q solution as the yellowish color of the solution gradually faded. A pale colored polymer was the major product in the reaction solution. Amino acids such as lysine and arginine added to CQA-Q solution did not repress the fading of the yellowish color of the solution. We concluded from these results that CQA-Q itself and a mixture of CQA-Q and amino acids did not form intensive brown pigments in the acidic aqueous solution. H2O2 spontaneously formed in the CQA-Q solution, and other polyphenols might have played an important role in the formation of the brown color by enzymatic browning.     

One-step hydrogenation-esterification of furfural and acetic acid over bifunctional Pd catalysts for bio-oil upgrading

This contribution focuses on one-step hydrogenation-esterification (OHE) of furfural and acetic acid, which are difficult to treat and typically present in crude bio-oil, as a model reaction for bio-oil upgrading. A bifunctional catalyst is needed for OHE reaction. Among tested bifunctional catalysts, the 5%Pd/Al₂(SiO₃)₃ shows the best catalytic performance. Compared to the physical mixture of 5%Pd/C + Al₂(SiO₃)₃, there is a synergistic effect between metal sites and acid sites over 5%Pd/Al₂(SiO₃)₃ for the OHE reaction. A moderate reaction condition would be required to obtain high yields of alcohol and ester along with lower byproduct yields. In this work, the optimum selectivity to desired products (alcohol and ester) of 66.4% is obtained, where the conversion of furfural is 56.9%. Other components, typically present in bio-oils, have little effects on the OHE of FAL and HAc. This OHE method is a promising route for efficient upgrading of bio-oil.     

Detoxification of furfural in Corynebacterium glutamicum under aerobic and anaerobic conditions

The toxic fermentation inhibitors in lignocellulosic hydrolysates raise serious problems for the microbial production of fuels and chemicals. Furfural is considered to be one of the most toxic compounds among these inhibitors. Here, we describe the detoxification of furfural in Corynebacterium glutamicum ATCC13032 under both aerobic and anaerobic conditions. Under aerobic culture conditions, furfuryl alcohol and 2-furoic acid were produced as detoxification products of furfural. The ratio of the products varied depending on the initial furfural concentration. Neither furfuryl alcohol nor 2-furoic acid showed any toxic effect on cell growth, and both compounds were determined to be the end products of furfural degradation. Interestingly, unlike under aerobic conditions, most of the furfural was converted to furfuryl alcohol under anaerobic conditions, without affecting the glucose consumption rate. Both the NADH/NAD⁺ and NADPH/NADP⁺ ratio decreased in the accordance with furfural concentration under both aerobic and anaerobic conditions. These results indicate the presence of a single or multiple endogenous enzymes with broad and high affinity for furfural and co-factors in C. glutamicum ATCC13032.     

Screening microorganisms for utilization of furfural and possible intermediates in its degradative pathway

Summary A variety of microorganisms were screened for their ability to utilize furfural and possible intermediates in its degradative pathway. Compounds tested included furfural, furfuryl alcohol, 2-furoic acid, tetrahydrofurfuryl alcohol, di- and tetra-hydrofurans, 1,5-pentanediol and 1,4-butanediol. The objective of the research was to determine whether microbial strains might be found that degraded furfuryl via diols. If so, then it might be possible to block the metabolic pathway at the appropriate point allowing accumulation of diol(s). A promising bacterial strain was identified that could utilize furfural, some of its derivatives and diols, which is a candidate for further studies.     

糠醛和5-羟甲基糠醛对大肠杆菌产丁二酸的影响

利用可再生生物质特别是木质纤维素水解液来生产平台化合物丁二酸,是目前研究的热点。虽然许多研究者相继报道了木质纤维素水解液对菌株生长和丁二酸生产存在一定抑制作用,但并没有水解液中各种抑制物对菌株影响的相关动力学研究及机理研究。我们选择了两种代表性木质纤维素水解液抑制物,即糠醛和5-羟甲基糠醛,系统研究了它们对大肠杆菌的生长和丁二酸生产的影响。结果表明：糠醛和5-羟甲基糠醛的初始抑制浓度均为0.8 g/L。当糠醛浓度大于6.4 g/L,5-羟甲基糠醛浓度大于12.8 g/L时,菌株生长完全受到抑制。在最高耐受浓度下,糠醛的存在使菌株生物量比对照菌株下降77.8%,丁二酸产量下降36.1%。5-羟甲基糠醛的存在使菌株生物量比对照菌株降低13.6%,丁二酸产量降低18.3%。糠醛和5-羟甲基糠醛具有明显的协同作用。体外酶活测定表明丁二酸生产途径中关键酶磷酸烯醇式丙酮酸羧化酶、苹果酸脱氢酶、富马酸还原酶均受糠醛和5-羟甲基糠醛抑制。研究结果对丁二酸生产用纤维素水解液的预处理和脱毒工艺开发具有指导作用,有利于实现丁二酸发酵生产的工业化。