Role of reserve carbohydrates in the growth dynamics of

Abstract

The purpose of this study was to explore the role of glycogen and trehalose in the ability of Saccharomyces cerevisiae to respond to a sudden rise of the carbon flux. To this end, aerobic glucose-limited continuous cultures were challenged with a sudden increase of the dilution rate from 0.05 to 0.15 h(-1). Under this condition, a rapid mobilization of glycogen and trehalose was observed which coincided with a transient burst of budding and a decrease of cell biomass. Experiments carried out with mutants defective in storage carbohydrates indicated a predominant role of glycogen in the adaptation to this perturbation. However, the real importance of trehalose in this response was veiled by the unexpected phenotypes harboured by the tps1 mutant, chosen for its inability to synthesize trehalose. First, the biomass yield of this mutant was 25% lower than that of the isogenic wild-type strain at dilution rate of 0.05 h(-1), and this difference was annulled when cultures were run at a higher dilution rate of 0.15 h(-1). Second, the tps1 mutant was more effective to sustain the dilution rate shift-up, apparently because it had a faster glycolytic rate and an apparent higher capacity to consume glucose with oxidative phosphorylation than the wild type. Consequently, a tps1gsy1gsy2 mutant was able to adapt to the dilution rate shift-up after a long delay, likely because the detrimental effects from the absence of glycogen was compensated for by the tps1 mutation. Third, a glg1Deltaglg2Delta strain, defective in glycogen synthesis because of the lack of the glycogen initiation protein, recovered glycogen accumulation upon further deletion of TPS1. This recovery, however, required glycogen synthase. Finally, we demonstrated that the rapid breakdown of reserve carbohydrates triggered by the shift-up is merely due to changes in the concentrations of hexose-6-phosphate and UDPglucose, which are the main metabolic effectors of the rate-limiting enzymes of glycogen and trehalose pathways.

Short-Term Metabolome Dynamics and Carbon, Electron, and ATP Balances in Chemostat-Grown Saccharomyces cerevisiae CEN.PK 113-7D following a Glucose Pulse

“…The available intra-and extracellular metabolite measurements were combined with the in vivo q O 2 and q CO 2 values to construct the cumulative carbon, electron, and ATP balances. The measured glycogen concentrations in the insoluble residues and the cell extracts were ϳ3.1 mCmol Cmol x Ϫ1 and ϳ0.5 mCmol Cmol x Ϫ1 , respectively, which is much lower than the glycogen content of 102 mCmol Cmol x Ϫ1 reported for S. cerevisiae grown at 0.05 h Ϫ1 (13). The alkaline extraction seemed to be incomplete, presumably due to the use of insoluble residue obtained after boiling ethanol treatment rather than making the extraction directly from yeast cells, as previously described (27).…”

“…The carbon, electron, and ATP balances suggest that these as yet unmeasured carbon sinks have an average degree of reduction of 4.17 per Cmol and do not involve intensively energy-consuming pathways. One such carbon sink could be glycogen (degree of reduction per Cmol ϭ (13), complete conversion of the remaining unquantified carbon sinks to glycogen would increase the cellular glycogen content only 7%, which would require a highly accurate method of glycogen quantification for correct assessment.…”

“…Above this limit, the metabolic network would change due to the induction of gluconeogenic enzymes (9,44). For the Saccharomyces strain used in this study, the PP split ratio was estimated to be 0.44 and 0.24 in two 13 C-labeling studies (3,48), for ethanol fractions of 0 and 0.28 Cmol ethanol Cmol Ϫ1 , respectively, at a growth rate of 0.1 h Ϫ1 . For the feed used in this study (0.06 Cmol ethanol Cmol Ϫ1 ), a PP split ratio of 0.31 was interpolated and used to estimate the intracellular fluxes.…”

Mechanism of high trehalose accumulation in a spore clone isolated from Shirakami kodama yeast

“…It is known that tps1 mutants not only lack the ability to synthesize trehalose but also exhibit several pleiotropic defects including the inability to grow on glucose (Hohmann et al, 1992;Blázquez and Gancedo, 1995). These mutants have a sporulation deficiency (De and Cannon, 2001), while glycogen synthesis (Cannon et al, 1994;Torija et al, 2005) and respiration (Guillou et al, 2004) are also affected. Because Tps1 plays a key regulatory role in the control of yeast physiology, we questioned whether the function or expression of TPS1 in IB1304 cells could have been altered.…”

“…Trehalose levels in yeast cells result from the reciprocal activities of both trehalose synthase and trehalase (Trevisol et al, 2011) and it is known that ethanol stress induces transcription not only of TPS1 (Guillou et al, 2004;Fig. 2) but also of the neutral trehalase gene NTH1 (Alexandre et al, 2001).…”