Physiological effects of nitrogen starvation in an anaerobic batch culture of Saccharomyces cerevisiae

Schulze, Ulrik; Lidén, Gunnar; Nielsen, Jens

doi:10.1099/13500872-142-8-2299

Cited by 61 publications

(48 citation statements)

References 68 publications

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“…This will further decrease the NADH formed per unit biomass. However, because of an increased turnover of protein, and excretion of organic acids, this decrease may be smaller than expected (Schulze et al, 1996). The optimum RQ for ethanol production under anabolic limitation may therefore differ from the results presented here.…”

Section: Nadh and Nadph Turnovercontrasting

confidence: 55%

“…If the biomass yield is reduced in this way, the amount of excess NADH formed due to biomass will decrease. Additionally, nitrogen starvation has been shown to cause a decrease in the cellular protein content, balanced by an increase in carbohydrates (Lillie and Pringle, 1980;Schulze et al, 1996;Shkidchenko, 1984). This will further decrease the NADH formed per unit biomass.…”

Section: Nadh and Nadph Turnovermentioning

confidence: 99%

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Metabolic flux analysis of RQ‐controlled microaerobic ethanol production by Saccharomyces cerevisiae

Franzén

2002

Yeast

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Microaerobic ethanol production by Saccharomyces cerevisiae CBS 8066 was investigated at different growth rates in respiratory quotient (RQ)-controlled continuous culture. The RQ was controlled by changing the inlet gas composition by a feedback controller while keeping other parameters constant. The ethanol yield increased slightly from the anaerobic values with decreasing RQ, reaching a broad maximum at RQ 20 to 12. There was little or no glycerol production at RQ values below 17 over a wide range of dilution rates. Metabolic flux analysis revealed that a decrease in the ethanol yield at RQ 6 coincided with the cyclic, oxidative operation of the TCA cycle reactions. The model indicated that respiratory dissimilation of glucose only occurs when the oxygen uptake rate is high enough to completely substitute for glycerol formation. The cytosolic and the mitochondrial NADH balances were important for determining the flux distributions. The smallest deviations between estimated and measured product yields were obtained when the unknown co-factor requirements of a limited number of biosynthetic reactions were chosen so that the amount of excess NADH formed in biosynthesis was minimized. The biomass yield was positively correlated with the net amount of NADH reoxidized in respiration and glycerol formation, indicating that the turnover of excess NADH from biosynthesis is an important factor influencing the biomass yield under oxygen-limiting conditions.

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Section: Nadh and Nadph Turnovercontrasting

confidence: 55%

Section: Nadh and Nadph Turnovermentioning

confidence: 99%

Metabolic flux analysis of RQ‐controlled microaerobic ethanol production by Saccharomyces cerevisiae

Franzén

2002

Yeast

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“…This is probably the reason for the high RNA level observed by Thomas and Batt (31), since in their experiments, growth proceeded rapidly in a complex medium. Moreover, it has been previously observed for Saccharomyces cerevisiae (28) and Klebsiella aerogenes (16) that growth under nitrogen-limiting conditions, as would be the case in the media employed in this study, leads to a low RNA concentration.…”

Section: Resultsmentioning

confidence: 95%

The Metabolic Network of Lactococcus lactis : Distribution of ¹⁴ C-Labeled Substrates between Catabolic and Anabolic Pathways

Novák

Loubière

2000

J Bacteriol

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Lactococcus lactis NCDO 2118 was grown in a simple synthetic medium containing only six essential amino acids and glucose as carbon substrates to determine qualitatively and quantitatively the carbon fluxes into the metabolic network. The specific rates of substrate consumption, product formation, and biomass synthesis, calculated during the exponential growth phase, represented the carbon fluxes within the catabolic and anabolic pathways. The macromolecular composition of the biomass was measured to distribute the global anabolic flux into the specific anabolic pathways. Finally, the distribution of radiolabeled substrates, both into the excreted fermentation end products and into the different macromolecular fractions of biomass, was monitored. The classical end products of lactic acid metabolism (lactate, formate, and acetate) were labeled with glucose, which did not label other excreted products, and to a lesser extent with serine, which was deaminated to pyruvate and represented approximately 10% of the pyruvate flux. Other minor products, keto and hydroxy acids, were produced from glutamate and branched-chain amino acids via deamination and subsequent decarboxylation and/or reduction. Glucose labeled all biomass fractions and accounted for 66% of the cellular carbon, although this represented only 5% of the consumed glucose.Lactic acid bacteria (LAB) are of great importance in the food industry, mainly for lactic acid production from various substrates, but also for flavor compound or bacteriocin synthesis. The nutritional complexity of LAB is such that they are frequently cultivated in media containing complex nitrogen sources (MRS [9] or M17 [30]) or in natural media (milk or wine) for different applications. However, the complexity of these media is such that growth and metabolic behavior are difficult to characterize precisely. This is certainly the reason why it is generally considered that during LAB fermentation, sugar is only a catabolic substrate leading to metabolic end products and energy while biomass is formed from anabolic precursors, i.e., amino acids, nucleotides, etc., present in the culture broth. Whatever the medium used, more than 90% of the carbon in the sugar is normally converted into metabolic end products, generally, lactic acid. Moreover, the growth of LAB is characterized by poor growth yield, i.e., amount of biomass formed per amount sugar consumed, and hence, the quantity of the biomass formed is low compared to the quantity of lactic acid produced. However, this simplistic model is based on inaccurate carbon balances and is very controversial. A very small part of the sugar leading to anabolic reactions could represent a significant part of the biomass carbon, and this consideration has been totally neglected.The study of radiolabeled substrate distribution into end products or biomass has been used to estimate the part of sugar leading to biomass. Sivakanesan and Dawes (29) reported that 0.5% of the glucose used as the substrate labeled the biomass of Staphylococcus epidermi...

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“…The final concentration of glycerol, quantitatively the second most important product of wine fermentation, was 7.8 g liter Ϫ1 , and glycerol was produced mainly during the exponential growth phase, in response to an imbalance in reduction equivalents triggered by protein synthesis (35). Other significant compounds produced by the yeast were succinic and acetic acids, whose final concentrations were 1.8 and 1.0 g liter Ϫ1 , respectively.…”

Section: Resultsmentioning

confidence: 99%

Biomass Content Governs Fermentation Rate in Nitrogen-Deficient Wine Musts

Varela

Pizarro

Agosín

2004

Appl Environ Microbiol

196

179

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Problematic fermentations are common in the wine industry. Assimilable nitrogen deficiency is the most prevalent cause of sluggish fermentations and can reduce fermentation rates significantly. A lack of nitrogen diminishes a yeast's metabolic activity, as well as the biomass yield, although it has not been clear which of these two interdependent factors is more significant in sluggish fermentations. Under winemaking conditions with different initial nitrogen concentrations, metabolic flux analysis was used to isolate the effects. We quantified yeast physiology and identified key metabolic fluxes. We also performed cell concentration experiments to establish how biomass yield affects the fermentation rate. Intracellular analysis showed that trehalose accumulation, which is highly correlated with ethanol production, could be responsible for sustaining cell viability in nitrogen-poor musts independent of the initial assimilable nitrogen content. Other than the higher initial maintenance costs in sluggish fermentations, the main difference between normal and sluggish fermentations was that the metabolic flux distributions in nitrogen-deficient cultures revealed that the specific sugar uptake rate was substantially lower. The results of cell concentration experiments, however, showed that in spite of lower sugar uptake, adding biomass from sluggish cultures not only reduced the time to finish a problematic fermentation but also was less likely to affect the quality of the resulting wine as it did not alter the chemistry of the must.Sluggish and stuck fermentations are common in the wine industry. Factors that affect the yeast growth rate and that lead to problematic fermentations include limited nutrient contents, ethanol toxicity, fatty acid toxicity, temperature extremes (5), the ratio of nitrogen sources to carbon sources in the medium (21), and the initial quantity and quality of the amino acids (29). Sluggish cultures may prolong the process time from days to weeks. In stuck fermentations, high levels of residual sugar are left following the arrest of fermentation. Several difficulties occur at the cellular level; these include diminished sugar transport capacity, the inability of yeasts to produce compatible solutes in response to high osmolality (20,28), and cell membrane integrity issues in the presence of high concentrations of ethanol (8). As such mechanisms may act simultaneously in cells and to various extents, it is difficult to isolate and reproduce the mechanisms in stuck and sluggish fermentations.Quantitatively, nitrogen is the second most abundant nutrient in wine fermentations. It is essential for yeast metabolism and growth. Consequently, a lack of nitrogen triggers sluggish fermentations (1,8,13). In previous studies workers found differences in nitrogen-related curves (e.g., curves of biomass versus assimilable nitrogen) which indicated that the fermentation rate and biomass yield functions are distinct (9, 10; W. Agenbach, Proc. S. Afr. Soc. Enol. Vitic., p. 66-88, 1977). In other studies the ...

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Physiological effects of nitrogen starvation in an anaerobic batch culture of Saccharomyces cerevisiae

Cited by 61 publications

References 68 publications

Metabolic flux analysis of RQ‐controlled microaerobic ethanol production by Saccharomyces cerevisiae

Metabolic flux analysis of RQ‐controlled microaerobic ethanol production by Saccharomyces cerevisiae

The Metabolic Network of Lactococcus lactis : Distribution of ¹⁴ C-Labeled Substrates between Catabolic and Anabolic Pathways

Biomass Content Governs Fermentation Rate in Nitrogen-Deficient Wine Musts

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Physiological effects of nitrogen starvation in an anaerobic batch culture of Saccharomyces cerevisiae

Cited by 61 publications

References 68 publications

Metabolic flux analysis of RQ‐controlled microaerobic ethanol production by Saccharomyces cerevisiae

Metabolic flux analysis of RQ‐controlled microaerobic ethanol production by Saccharomyces cerevisiae

The Metabolic Network of Lactococcus lactis : Distribution of 14 C-Labeled Substrates between Catabolic and Anabolic Pathways

Biomass Content Governs Fermentation Rate in Nitrogen-Deficient Wine Musts

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The Metabolic Network of Lactococcus lactis : Distribution of ¹⁴ C-Labeled Substrates between Catabolic and Anabolic Pathways