Metabolic flux analysis of RQ‐controlled microaerobic ethanol production by <i>Saccharomyces cerevisiae</i>

Franzén, Carl Johan

doi:10.1002/yea.956

Cited by 50 publications

(55 citation statements)

References 67 publications

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“…The data here showed that reducing the glycerol yield by 50% by glucose feeding monitoring led to a 20% decrease in the ethanol yield to the benefit of biomass (30%), acetate, and succinate compared to the reference fermentation (Table 1). When the formation of glycerol was reduced in a microaerobic ethanolic fermentation in continuous culture by a carefully controlled oxygenation, a decrease in the ethanol yield was also observed (8). RQ-controlled fermentation led to a lower maximum specific ethanol production rate and average ethanol productivity; however, it was possible to reach high ethanol production (85 g · liter Ϫ1 in 30 h).…”

Section: Discussionmentioning

confidence: 99%

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Minimization of Glycerol Production during the High-Performance Fed-Batch Ethanolic Fermentation Process in Saccharomyces cerevisiae , Using a Metabolic Model as a Prediction Tool

Bideaux

Alfenore

Cameleyre

et al. 2006

Appl Environ Microbiol

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On the basis of knowledge of the biological role of glycerol in the redox balance of Saccharomyces cerevisiae, a fermentation strategy was defined to reduce the surplus formation of NADH, responsible for glycerol synthesis. A metabolic model was used to predict the operating conditions that would reduce glycerol production during ethanol fermentation. Experimental validation of the simulation results was done by monitoring the inlet substrate feeding during fed-batch S. cerevisiae cultivation in order to maintain the respiratory quotient (RQ) (defined as the CO 2 production to O 2 consumption ratio) value between 4 and 5. Compared to previous fermentations without glucose monitoring, the final glycerol concentration was successfully decreased. Although RQ-controlled fermentation led to a lower maximum specific ethanol production rate, it was possible to reach a high level of ethanol production: 85 g · liter ؊1 with 1.7 g · liter ؊1 glycerol in 30 h. We showed here that by using a metabolic model as a tool in prediction, it was possible to reduce glycerol production in a very high-performance ethanolic fermentation process.It is well-known that glycerol is a major by-product during alcoholic fermentation in the yeast Saccharomyces cerevisiae. The role of glycerol in the cellular redox balance (5) and in osmoregulation (4, 16) have been reported in the literature. Participating in the cell redox balance, glycerol is produced by Saccharomyces cerevisiae to reoxidize surplus NADH, formed in the synthesis of biomass and secondary fermentation products, to NAD ϩ (5). Two different strategies for modulating the production of glycerol have been reported in the literature. One strategy is to change the operating conditions of the fermentation process (i.e., aeration levels, stress conditions [salts, acids, osmotic stress, heat shock . . .]) (3,4,8,11,12,19,31,40,42); another is to use genetically modified strains. Engineered strains were constructed by overexpressing and repressing components of the glycerol synthesis pathway (14,18,19,21,25).Complementing biochemical and metabolic engineering experimental approaches, mathematical models may also be useful for interpretation and prediction of biochemical processes. Process models consist in coupling mass balance equations at the reactor scale and at the cellular scale (29). Cells can be modeled at different levels: unstructured models on the population level (15, 27) or structured models on the cellular level. The latter can be a compartmental model (41) or a metabolic regulator model (28). Constraints on carbon, energy, and redox potential linked to the metabolic network can be taken into account by a metabolic model that contains a complete set of metabolic pathways involved in biomass synthesis, energy production, substrate degradation, and cometabolite production (30,35).Metabolic flux analysis is generally used to quantify intracellular fluxes in the central metabolism of microorganisms (7,9,11,22,24,43), but it has had a limited impact due to the lack of regulatory...

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Section: Discussionmentioning

confidence: 99%

“….]) (3,4,8,11,12,19,31,40,42); another is to use genetically modified strains. Engineered strains were constructed by overexpressing and repressing components of the glycerol synthesis pathway (14,18,19,21,25).…”

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confidence: 99%

Minimization of Glycerol Production during the High-Performance Fed-Batch Ethanolic Fermentation Process in Saccharomyces cerevisiae , Using a Metabolic Model as a Prediction Tool

Bideaux

Alfenore

Cameleyre

et al. 2006

Appl Environ Microbiol

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“…The condition number of the stoichiometric matrix was 89, indicating a numerically well-conditioned system. The anaerobic model is presented and discussed in detail elsewhere (14). However, some important points are also mentioned here.…”

Section: Methodsmentioning

confidence: 99%

“…The cellular protein and RNA contents were measured as described above. The biomass was assumed to contain 5% lipids under aerobic conditions and 2% lipids under anaerobic conditions (average lipid compositions) (14,31). Under anaerobic conditions, unsaturated fatty acids, ergosterol, and inositol were assumed to be taken up from the medium, while under aerobic conditions only inositol was provided in the medium.…”

Section: Methodsmentioning

confidence: 99%

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Effects of Furfural on the Respiratory Metabolism of Saccharomyces cerevisiae in Glucose-Limited Chemostats

Horváth

Franzén

Taherzadeh

et al. 2003

Appl Environ Microbiol

148

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Effects of furfural on the aerobic metabolism of the yeast Saccharomyces cerevisiae were studied by performing chemostat experiments, and the kinetics of furfural conversion was analyzed by performing dynamic experiments. Furfural, an important inhibitor present in lignocellulosic hydrolysates, was shown to have an inhibitory effect on yeast cells growing respiratively which was much greater than the inhibitory effect previously observed for anaerobically growing yeast cells. The residual furfural concentration in the bioreactor was close to zero at all steady states obtained, and it was found that furfural was exclusively converted to furoic acid during respiratory growth. A metabolic flux analysis showed that furfural affected fluxes involved in energy metabolism. There was a 50% increase in the specific respiratory activity at the highest steady-state furfural conversion rate. Higher furfural conversion rates, obtained during pulse additions of furfural, resulted in respirofermentative metabolism, a decrease in the biomass yield, and formation of furfuryl alcohol in addition to furoic acid. Under anaerobic conditions, reduction of furfural partially replaced glycerol formation as a way to regenerate NAD ؉ . At concentrations above the inlet concentration of furfural, which resulted in complete replacement of glycerol formation by furfuryl alcohol production, washout occurred. Similarly, when the maximum rate of oxidative conversion of furfural to furoic acid was exceeded aerobically, washout occurred. Thus, during both aerobic growth and anaerobic growth, the ability to tolerate furfural appears to be directly coupled to the ability to convert furfural to less inhibitory compounds.An important problem in fermentative conversion of lignocellulose to ethanol is the severe inhibitory effects often exerted by lignocellulosic hydrolysates (17,21). Furfural is a characteristic compound present in dilute acid hydrolysates, particularly in hydrolysates from deciduous woods, in which the furfural concentration can be about 2 to 3 g/liter (37). Furfural has been found to severely inhibit metabolism in the yeast Saccharomyces cerevisiae under anaerobic conditions both during batch cultivation (5,7,27) and in glucose-limited chemostats (9,12,35). Furfural has been reported to have inhibitory effects on the specific growth rate, as well as on the fermentation rate of yeasts (4, 28). However, only few studies have described the effects of furfural under aerobic conditions. These effects are important, since inhibition caused by furfural during respiratory growth has a great impact on yeast propagation in an ethanol production plant based on a lignocellulosic feedstock. Taherzadeh et al. (39) compared the levels of conversion of furfural in anaerobic and aerobic batch cultures of S. cerevisiae growing on glucose. It was found that furfural was mainly converted to furfuryl alcohol by exponentially growing cells under both conditions and that the specific conversion rate was 0.6 g/g ⅐ h. Almost the same value for the maximum...

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Identification of flux regulation coefficients from elementary flux modes: A systems biology tool for analysis of metabolic networks

Nookaew

Meechai

Thammarongtham

et al. 2007

Biotech & Bioengineering

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Within a metabolic network, the elementary flux modes enables a unique description of different operations of the network. Thus, the metabolic fluxes can be specified as convex combinations of the elementary flux modes. Here, we describe an approach to identify the set of elementary flux modes that operates in a given metabolic network through the use of measurements of macroscopic fluxes, that is, fluxes in and out of the cell. Besides enabling estimation of the metabolic fluxes, the parameters of the linear combinations of the elementary flux modes provide valuable physiological information; we call these parameters flux regulation coefficients (FRCs). These coefficients indicate which enzyme subsets are important at different growth conditions. We demonstrate how FRCs can be used to map the operation of the metabolic network of the yeast Saccharomyces sp. under different growth conditions.

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

Cited by 50 publications

References 67 publications

Minimization of Glycerol Production during the High-Performance Fed-Batch Ethanolic Fermentation Process in Saccharomyces cerevisiae , Using a Metabolic Model as a Prediction Tool

Minimization of Glycerol Production during the High-Performance Fed-Batch Ethanolic Fermentation Process in Saccharomyces cerevisiae , Using a Metabolic Model as a Prediction Tool

Effects of Furfural on the Respiratory Metabolism of Saccharomyces cerevisiae in Glucose-Limited Chemostats

Identification of flux regulation coefficients from elementary flux modes: A systems biology tool for analysis of metabolic networks

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