Showing papers on "Fermentation published in 1991"

Genetic improvement of Escherichia coli for ethanol production: chromosomal integration of Zymomonas mobilis genes encoding pyruvate decarboxylase and alcohol dehydrogenase II.

Abstract: Zymomonas mobilis genes for pyruvate decarboxylase (pdc) and alcohol dehydrogenase II (adhB) were integrated into the Escherichia coli chromosome within or near the pyruvate formate-lyase gene (pfl) Integration improved the stability of the Z mobilis genes in E coli, but further selection was required to increase expression Spontaneous mutants were selected for resistance to high level of chloramphenicol that also expressed high levels of the Z mobilis genes Analogous mutants were selected for increased expression of alcohol dehydrogenase on aldehyde indicator plates These mutants were functionally equivalent to the previous plasmid-based strains for the fermentation of xylose and glucose to ethanol Ethanol concentrations of 544 and 416 g/liter were obtained from 10% glucose and 8% xylose, respectively The efficiency of conversion exceeded theoretical limits (051 g of ethanol/g of sugar) on the basis of added sugars because of the additional production of ethanol from the catabolism of complex nutrients Further mutations were introduced to inactivate succinate production (frd) and to block homologous recombination (recA)

Parametric studies of ethanol production form xylose and other sugars by recombinant Escherichia coli.

Abstract: The conversion of xylose to ethanol by recombinant Escherichia coli has been investigated in pH-controlled batch fermentations. Chemical and environmental parameters were varied to determine tolerance and to define optimal conditions. Relatively high concentrations of ethanol (56 g/L) were produced from xylose with excellent efficiencies. Volumetric productivities of up to 1.4 g ethanol/L h were obtained. Productivities, yields, and final ethanol concentrations achieved from xylose with recombinant E. coli exceeded the reported values with other organisms. In addition to xylose, all other sugar constituents of biomass (glucose, mannose, arabinose, and galactose) were efficiently converted to ethanol by recombinant E. coli. Unusually low inocula equivalent to 0.033 mg of dry cell weight/L were adequate for batch fermentations. The addition of small amounts of calcium, magnesium, and ferrous ions stimulated fermentation. The inhibitory effects of toxic compounds (salts, furfural, and acetate) which are present in hemicellulose hydrolysates were also examined.

Citrate Fermentation by Lactococcus and Leuconostoc spp

Abstract: Citrate and lactose fermentation are subject to the same metabolic regulation. In both processes, pyruvate is the key intermediate. Lactococcus lactis subsp. lactis biovar diacetylactis homofermentatively converted pyruvate to lactate at high dilution (growth) rates, low pH, and high lactose concentrations. Mixed-acid fermentation with formate, ethanol, and acetate as products was observed under conditions of lactose limitation in continuous culture at pH values above 6.0. An acetoin/butanediol fermentation with α-acetolactate as an intermediate was found upon mild aeration in continuous culture and under conditions of excess pyruvate production from citrate. Leuconostoc spp. showed a limited metabolic flexibility. A typical heterofermentative conversion of lactose was observed under all conditions in both continuous and batch cultures. The pyruvate produced from either lactose or citrate was converted to d-lactate. Citrate utilization was pH dependent in both L. lactis and Leuconostoc spp., with maximum rates observed between pH 5.5 and 6.0. The maximum specific growth rate was slightly stimulated by citrate, in L. lactis and greatly stimulated by citrate in Leuconostoc spp., and the conversion of citrate resulted in increased growth yields on lactose for both L. lactis and Leuconostoc spp. This indicates that energy is conserved during the metabolism of citrate.

Production of Alkaline Protease by a New Aspergillus flavus Isolate under Solid-Substrate Fermentation Conditions for Use as a Depilation Agent.

Abstract: The production of alkaline protease by an Aspergillus flavus strain isolated in our laboratory by solid-substrate fermentation for use as a depilation agent and the influence of various factors on enzyme production are reported. The optimum conditions for maximum production were a growth temperature of 32°C, 63% substrate moisture, and a growth period of 48 h. Enrichment with corn steep liquor or Casitone increased productivity. Scaling-up experiments indicated that flask-scale results could be reproduced at 1 and 30 kg of substrate. The enzyme preparation exhibited maximum activity at both pH 7.5 and pH 9.5. The use of this enzyme as a depilation agent was confirmed by experiments in a tannery.

Dilute-Acid Pretreatment of Corn Residues and Short-Rotation Woody Crops

Abstract: As a prerequisite for the enzymatic saccharification or simultaneous saccharification and fermentation process for ethanol synthesis, a dilute-acid pretreatment of the biomass has been shown to be a very effective first step in the yeast-catalyzed bioprocess. Three hardwoods (silver maple, sycamore, and black locust) and two corn residues (cobs and stover) were chosen and subjected to prehydrolysis with dilute sulfuric acid at 140 and 160 °C for reaction times ranging from 5 to 60 min. Although the hemicelluloses from all five samples could be completely hydrolyzed at both 140 and 160 °C, hydrolysis at 160 °C for the woods and stover produced a superior substrate for the cellulase enzyme from Trichoderma reesei, in which > 90% of the cellulose was hydrolyzed by the enzyme. Corn cobs produced an excellent substrate after only 5 min at 140°C. Small amounts of lignin and glucan were also solubilized by the acid in all samples.

Metabolic engineering of Klebsiella oxytoca M5A1 for ethanol production from xylose and glucose.

Abstract: The efficient diversion of pyruvate from normal fermentative pathways to ethanol production in Klebsiella oxytoca M5A1 requires the expression of Zymomonas mobilis genes encoding both pyruvate decarboxylase and alcohol dehydrogenase. Final ethanol concentrations obtained with the best recombinant, strain M5A1 (pLOI555), were in excess of 40 g/liter with an efficiency of 0.48 g of ethanol (xylose) and 0.50 g of ethanol (glucose) per g of sugar, as compared with a theoretical maximum of 0.51 g of ethanol per g of sugar. The maximal volumetric productivity per hour for both sugars was 2.0 g/liter. This volumetric productivity with xylose is almost twice that previously obtained with ethanologenic Escherichia coli. Succinate was also produced as a minor product during fermentation.

Optimization of L-malic acid production by Aspergillus flavus in a stirred fermentor.

Abstract: Effects of various nutritional and environmental factors on the accumulation of organic acids (mainly L-malic acid) by the filamentous fungus Aspergillus flavus were studied in a 16-L stirred fermentor. Improvement of the molar yield (moles acid produced per moles glucose consumed) of L-malic acid was obtained mainly by increasing the agitation rate (to 350 rpm) and the Fe(z+) ion concentration (to 12 mg/L) and by lowering the nitrogen (to 271 mg/L) and phosphate concentrations (to 1.5 mM) in the medium. These changes resulted in molar yields for L-malic acid and total C(4) acids (L-malic, succinic, and fumaric acids) of 128 and 155%, respectively. The high molar yields obtained (above 100%) are additional evidence for the operation of part of the reductive branch of the tricarboxylic acid cycle in L-malic acid accumulation by A. flavus. The fermentation conditions developed using the above mentioned factors and 9% CaCO(3) in the medium resulted in a high concentration (113 g/L L-malic acid from 120 g/L glucose utilized) and a high overall productivity (0.59 g/L h) of L-malic acid. These changes in acid accumulation coincide with increases in the activities of NAD(+)-malate dehydrogenase, fumarase, and citrate synthase.

Extractive fermentation for lactic acid production

Abstract: Lactic acid extractive fermentation was demonstrated using Alamine 336 in oleyl alcohol at acidic pH. The use of an efficient extraction system was possible through employment of the cell immobilization procedure. Process modeling was performed to relate the various process parameters such as flow rate, concentration, and pH. In experiments with 15% Alamine 336/oleyl alcohol, the bioreactor operation resulted in a higher productivity (12 g/L gel h) compared to that of a control fermentation (7 g/L gel h). Strategies for optimizing the extractive fermentation process were proposed considering both productivity and product recovery.

Malolactic fermentation: electrogenic malate uptake and malate/lactate antiport generate metabolic energy.

Abstract: The mechanism of metabolic energy production by malolactic fermentation in Lactococcus lactis has been investigated. In the presence of L-malate, a proton motive force composed of a membrane potential and pH gradient is generated which has about the same magnitude as the proton motive force generated by the metabolism of a glycolytic substrate. Malolactic fermentation results in the synthesis of ATP which is inhibited by the ionophore nigericin and the F0F1-ATPase inhibitor N,N-dicyclohexylcarbodiimide. Since substrate-level phosphorylation does not occur during malolactic fermentation, the generation of metabolic energy must originate from the uptake of L-malate and/or excretion of L-lactate. The initiation of malolactic fermentation is stimulated by the presence of L-lactate intracellularly, suggesting that L-malate is exchanged for L-lactate. Direct evidence for heterologous L-malate/L-lactate (and homologous L-malate/L-malate) antiport has been obtained with membrane vesicles of an L. lactis mutant deficient in malolactic enzyme. In membrane vesicles fused with liposomes, L-malate efflux and L-malate/L-lactate antiport are stimulated by a membrane potential (inside negative), indicating that net negative charge is moved to the outside in the efflux and antiport reaction. In membrane vesicles fused with liposomes in which cytochrome c oxidase was incorporated as a proton motive force-generating mechanism, transport of L-malate can be driven by a pH gradient alone, i.e., in the absence of L-lactate as countersubstrate. A membrane potential (inside negative) inhibits uptake of L-malate, indicating that L-malate is transported an an electronegative monoanionic species (or dianionic species together with a proton). The experiments described suggest that the generation of metabolic energy during malolactic fermentation arises from electrogenic malate/lactate antiport and electrogenic malate uptake (in combination with outward diffusion of lactic acid), together with proton consumption as result of decarboxylation of L-malate. The net energy gain would be equivalent to one proton translocated form the inside to the outside per L-malate metabolized.

Measurement of starch fermentation in the human large intestine.

Abstract: Starch, not fibre, is probably the major substrate for fermentation in the human colon. However, quantitating the amount of starch that resists pancreatic amylase and thus escapes digestion in the ...

Aureobasidins, new antifungal antibiotics. Taxonomy, fermentation, isolation, and properties.

Abstract: Aureobasidins A to R were isolated from the fermentation broth of Aureobasidium pullulans R106. Aureobasidins are cyclic depsipeptide antibiotics with MW's ranging from 1.070 to 1,148. Aureobasidins showed high in vitro antifungal activity against Candida albicans.

Metabolism of position-labelled glucose in anoxic methanogenic paddy soil and lake sediment

Abstract: Turnover times of radioactive glucose were shorter in paddy soil (4–16 min) than in Lake Constance sediment (18–62 min). In the paddy soil, 65–75% of the radioactive glucose was converted to soluble metabolites. In the sediment, only about 25% of the radioactive glucose was converted to soluble metabolites, the rest to particulate material. In anoxic paddy soil, the degradation pattern of position-labelled glucose was largely consistent with glucose degradation via the Embden-Meyerhof-Parnas (EMP) pathway followed by methanogenic acetate cleavage: CO2 mainly originated from C-3,4, whereas CH4 mainly originated from C-1 and C-6 of glucose. Acetate-carbon originated from C-1, C-2 and C-6 rather than from C-3,4 of glucose. In both paddy soil and Lake Constance sediment acetate and CO2 were the most important early metabolites of radioactive glucose. Other early products included propionate, ethanol/butyrate, succinate, and lactate, but accounted each for less than 1–8% of the glucose utilized. The labelling of propionate by [3,4-14C]glucose suggests that it was mainly produced from glucose or lactate rather than from ethanol. Isopropanol and caproate were also detectable in paddy soil, but were not produced from radioactive glucose. Chloroform inhibited methanogenesis, inhibited the further degradation of radioactive acetate and resulted in the accumulation of H2, however, did not inhibit glucose degradation. Since acetate was the main soluble fermentation product of glucose and was produced at a relatively high molar acetate: CO2 ratio (2.5:1), homoacetogenesis appeared to be the most important glucose fermentation pathway.

Glycerol fermentation of 1,3-propanediol by Clostridium butyricum . Measurement of product inhibition by use of a pH-auxostat

Abstract: The fermentation of glycerol to 1,3-propanediol, acetate, and butyrate by Clostridium butyricum was studied with respect to growth inhibition by the accumulating products. The clostridia were grown in a pH-auxostat culture at low cell density and product concentration and near maximum growth rate. The products were then added individually to the medium in increasing concentrations and the resulting depression of growth rate was used as a quantitative estimate of product inhibition. Under these conditions growth was totally inhibited at concentrations of 60 g/l for 1,3-propanediol, 27 g/l for acetic acid and 19 g/l for butyric acid at pH 6.5. Appreciable inhibition by glycerol was found only above a concentration of 80 g/l. In a pH-auxostat without added products but with high cell density as well as in batch cultures the product proportions were different. The 1,3-propanediol concentration may approach the value of complete inhibition while the concentrations of acetic and butyric acids remained below these values by at least one order of magnitude. It was therefore concluded that 1,3-propanediol is the first range inhibitor in this fermentation.

Continuous acetone-butanol-ethanol (ABE) fermentation using immobilized cells of Clostridium acetobutylicum in a packed bed reactor and integration with product removal by pervaporation.

Abstract: An integrated solvent (ABE) fermentation and product removal process was investigated. A stable solvent productivity of 3.5 g/L h was achieved by using cells of Clostridium acetobutylicum immobilized onto a packed bed of bonechar, coupled with continuous product removal by pervaporation. Using a concentrated feed solution containing lactose at 130g/L, a lactose value of 97.9% was observed. The integrated fermentation and product removal system, with recycling of the treated fermentor effluent containing only low amount of solvents (/but lactose and acids), leads to only low acid losses. Therefore, most of the acids are converted to solvents, and this results in a high solvent yield of 0.39 g solvents/g lactose utilized. The pervaporation system provided a high product removal rate even at low solvent concentrations. A solvent membrane flux of 7.1 g/m(2) h with a selectivity of 5 was achieved during these investigations. The system proved to be very reliable.

Isolation and physiological study of an amylolytic strain of Lactobacillus plantarum

Abstract: An amylolytic lactic acid bacterium identified as Lactobacillus plantarum was isolated from cassava roots (Manihot esculenta var. Ngansa) during reting. The amylolytic enzyme synthesized was an extracellular α-amylase with an optimum pH of 5.0 and an optimum temperature of 55° C. Cultured on starch, the strain displayed a growth rate of 0.43 h−1, a biomass yield of 0.19 g·g−1 and a lactate yield of 0.81 g·g−1. The growth kinetics were similar on starch and glucose. Sufficient enzyme was synthesized and starch hydrolysis was not a limiting factor for growth. Biosynthesis of the enzyme was observed when the glucose concentration was less than 6.7 g·l−1 and reached up to 4 IU·ml−1 at the end of the fermentation.

Propionic acid fermentation of lactose by Propionibacterium acidipropionici: effects of pH.

Abstract: Batch propionic acid fermentation of lactose by Propionibacterium acidipropionici were studied at various pH values ranging from 4.5 to 7.12. The optimum pH range for cell growth was between 6.0 and 7.1, where the specific growth rate was approximately 0.23 h(-1). The specific growth rate decreased with the pH in the acids have been identified as the two major fermentation products from lactose. The production of propionic acid was both growth and nongrowth associated, while acetic acid formation was closely associated with cell growth. The propionic acid yield increased with decreasing pH; It changed from approximately 33% (w/w) at pH 6.1-7.1 to approximately 63% at pH 4.5-5.0. In contrast, the acetic acid yield was not significantly affected by the pH; it remained within the range of 9%-12% at all pH values. Significant amounts of succinic and pyruvic acids were also formed during propionic acid fermentation of lactose. However, pyruvic acid was reconsumed and disappeared toward the end of the fermentation. The succinic acid yield generally decreased with the pH, from a high value of 17% at pH 7.0 to a low 8% at pH 5.0 Effects of growth nutrients present in yeast ex-tract on the fermentation were also studied. In general, the same trend of pH effects was found for fermentations with media containing 5 to 10 g/L yeast extract. However, More growth nutrients would be required for fermentations to be carried out efficienytly at acidic pH levels.

Xylitol production from D-xylose byCandida guillermondii: Fermentation behaviour

Abstract: The ability ofCandida guillermondii to produce xylitol from xylose and to ferment individual non xylose hemicellulosic derived sugars was investigated in microaerobic conditions. Xylose was converted into xylitol with a yield of 0,63 g/g and ethanol was produced in negligible amounts. The strain did not convert glucose, mannose and galactose into their corresponding polyols but only into ethanol and cell mass. By contrast, fermentation of arabinose lead to the formation of arabitol. On D-xylose medium,Candida guillermondii exhibited high yield and rate of xylitol production when the initial sugar concentration exceeded 110 g/l. A final xylitol concentration of 221 g/l was obtained from 300 g/l D-xylose with a yield of 82,6% of theoretical and an average specific rate of 0,19 g/g.h.

In vivo activation by ethanol of plasma membrane ATPase of Saccharomyces cerevisiae.

Abstract: Ethanol, in concentrations that affect growth and fermentation rates (3 to 10% [vol/vol]), activated in vivo the plasma membrane ATPase of Saccharomyces cerevisiae. The maximal value for this activated enzyme in cells grown with 6 to 8% (vol/vol) ethanol was three times higher than the basal level (in cells grown in the absence of ethanol). The Km values for ATP, the pH profiles, and the sensitivities to orthovanadate of the activated and the basal plasma membrane ATPases were virtually identical. A near-equivalent activation was also observed when cells grown in the absence of ethanol were incubated for 15 min in the growth medium with ethanol. The activated state was preserved after the extraction from the cells of the membrane fraction, and cycloheximide appeared to prevent this in vivo activation. After ethanol removal, the rapid in vivo reversion of ATPase activation was observed. While inducing the in vivo activation of plasma membrane ATPase, concentrations of ethanol equal to and greater than 3% (vol/vol) also inhibited this enzyme in vitro. The possible role of the in vivo activation of the plasma membrane proton-pumping ATPase in the development of ethanol tolerance by this fermenting yeast was discussed.

Isolation and characterization of microorganisms associated with the traditional sorghum fermentation for production of sudanese kisra.

Abstract: Sorghum flour obtained from Sudan was mixed with water in a 1:2 (wt/vol) ratio and fermented at 30°C for 24 h The bacterial populations increased with fermentation time and reached a plateau at approximately 18 h At the end of 24 h, sorghum batter pH had dropped from 595 to 395 and the batter had a lactic acid content of 080% The microbial population during the 24 h of fermentation consisted of bacteria (Pediococcus pentosaceus, Lactobacillus confusus, Lactobacillus brevis, Lactobacillus sp, Erwinia ananas, Klebsiella pneumoniae, and Enterobacter cloacae), yeasts (Candida intermedia and Debaryomyces hansenii), and molds (Aspergillus sp, Penicillium sp, Fusarium sp, and Rhizopus sp) P pentosaceus was the dominant microorganism at the end of the 24-h fermentation When three consecutive fermentations using an inoculum from the previous fermentation were carried out, the bacterial population increase plateaued at 9 h The microbial populations in these fermentations were dominated by P pentosaceus