Co-fermentation of grape must by Issatchenkia orientalis and Saccharomyces cerevisiae reduces the malic acid content in wine

Grape must was fermented by a mixed culture of Saccharomyces cerevisiae W-3 (a wine yeast) and Issatchenkia orientalis KMBL 5774 (a malic acid-degrading yeast). Co-fermentation with 1:1 (v/v) inoculum ratio of W-3 and KMBL 5774 decreased malic acid to 0.33 mg/ml from 1.1 mg ml with W-3 alone. Ethanol production was the same in both cases (7.8%, v/v). Acetaldehyde, 1-propanol, 2-butanol and isoamyl alcohol all decreased, with an increase in methanol, in the co-fermented wine. Sensory evaluation showed a higher score in the wine fermented with 1:1 (v/v) inoculum ratio than those obtained by 4:1 (v/v) inoculum ratio or W-3 alone.     

The metabolism of sugar and malic acid by Leuconostoc oenos: effect of malic acid, pH and aeration conditions

The co-metabolism of sugars by Leuconostoc oenos was studied under different environmental conditions. Under aerobic conditions, growth and sugar metabolism were poorer than under CO₂ or N₂ atmosphere and acetic acid accumulated to a larger extent. Glycerol was found in the aerobic cultures while erythritol was detected under N₂ or CO₂. When medium conditions make growth difficult (low pH, aerobic conditions, low nutrients), sugars were only slightly metabolized and growth was very slow while malic acid was rapidly and completely degraded, leading to an increase in the y _ATP. Aeration effects on the malic acid degradation rate depended on the nutrients and carbon source in the medium. Malic acid clearly stimulated bacterial growth, allowing an increase in the molar growth yields and ATP production. The results suggest that under adverse conditions cells are not able to grow and malic degradation supplies additional energy production.     

酿酒酵母产苹果酸的还原TCA路径构建及发酵调控

苹果酸广泛应用于食品、化工行业。文中通过在酿酒酵母内敲除丙酮酸脱羧酶PDC1,并通过构建胞质内还原TCA的路径,即超表达丙酮酸羧化酶和苹果酸脱氢酶,成功地实现了苹果酸的生产。在野生型菌株中基本检测不到苹果酸的生成,而在工程菌株,苹果酸发酵浓度达到了45 mmol /L,同时副产物乙醇的产量也降低了18%。进一步通过发酵调控提高第二信使Ca2+的浓度使苹果酸的产量提高了7 %,在此基础上提高丙酮酸羧化酶的辅酶生物素浓度,使苹果酸的产量达到52.5 mmol /L,较原始菌株提高了16%。     

Influence of pH on the rate of ribosomal ribonucleic acid synthesis during sporulation in Saccharomyces cerevisiae.

The rate of synthesis of ribosomal RNA (rRNA) is much slower during sporulation than during vegetative growth of yeast. If sporulating cells are transferred from normal incubation conditions at pH 8.8 to the same medium adjusted to pH 7.0, the rate of rRNA synthesis increased to approach that observed in vegetative cells. The response to the pH change is quite rapid, occurring within 10 min. THE PH-dependent, rate-limiting step appears to be in the processing of 35S ribosomal precursor RNA to the final 26S and 18S RNA species. A similar pH effect also was found for the rate of protein synthesis. However, no change in respiration was observed when the pH was lowered. These results indicate that the observed differences in rate of rRNA synthesis in vegetative and sporulating cells are a consequence of pH and are not intrinsic to sporulation. The results also support the correlation between rRNA processing and protein synthesis.     

Regulation of dipeptide transport in Saccharomyces cerevisiae by micromolar amino acid concentrations.

Prototrophic Saccharomyces cerevisiae X2180, when grown on unsupplemented minimal medium, displayed little sensitivity to ethionine- and m-fluorophenylalanine-containing toxic dipeptides. We examined the influence of the 20 naturally occurring amino acids on sensitivity to toxic dipeptides. A number of these amino acids, at concentrations as low as 1 microM (leucine and tryptophan), produced large increases in sensitivity to leucyl-ethionine, alanyl-ethionine, and leucyl-m-fluorophenylalanine. Sensitivity to ethionine and m-fluorophenylalanine remained high under either set of conditions. The addition of 0.15 mM tryptophan to a growing culture resulted in the induction of dipeptide transport, as indicated by a 25-fold increase in the initial rate of L-leucyl-L-[3H]leucine accumulation. This increase, which was prevented by the addition of cycloheximide, began within 30 min and peaked approximately 240 min after a shift to medium containing tryptophan. Comparable increases in peptidase activity were not apparent in crude cell extracts from tryptophan-induced cultures. We concluded that S. cerevisiae possesses a specific mechanism for the induction of dipeptide transport that can respond to very low concentrations of amino acids.     

Malic acid production and consumption by selected of Saccharomyces cerevisiae under anaerobic and aerobic conditions

Summary Fermentation tests in clearly defined laboratory conditions were carried out with eight functionally selected strains of Saccharomyces cerevisiae. Analysis of the data showed that there were no significant differences in malic acid production between the strains when the acid was initially present. When it was initially absent, however, significant differences were observed two strains (Nos. 1141 and 1083) showing marked productive superiority. With malic acid as the sole C source, two strains (Nos. 1109 and 1141) showed less acid consumption.     

Effect of pH and lactic or acetic acid on ethanol productivity by Saccharomyces cerevisiae in corn mash

The effects of lactic and acetic acids on ethanol production by Saccharomyces cerevisiae in corn mash, as influenced by pH and dissolved solids concentration, were examined. The lactic and acetic acid concentrations utilized were 0, 0.5, 1.0, 2.0, 3.0 and 4.0% w/v, and 0, 0.1, 0.2, 0.4, 0.8 and 1.6% w/v, respectively. Corn mashes (20, 25 and 30% dry solids) were adjusted to the following pH levels after lactic or acetic acid addition: 4.0, 4.5, 5.0 or 5.5 prior to yeast inoculation. Lactic acid did not completely inhibit ethanol production by the yeast. However, lactic acid at 4% w/v decreased (P<0.05) final ethanol concentration in all mashes at all pH levels. In 30% solids mash set at pH ≤5, lactic acid at 3% w/v reduced (P<0.05) ethanol production. In contrast, inhibition by acetic acid increased as the concentration of solids in the mash increased and the pH of the medium declined. Ethanol production was completely inhibited in all mashes set at pH 4 in the presence of acetic acid at concentrations ≥0.8% w/v. In 30% solids mash set at pH 4, final ethanol levels decreased (P<0.01) with only 0.1% w/v acetic acid. These results suggest that the inhibitory effects of lactic acid and acetic acid on ethanol production in corn mash fermentation when set at a pH of 5.0–5.5 are not as great as that reported thus far using laboratory media.     

Degradation of polygalacturonic acid by Saccharomyces cerevisiae

Thirty-three strains of Saccharomyces cereuisiae were tested for the ability to degrade polygalacturonic acid. Nine strains degraded polygalacturonic acid during growth in liquid or on solid medium supplemented with glucose. This ability of certain strains of S. cereuisiae may be important in the fermentation plant products.     

Inactivation by glucose of phosphoenolpyruvate carboxykinase from Saccharomyces cerevisiae

Phosphoenolpyruvate carboxykinase showed high activity in Saccharomyces cerevisiae grown on gluconeogenic carbon sources. Addition of glucose to such cultures caused a rapid loss of the phosphoenolpyruvate carboxykinase activity. Fructose or mannose had the same effect as glucose, while 2-deoxyglucose or galactose were without effect. The inactivation was an irreversible process, since the regain of the activity was dependent of de novo protein synthesis. Cycloheximide did not prevent inactivation. All strains of the genus Saccharomyces tested showed inactivation of their phosphoenolpyruvate carboxykinase upon addition of glucose; this behaviour was not restricted to this genus.Non-Standard Abbreviations FbPase fructose bisphosphatase [EC 3.1.3.11 fructose-1,6-bisphosphate hydrolase] - PEPCK phosphoenolpyruvate carboxykinase [EC 4.1.49 ATP: oxalacetate carboxylase (transphosphorylating)] - YPE yeast-peptone-ethanol A preliminary account of these results was presented at the Fourth International Symposium on Yeasts, Vienna, Austria, July 1974     

Effect of benzoic acid on glycolytic metabolite levels and intracellular pH in Saccharomyces cerevisiae.

Low concentrations of benzoic acid stimulated fermentation rates in Saccharomyces cerevisiae. At concentrations near the maximum permitting growth, there was inhibition of fermentation, lowered ATP and intracellular pH, and relatively greater accumulation of benzoate. Changes in the levels of glycolytic intermediates suggested that fermentation was inhibited as a result of high ATP usage rather than of lowered intracellular pH. Specific inhibition of phosphofructokinase or of several other glycolytic enzymes was not observed.     

Effect of benzoic acid on glycolytic metabolite levels and intracellular pH in Saccharomyces cerevisiae.

Low concentrations of benzoic acid stimulated fermentation rates in Saccharomyces cerevisiae. At concentrations near the maximum permitting growth, there was inhibition of fermentation, lowered ATP and intracellular pH, and relatively greater accumulation of benzoate. Changes in the levels of glycolytic intermediates suggested that fermentation was inhibited as a result of high ATP usage rather than of lowered intracellular pH. Specific inhibition of phosphofructokinase or of several other glycolytic enzymes was not observed.     

Improvement of lactic acid production in Saccharomyces cerevisiae by cell sorting for high intracellular pH

Yeast strains expressing heterologous L-lactate dehydrogenases can produce lactic acid. Although these microorganisms are tolerant of acidic environments, it is known that at low pH, lactic acid exerts a high level of stress on the cells. In the present study we analyzed intracellular pH (pHi) and viability by staining with cSNARF-4F and ethidium bromide, respectively, of two lactic-acid-producing strains of Saccharomyces cerevisiae, CEN.PK m850 and CEN.PK RWB876. The results showed that the strain producing more lactic acid, CEN.PK m850, has a higher pHi. During batch culture, we observed in both strains a reduction of the mean pHi and the appearance of a subpopulation of cells with low pHi. Simultaneous analysis of pHi and viability proved that the cells with low pHi were dead. Based on the observation that the better lactic-acid-producing strain had a higher pHi and that the cells with low pHi were dead, we hypothesized that we might find better lactic acid producers by screening for cells within the highest pHi range. The screening was performed on UV-mutagenized populations through three consecutive rounds of cell sorting in which only the viable cells within the highest pHi range were selected. The results showed that lactic acid production was significantly improved in the majority of the mutants obtained compared to the parental strains. The best lactic-acid-producing strain was identified within the screening of CEN.PK m850 mutants.     

Influence of acetate on growth kinetics and production control of Saccharomyces cerevisiae on glucose and ethanol

Summary The production and assimilation of acetate during the growth of Saccharomyces cerevisiae on glucose and ethanol have been studied. Acetate inhibits growth and causes decreased yields on both substrates. The usual respiratory quotient based policy for fed batch control cannot be used for highly acetate producing yeast because of compensation between O₂ over-consumption (due to acetate) and CO₂ over-production (due to ethanol) in case of glucose over-feeding.     

Factors affecting the consumption of 2,3-butanedione by Saccharomyces cerevisiae

Production and degradation of diacetyl by a commercial Saccharomyces cerevisiae strain was studied. This yeast did not produce diacetyl but could consume it. Diacetyl degradation activity was biological and was present even when the yeast was grown in the absence of diacetyl. Maximum specific activity was obtained when the yeast was grown in 280 μmol of diacetyl, 1 vvm of aeration and 37°C.     

Biosynthesis of valerenic acid by engineered Saccharomyces cerevisiae

Biotechnology Letters - To produce valerenic acid (VA) in Saccharomyces cerevisiae by engineering a heterologous synthetic pathway. Valerena-4,7(11)-diene synthase (VDS) derived from Valeriana...     

Regulation of invertase synthesis by glucose in Saccharomyces cerevisiae.

Saccharomyces cerevisiae growing under repressible conditions (1% of glucose or more) produces a burst of external invertase when shifted to higher temperatures. The secretion of this invertase requires protein synthesis, but was found to be independent of RNA formation. The level of mRNA accumulated and translated was inversely proportional to the glucose present in the growth medium. These results are consistent with the hypothesis that invertase is continuously synthesized both in the presence and absence of glucose, but under repressible conditions is degraded before secretion takes place.