Dynamics of Glycolytic Regulation during Adaptation of Saccharomyces cerevisiae to Fermentative Metabolism

Abstract

The ability of baker's yeast (Saccharomyces cerevisiae) to rapidly increase its glycolytic flux upon a switch from respiratory to fermentative sugar metabolism is an important characteristic for many of its multiple industrial applications. An increased glycolytic flux can be achieved by an increase in the glycolytic enzyme capacities (V max ) and/or by changes in the concentrations of low-molecular-weight substrates, products, and effectors. The goal of the present study was to understand the time-dependent, multilevel regulation of glycolytic enzymes during a switch from fully respiratory conditions to fully fermentative conditions. The switch from glucose-limited aerobic chemostat growth to full anaerobiosis and glucose excess resulted in rapid acceleration of fermentative metabolism. Although the capacities (V max ) of the glycolytic enzymes did not change until 45 min after the switch, the intracellular levels of several substrates, products, and effectors involved in the regulation of glycolysis did change substantially during the initial 45 min (e.g., there was a buildup of the phosphofructokinase activator fructose-2,6-bisphosphate). This study revealed two distinct phases in the upregulation of glycolysis upon a switch to fermentative conditions: (i) an initial phase, in which regulation occurs completely through changes in metabolite levels; and (ii) a second phase, in which regulation is achieved through a combination of changes in V max and metabolite concentrations. This multilevel regulation study qualitatively explains the increase in flux through the glycolytic enzymes upon a switch of S. cerevisiae to fermentative conditions and provides a better understanding of the roles of different regulatory mechanisms that influence the dynamics of yeast glycolysis.Baker's yeast (Saccharomyces cerevisiae) can rapidly switch between respiratory and fermentative sugar metabolism in response to changes in the availability of oxygen and fermentable sugars. This metabolic flexibility is likely to have arisen during evolution in environments where there are strong temporal and/or spatial fluctuations in sugar and oxygen levels. Upon transfer from respiratory to fermentative conditions, S. cerevisiae can, within a short time, tremendously increase its catabolic rates and start accumulating ethanol, as well as smaller amounts of acetate, succinate, and glycerol (50). In the natural, evolutionary context, this may have helped this organism rapidly monopolize sugars and create a hostile environment for competing microorganisms. This metabolic flexibility of S. cerevisiae is also an important characteristic for its multiple industrial applications. For instance, yeast biomass starved for glucose during storage has to rapidly adapt to a very high sugar concentration when it is added to bread dough or wort. Ideally, S. cerevisiae cells should be able to increase their CO 2 and ethanol production rates within minutes following their introduction into a fresh production medium. Upon such a transfer, the pathways responsi...

Integrated multilaboratory systems biology reveals differences in protein metabolism between two reference yeast strains

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“…After thawing and washing, the samples were extracted in acidic phenol/chloroform 33 before distribution. Samples for enzyme activity assays were collected by overpressure, quenched on ice and washed in potassium buffer before freezing and distribution 23 . Detailed descriptions of all sample processing protocols are provided as Supplementary Methods.…”

A new model for the aerobic metabolism of yeast allows the detailed analysis of the metabolic regulation during glucose pulse

“…[11][12][13]. Additionally, a few detailed models of aerobic, glucoselimited glycolysis do exist [4,[14][15][16][17], three of them with a focus on short-term behavior [4,14,15]. The models reproduce the experimental data rather well.…”

“…Short-term aerobic fermentation (within a few minutes) is driven solely by metabolic regulation evidenced by data showing unchanged enzyme capacities during this time span. In contrast, long-term aerobic fermentation (N45 min) is considered to occur via regulation of the expression of glucose-sensitive genes [4].…”

Optimisation of Cell Bioenergetics in Food-Associated Microorganisms

“…As has been reported, the shift from respiratory to fermentative metabolism resulted in a rapidly increase of the yeast glycolytic flux in order to compensate the differences in the ATP yield of the two metabolisms. The dynamics of glycolytic regulation during the adaptation of S. cerevisiae to fermentative metabolism have been investigated with the aim of understanding the time-dependent, multilevel regulation of glycolytic enzymes during the metabolic switch just described (van de Brink et al, 2008). It was reported that within 45 min of the switch from respiratory to fermentative metabolism, the glycolytic flux increases eightfold without any changes in the glycolytic enzymes' capacities, thereby highlighting an increase of the enzymes activities via metabolic regulation (i.e.…”