Showing papers on "Fermentation published in 1997"
TL;DR: The interaction of ruminally fermented carbohydrate and physically effective fiber must be considered when diets for dairy cattle are evaluated and formulated and variation in ruminal pH should be minimized by feeding management.
796 citations
TL;DR: The bioconversion process of lignocellulosics to ethanol could be successfully developed and optimized by aggressively applying the related novel science and technologies to solve the known key problems of conversion process.
646 citations
TL;DR: The delta pH-mediated anion accumulation provides a mechanistic explanation for the effect of fermentation acids on microbial ecology and metabolism.
Abstract: Anaerobic habitats often have low pH and high concentrations of fermentation acids, and these conditions can inhibit the growth of many bacteria. The toxicity of fermentation acids at low pH was traditionally explained by an uncoupling mechanism. Undissociated fermentation acids can pass across the cell membrane and dissociate in the more alkaline interior, but there is little evidence that they can act in a cyclic manner to dissipate protonmotive force. Fermentation acid dissociation in the more alkaline interior causes an accumulation of the anionic species, and this accumulation is dependent on the pH gradient (delta pH) across the membrane. Fermentation acid-resistant bacteria have low delta pH and are able to generate ATP and grow with a low intracellular pH. Escherichia coli O157:H7 is able to decrease its intracellular pH to 6.1 before growth ceases, but this modest decrease in delta pH can only partially counteract the toxic effect of fermentation anion accumulation. Fermentation acid-resistant bacteria are in most cases Gram-positive bacteria with a high intracellular potassium concentration, and even acid-sensitive bacteria like E. coli K-12 have increased potassium levels when fermentation acids are present. Intracellular potassium provides a counteraction for fermentation acid anions, and allows bacteria to tolerate even greater amounts of fermentation anions. The delta pH-mediated anion accumulation provides a mechanistic explanation for the effect of fermentation acids on microbial ecology and metabolism.
450 citations
TL;DR: This paper showed that butyric and propionic acids resulted in less methanogenesis than did amendment with ethanol or lactic acid, which generated much higher levels of H2 levels.
Abstract: Previous studies indicated that dechlorinators can utilize H2 at lower concentrations than can methanogens. This suggests a strategy for selective enhancement of dechlorinationmanaging H2 delivery so as to impart a competitive advantage to dechlorinators. Four H2 donorsbutyric and propionic acids, which can only be fermented when the H2 partial pressure is lower than 10-3.5 or 10-4.4 atm, respectively, and ethanol and lactic acid, which are readily fermented at H2 partial pressures 2−3 orders of magnitude higherwere administered to anaerobic mixed cultures. Comparison of the resulting enrichment cultures during time-intensive, short-term tests showed significant differences in patterns of donor degradation, H2 production and use, and distribution of reduction equivalents between dechlorination and competing methanogenesis. Amendment with butyric and propionic acids resulted in less methanogenesis than did amendment with ethanol or lactic acid, which generated much higher H2 levels. Ethanol did not support...
385 citations
TL;DR: The maximal hydrogen production potential by anaerobic bacteria is 1.3 to 2.2 mol-H2/mol-glucose, which is less than 50% of theoretical, and the fatty acid production from the vacuum cultures exhibited approximately the same yield of fatty acids as those of the non-vacuum cultures.
378 citations
TL;DR: It has been shown that the production of propionic acid is not always related to high hydrogen partial pressure, and when the operating pH was increased to 5.5, the yield of Propionic acid became significant.
Abstract: It has been found, in this study, that a new ethanol-type fermentation can be obtained in a continuous flow, high-rate acidogenic reactor receiving molasses as the feed. The operating pH must be maintained at about 4.5 to avoid onset of propionic fermentation. The acidogenic reactor had a VSS level of 20 g/L and its organic loading was as high as 80 to 90 kg COD/m(3) d. The operating ORP was around -250 mV. The ethanol-type fermentation was characterized by a simultaneous production of acetic acid and ethanol, while the yield of propionic was minimal even at a high organic loading rate of 80 to 90 kg COD/m(3) d, and also, the hydrogen partial pressure was as high as 50 kPa. Thus, this study has shown that the production of propionic acid is not always related to high hydrogen partial pressure. When the operating pH was increased to 5.5, the yield of propionic acid became significant.
359 citations
TL;DR: Calculations show that the yield of ATP during fermentation, although it is low relative to aerobic respiration, exceeds the amount that is likely to be required for maintenance, which appears to be very low in these cyanobacteria.
Abstract: Although cyanobacteria are oxygenic phototrophic organisms, they often thrive in environments that become periodically anoxic. This is particularly the case in the dark when photosynthetic oxygen evolution does not take place. Whereas cyanobacteria generally utilize endogenous storage carbohydrate by aerobic respiration, they must use alternative ways for energy generation under dark anoxic conditions. This aspect of metabolism of cyanobacteria has received little attention but nevertheless in recent years a steadily increasing number of publications have reported the capacity of fermentation in cyanobacteria. This review summarizes these reports and gives a critical consideration of the energetics of dark fermentation in a number of species. There are a variety of different fermentation pathways in cyanobacteria. These include homo- and heterolactic acid fermentation, mixed acid fermentation and homoacetate fermentation. Products of fermentation include CO2, H2, formate, acetate, lactate and ethanol. In all species investigated, fermentation is constitutive. All enzymes of the fermentative pathways are present in photoautotrophically grown cells. Many cyanobacteria are also capable of using elemental sulfur as electron acceptor. In most cases it seems unlikely that sulfur respiration occurs. The main advantage of sulfur reduction seems to be the higher yield of ATP which can be achieved during fermentation. Besides oxygen and elemental sulfur no other electron acceptors for chemotrophic metabolism are known so far in cyanobacteria. Calculations show that the yield of ATP during fermentation, although it is low relative to aerobic respiration, exceeds the amount that is likely to be required for maintenance, which appears to be very low in these cyanobacteria. The possibility of a limited amount of biosynthesis during anaerobic dark metabolism is discussed.
357 citations
TL;DR: Key enzymes in end product formation in Actinobacillus sp.
Abstract: Actinobacillus sp. 130Z fermented glucose to the major products succinate, acetate, and formate. Ethanol was formed as a minor fermentation product. Under CO2-limiting conditions, less succinate and more ethanol were formed. The fermentation product ratio remained constant at pH values from 6.0 to 7.4. More succinate was produced when hydrogen was present in the gas phase. Actinobacillus sp. 130Z grew at the expense of fumarate and l-malate reduction, with hydrogen as an electron donor. Other substrates such as more-reduced carbohydrates (e.g., d-sorbitol) resulted in higher succinate and/or ethanol production. Actinobacillus sp. 130Z contained the key enzymes involved in the Embden-Meyerhof-Parnas and the pentose-phosphate pathways and contained high levels of phosphoenolpyruvate (PEP) carboxykinase, malate dehydrogenase, fumarase, fumarate reductase, pyruvate kinase, pyruvate formate-lyase, phosphotransacetylase, acetate kinase, malic enzyme, and oxaloacetate decarboxylase. The levels of PEP carboxykinase, malate dehydrogenase, and fumarase were significantly higher in Actinobacillus sp. 130Z than in Escherichia coli K-12 and accounted for the differences in succinate production. Key enzymes in end product formation in Actinobacillus sp. 130Z were regulated by the energy substrates.
326 citations
TL;DR: Owing to the anatomy and physiology of the colon, putrefactive processes become quantitatively more important in the distal bowel, where carbohydrate is more limiting.
Abstract: In both health and disease, the colonic microbiota plays an important role in several areas of human physiology. This complex assemblage of microorganisms endows great metabolic potential on the large intestine, primarily through its degradative abilities. Many hundreds of different types of bacteria, varying widely in physiology and biochemistry, exist in a multitude of different microhabitats in the lumen of the large gut, the mucin layer and on mucosal surfaces. Both microbiota and host obtain clear benefits from association. For example, growth substrates from diet and body tissues, together with a relatively stable environment for bacteria to proliferate are provided by the host, which in turn has evolved to use butyrate, a bacterial fermentation product, as its principal source of energy for epithelial cells in the distal bowel. The main sources of carbon and energy for intestinal bacteria are complex carbohydrates (starches, non-starch polysaccharides). Carbohydrate metabolism is of great importance in the large intestine, since generically, and in terms of absolute numbers, the vast majority of culturable microorganisms are saccharolytic. The amounts and types of fermentation products formed by colonic bacteria depend on the relative amounts of each substrate available, their chemical structures and compositions, as well as the fermentation strategies (biochemical characteristics and catabolite regulatory mechanisms) of bacteria participating in depolymerization and fermentation of the substrates. Protein breakdown and dissimilatory amino acid metabolism result in the formation of a number of putatively toxic metabolites, including phenols, indoles and amines. Production of these substances is inhibited or repressed in many intestinal microorganisms by a fermentable source of carbohydrate. Owing to the anatomy and physiology of the colon, putrefactive processes become quantitatively more important in the distal bowel, where carbohydrate is more limiting.
316 citations
TL;DR: The relationship between in vitro gas production, concomitant in vitro apparent and true DM degradability and the partitioning of truly-degraded substrate between gas volume and microbial biomass yield and 15N incorporation into cells was examined.
Abstract: The relationship between in vitro gas production, concomitant in vitro apparent and true DM degradability has been examined in forty-two roughages. The partitioning of truly-degraded substrate between gas volume and microbial biomass yield and 15N incorporation into cells was also investigated. The relevance of this partitioning for the regulation of DM intake (DMI) was examined for fifty-four roughages. The results can be summarized as follows. In vitro gas production and in vitro apparent and true degradability are highly correlated (P < 0.0001), r being 0.96 and 0.95 respectively. There is an inverse relationship between in vitro gas production and microbial biomass yield (r--0.67, (P < 0.0001) and also 15N enrichment (P < 0.001) when the variables were related to a given unit of substrate truly degraded. Selecting roughages by in vitro gas production may well be a selection against maximum microbial yield and a combination of in vitro gas volume measurements with a complementary determination of the substrate truly degraded is proposed, to calculate a partitioning factor (PF) reflecting the variation of short-chain fatty acid production per unit substrate degraded. PF is calculated as the ratio, substrate truly degraded: gas produced by it. PF was highly significant (P < 0.0001) in DMI prediction when included in stepwise multiple correlations together with in vitro gas volume variables reflecting the extent and rate of gas production; 11% of the variation in DMI was accounted for by the PF. The total model, including extent and rate of gas production and the PF, accounted for 84% of the variation in DMI. Roughages producing proportionally less gas per unit substrate truly degraded had higher feed intakes.
309 citations
TL;DR: Results suggest that yeast culture provides soluble growth factors (i.e., organic acids, B vitamins, and amino acids) that stimulate growth of ruminal bacteria that utilize lactate and digest cellulose.
01 Jan 1997
TL;DR: The rumen has been shown to provide an efficiency of protein nutrition that is not available to non-ruminant herbivores by coprophagy as discussed by the authors, which is the primary source of amino acids for ruminants.
Abstract: The way in which the rumen has evolved as their first digestive organ potentially affords ruminants an efficiency of protein nutrition that is not available to non-ruminant herbivores. Protein is synthesized in the gut in the form of rumen microorganisms. The necessary energy is derived from plant polysaccharides such as cellulose, and the nitrogen is derived from ammonia and amino acids in the rumen. The energy and nitrogen sources can therefore be substrates of little value to most non-ruminants. Even more important, however, is the direct availability of that microbial protein for digestion and absorption by the host animal. Herbivores which employ hind-gut fermentation can only achieve the same efficiency of microbial protein utilization by coprophagy. In contrast, microbial protein is generally the ruminant’s principal source of amino acids.
TL;DR: In a continuous fermentation of glycerol by Klebsiella pneumoniae, a final propanediol concentration of 35.2–48.5 g l−1 and a volumetric productivity of 4.9-fold higher can be obtained at dilution rates between 0.1 and 0.25 h−1, correspond to about 80–96% of the theoretical maxima under ideal conditions.
TL;DR: The constructed pathway represents an alternative metabolic route for the fermentative production of dicarboxylic acids from renewable feedstocks and was analyzed kinetically in the forward and reverse directions.
Abstract: NAD(+)-dependent malic enzyme was cloned from the Escherichia coli genome by PCR based on the published partial sequence of the gene. The enzyme was overexpressed and purified to near homogeneity in two chromatographic steps and was analyzed kinetically in the forward and reverse directions. The Km values determined in the presence of saturating cofactor and manganese ion were 0.26 mM for malate (physiological direction) and 16 mM for pyruvate (reverse direction). When malic enzyme was induced under appropriate culture conditions in a strain of E. coli that was unable to ferment glucose and accumulated pyruvate, fermentative metabolism of glucose was restored. Succinic acid was the major fermentation product formed. When this fermentation was performed in the presence of hydrogen, the yield of succinic acid increased. The constructed pathway represents an alternative metabolic route for the fermentative production of dicarboxylic acids from renewable feedstocks.
TL;DR: Results indicate that intracellular ethanol production is simpler and less energy intensive than the conventional ethanol-fermentation process.
TL;DR: Results show that nitrate respiration and fermentation of B. subtilis are governed by divergent regulatory pathways, and suggest that PDH is involved in most or all acetyl coenzyme A production in B.subilis.
Abstract: Bacillus subtilis can grow anaerobically by respiration with nitrate as a terminal electron acceptor. In the absence of external electron acceptors, it grows by fermentation. Identification of fermentation products by using in vivo nuclear magnetic resonance scans of whole cultures indicated that B. subtilis grows by mixed acid-butanediol fermentation but that no formate is produced. An ace mutant that lacks pyruvate dehydrogenase (PDH) activity was unable to grow anaerobically and produced hardly any fermentation product. These results suggest that PDH is involved in most or all acetyl coenzyme A production in B. subtilis under anaerobic conditions, unlike Escherichia coli, which uses pyruvate formate lyase. Nitrate respiration was previously shown to require the ResDE two-component signal transduction system and an anaerobic gene regulator, FNR. Also required are respiratory nitrate reductase, encoded by the narGHJI operon, and moaA, involved in biosynthesis of a molybdopterin cofactor of nitrate reductase. The resD and resDE mutations were shown to moderately affect fermentation, but nitrate reductase activity and fnr are dispensable for fermentative growth. A search for genes involved in fermentation indicated that ftsH is required, and is also needed to a lesser extent for nitrate respiration. These results show that nitrate respiration and fermentation of B. subtilis are governed by divergent regulatory pathways.
TL;DR: Overexpression of GPD1 on synthetic must resulted in a substantial increase in glycerol production (×4) at the expense of ethanol, and acetaldehyde accumulated through the competitive regeneration of NADH via GPDH.
Abstract: The possibility of the diversion of carbon flux from ethanol towards glycerol in Saccharomyces cerevisiae during alcoholic fermentation was investigated. Variations in the glycerol 3-phosphate dehydrogenase (GPDH) level and similar trends for alcohol dehydrogenase (ADH), pyruvate decarboxylase and glycerol-3-phosphatase were found when low and high glycerol-forming wine yeast strains were compared. GPDH is thus a limiting enzyme for glycerol production. Wine yeast strains with modulated GPD1 (encoding one of the two GPDH isoenzymes) expression were constructed and characterized during fermentation on glucose-rich medium. Engineered strains fermented glucose with a strongly modified [glycerol] : [ethanol] ratio. gpd1delta mutants exhibited a 50% decrease in glycerol production and increased ethanol yield. Overexpression of GPD1 on synthetic must (200 g/l glucose) resulted in a substantial increase in glycerol production ( x 4) at the expense of ethanol. Acetaldehyde accumulated through the competitive regeneration of NADH via GPDH. Accumulation of by-products such as pyruvate, acetate, acetoin, 2,3 butane-diol and succinate was observed, with a marked increase in acetoin production.
TL;DR: All consumers today have a considerable portion of their nutritional needs met through fermented foods and beverages and this is likely to expand in the twenty-first century when world population reaches 8–12 billion.
TL;DR: In this paper, the solubilization of covalently bound phenolic acids during the fermentation of wheat bran in a human model colon was examined, and Xylanase and ferulic acid esterase activities were shown to be present.
Abstract: The action of wheat bran as a potential colon anticarcinogen is related partly to its low fermentability in the large intestine. Phenolic acids are highly bioactive components and also limit degradability of wheat bran in ruminants. Therefore, the solubilization of covalently bound phenolic acids during the fermentation of wheat bran in a human model colon was examined. Phenolics were only partially and relatively slowly solubilized from wheat bran, but were rapidly and fully solubilized from sugarbeet fiber; the levels of free ferulic acid in fermentation liquors remained very low and did not reflect the amounts solubilized from fiber sources. Xylanase and ferulic acid esterase activities were shown to be present. The released ferulic acid did not appear to bind noncovalently to the residual wheat bran fiber. Thus, fermentation in the gut alters the partition of esterified phenolic acids from the insoluble residue and the soluble fraction, where microbial ferulic acid esterase(s) can potentially yield fr...
TL;DR: Carbon balance following fermentation by C. beijerinckii 8052 and BA101 indicates that sufficient carbon is available for the twofold increase in butanol concentration observed during BA101 fermentations.
Abstract: Dramatically elevated levels of butanol and acetone resulted in higher butanol and total solvent yields for hyperamylolytic Clostridium beijerinckii BA101 relative to the NCIMB 8052 parent strain grown in semidefined P2 medium containing either 6% glucose or STAR-DRI 5 maltodextrin. C. beijerinckii BA101 consistently produced on the order of 19 g of butanol per liter in 20-liter batch fermentations. This represents a greater than 100% increase in butanol concentration by the BA101 strain compared to the parent NCIMB 8052 strain. The kinetics of butanol production over time also indicate a more rapid rate of butanol production by BA101 in semidefined P2 medium containing glucose or maltodextrin. The lower levels of butyric and acetic acids produced over the course of the fermentation carried out by BA101 are consistent with an enhanced capacity for uptake and recycling of these acids. C. beijerinckii BA101 appears to more completely utilize carbohydrate compared to the 8052 strain. Carbon balance following fermentation by C. beijerinckii 8052 and BA101 indicates that sufficient carbon is available for the twofold increase in butanol concentration observed during BA101 fermentations. C. beijerinckii BA101 also has superior solvent production capacity during continuous culture fermentation in P2 medium containing 6% glucose. Volumetric solvent yields of 0.78 and 1.74 g/liter/h for BA101 and 0.34 and 1.17 g/liter/h for NCIMB 8052 were obtained at dilution rates of 0.05 and 0.20 h(sup-1), respectively. No drift towards acid synthesis (strain degeneration) was observed for up to 200 h (d = 0.05 h(sup-1)) and 100 h (d = 0.20 h(sup-1)).
TL;DR: The principal anti-microbial factor identified is the ability of all LAB to produce organic acids and decrease the pH of foods in which they grow.
TL;DR: Recent advances in the development of controlled gene expression systems, which allow the regulated overproduction of any desirable protein by lactic acid bacteria, are described.
TL;DR: Progressive change of pH from an initial value of 5.0 down to 4.3 has significantly improved the overall performance of the simultaneous saccharification and extractive fermentation over that of constant pH operation.
Abstract: Lactic acid production from cellulosic biomass by cellulase and Lactobacillus delbrueckii was studied in a fermenter-extractor employing a microporous hollow fiber membrane (MHF). This bioreactor system was operated under a fed-batch mode with continuous removal of lactic acid by an in situ extraction. A tertiary amine (Alamine 336) was used as an extractant for lactic acid. The extraction capacity of Alamine 336 is greatly enhanced by addition of alcohol. Long-chain alcohols serve well for this purpose since they are less toxic to micro-organism. Addition of kerosene, a diluent, was necessary to reduce the solvent viscosity. A solvent mixture of 20% Alamine 336, 40% oleyl alcohol, and 40% kerosene was found to be most effective in the extraction of lactic acid. Progressive change of pH from an initial value of 5.0 down to 4.3 has significantly improved the overall performance of the simultaneous saccharification and extractive fermentation over that of constant pH operation. The change of pH was applied to promote cell growth in the early phase, and extraction in the latter phase.
TL;DR: In this paper, a combination of germination and fermentation is a potential process for decreasing the antinutrient levels and enhancing digestibility of finger millet, which is a source of carbohydrate, protein and mineral that is comparable to other common cereal grains.
TL;DR: Production of lactic acid and a suspected competition with yeast cells for essential growth factors in the fermenting medium were the major reasons for reductions in yeast growth and final ethanol yield when lactic Acid bacteria were present.
Abstract: Normal-gravity (22 to 24 degrees Plato) wheat mashes were inoculated with five industrially important strains of lactobacilli at approximately 10(5), approximately 10(6), approximately 10(7), approximately 10(8), and approximately 10(9) CFU/ml in order to study the effects of the lactobacilli on yeast growth and ethanol productivity. Lactobacillus plantarum, Lactobacillus paracasei, Lactobacillus #3, Lactobacillus rhamnosus, and Lactobacillus fermentum were used. Controls with yeast cells but no bacterial inoculation and additional treatments with bacteria alone inoculated at approximately 10(7) CFU/ml of mash were included. Decreased ethanol yields were due to the diversion of carbohydrates for bacterial growth and the production of lactic acid. As higher numbers of the bacteria were produced (depending on the strain), 1 to 1.5% (wt/vol) lactic acid resulted in the case of homofermentative organisms. L. fermentum, a heterofermentative organism, produced only 0.5% (wt/vol) lactic acid. When L. plantarum, L. rhamnosus, and L. fermentum were inoculated at approximately 10(6) CFU/ml, an approximately 2% decrease in the final ethanol concentration was observed. Smaller initial numbers (only 10(5) CFU/ml) of L. paracasei or Lactobacillus #3 were sufficient to cause more than 2% decreases in the final ethanol concentrations measured compared to the control. Such effects after an inoculation of only 10(5) CFU/ml may have been due to the higher tolerance to ethanol of the latter two bacteria, to the more rapid adaptation (shorter lag phase) of these two industrial organisms to fermentation conditions, and/or to their more rapid growth and metabolism. When up to 10(9) CFU of bacteria/ml was present in mash, approximately 3.8 to 7.6% reductions in ethanol concentration occurred depending on the strain. Production of lactic acid and a suspected competition with yeast cells for essential growth factors in the fermenting medium were the major reasons for reductions in yeast growth and final ethanol yield when lactic acid bacteria were present.
TL;DR: High cell density fed-batch fermentation of Alcaligenes eutrophus was carried out for the production of poly(3-hydroxybutyrate) (PHB) in a 60-L fermentor and the effect of initial phosphate concentration on the PHB production when the initial volume was fixed was investigated.
Abstract: High cell density fed-batch fermentation of Alcaligenes eutrophus was carried out for the production of poly(3-hydroxybutyrate) (PHB) in a 60-L fermentor. During the fermentation, pH was controlled with NH(4)OH solution and PHB accumulation was induced by phosphate limitation instead of nitrogen limitation. The glucose feeding was controlled by monitoring dissolved oxygen (DO) concentration and glucose concentration in the culture broth. The glucose concentration fluctuated within the range of 0-20 g/L. We have investigated the effect of initial phosphate concentration on the PHB production when the initial volume was fixed. Using an initial phosphate concentration of 5.5 g/L, the fed-batch fermentation resulted in a final cell concentration of 281 g/L, a PHB concentration of 232 g/L, and a PHB productivity of 3.14 g/L . h, which are the highest values ever reported to date. In this case, PHB content, cell yield from glucose, and PHB yield from glucose were 80, 0.46, and 0.38% (w/w), respectively.
TL;DR: In this paper, a 2 4 full factorial central composite experimental design followed by multi-stage Monte-Carlo optimization was used in the design of experiments and in the analysis of results.
Abstract: Optimization of the fermentation media for maximization of surfactin production was carried out. The carbon source (glucose), the nitrogen source (ammonium nitrate) and the mineral salts ferrous and manganous sulphates were the critical components of the medium optimized. A 2 4 full factorial central composite experimental design followed by multi-stage Monte-Carlo optimization was used in the design of experiments and in the analysis of results. This procedure limited the number of actual experiments performed while allowing for possible interactions between the four components. The optimum values for the tested variables for the maximal production of surfactin were (in g dm -3 ): glucose = 36.5; NH 4 NO 3 = 4.5; FeSO 4 = 4 x 10 -3 and MnSO 4 = 27.5 x 10 -2 . Relative surfactant concentrations were expressed as the reciprocal of the critical micelle concentration (CMC -1 ) and the maximum predicted yield of surfactin in terms of CMC -1 was 45.5.
TL;DR: In this paper, a haploid wine strain of Saccharomyces cerevisia was grown on synthetic or natural winery musts and the expression profiles of nine genes, including members of the HSP family, were analyzed.
Abstract: Genetic engineering of wine yeast strains requires the identification of gene promoters specifically activated under wine processing conditions. In this study, transcriptional activation of specific genes was followed during the time course of wine fermentation by quantifying mRNA levels in a haploid wine strain ofSaccharomyces cerevisiaegrown on synthetic or natural winery musts. Northern analyses were performed using radioactive probes from 19 genes previously described as being expressed under laboratory growth conditions or on molasses in S. cerevisiae during the stationary phase and/or under nitrogen starvation. Nine genes, including members of the HSP family, showed a transition-phase induction profile. For three of them, mRNA transcripts could be detected until the end of the fermentation. Expression of one of these genes, HSP30, was further studied using a HSP30::lacZ fusion on both multicopy and monocopy expression vectors. The production of ‚-galactosidase by recombinant cells was measured during cell growth and fermentation on synthetic and natural winery musts. We showed that the HSP30 promoter can induce high gene expression during late stationary phase and remains active until the end of the wine fermentation process. Similar expression profiles were obtained onfive natural winery musts. ?1997 by John Wiley & Sons, Ltd.
TL;DR: The results support a model for cms-T-type male sterility in maize, in which degeneration of the tapetum is caused by the toxic effects of acetaldehyde on mitochondria weakened by the presence of the URF13 protein.
Abstract: In vegetative organs of plants, the metabolic switch from respiration to fermentation is dictated by oxygen availability The two genes dedicated to ethanolic fermentation, pyruvate decarboxylase and alcohol dehydrogenase, are induced by oxygen deprivation and the gene products are active under oxygen stress In pollen, these two genes are expressed in a stage-specific manner and transcripts accumulate to high levels, irrespective of oxygen availability We have examined the expression pattern of pyruvate decarboxylase and alcohol dehydrogenase at the protein level in developing pollen and show that the active proteins are localized to the gametophytic tissue and begin to accumulate at microspore mitosis A flux through the ethanolic fermentation pathway could already be detected very early in pollen development, occurring in all stages from premeiotic buds to mature pollen This flux was primarily controlled not by oxygen availability, but rather by sugar supply At a high rate of sugar metabolism, respiration and fermentation took place concurrently in developing and germinating pollen We propose that aerobic fermentation provides a shunt from pyruvate to acetyl-CoA to accommodate the increased demand for energy and biosynthetic intermediates during pollen development and germination A possible undesirable side-effect is the potential accumulation of toxic acetaldehyde Our results support a model for cms-T-type male sterility in maize, in which degeneration of the tapetum is caused by the toxic effects of acetaldehyde on mitochondria weakened by the presence of the URF13 protein