Impact du dioxyde de carbone sur la levure Saccharomyces cerevisiae : caractérisation du transfert liquide/gaz et implications sur les métabolismes énergétiques

The aim of this work was to evaluate the impact of carbon dioxide (CO2) on the physiology of the yeast Saccharomyces cerevisiae, more precisely on the oxidative metabolism and on the onset of alcoholic fermentation. CO2 is involved in the interactions between transfer phenomena and biological phenomena in fermenters. The knowledge of the dissolved CO2 concentration and then of the CO2 liquid / gas mass transfer phenomena is required to assess the impact of this compound on the yeast physiology.Investigation of CO2 liquid / gas in biological reactors has been carried out using simulations and experiments taking into consideration both biological and transfer phenomena. CO2 supersaturation was observed in an intensive fed-batch culture of S.cerevisiae and may be caused by an asymmetric bubble size distribution of the gas phase. We demonstrated that CO2 liquid / gas transfer cannot be described based on O2 gas / liquid transfer and that CO2 concentration must be estimated through direct measurement.The impact of CO2 on the oxidative metabolism of S.cerevisiae was investigated using chemostat cultures submitted to different step-increases of the dissolved CO2 concentrations with direct measurement of the dissolved CO2 concentration. The yeast culture showed a transient response with an increase of the specific respiration rates ranging from with a +24 to +37 % during + 2.96 mM and+5.29 mM dissolved CO2 step-increases. This transient response was followed by a long-term response characterized by a decrease of the YATP value with increasing dissolved CO2 concentrations (down to -18% when the CO2 concentration increased from 1.6 mM to 17 mM).The impact of CO2 on the onset of the Crabtree effect in S.cerevisiae was investigated using the accelerostat technique with and without CO2 enrichment. The onset of alcoholic fermentation occurred at a much lower specific growth rate (0.122 h-1) and specific oxygen consumption rate (5.2 mmoleO2.gX-1.h-1) in CO2 enriched conditions than without CO2 enrichment (0.256h-1 and 8.65 mmoleO2.gX-1.h-1 respectively). These modifications may be linked with a decreased cellular adaptability to changing environmentL’objectif de ce travail est l’étude de l’impact du dioxyde de carbone (CO2) sur la physiologie et le métabolisme de la levure Saccharomyces cerevisiae, en particulier son impact sur le catabolisme oxydatif du glucose et son rôle dans le déclenchement de la transition respiro-fermentaire. Le CO2 est au coeur des interactions entre phénomènes biologiques et phénomènes physiques de transfert existant au sein d’un réacteur biologique. La compréhension de son impact sur la physiologie de la levure nécessite la connaissance de sa concentration en phase liquide et donc la maitrise des phénomènes de transfert interphasiques.Le transfert liquide / gaz du CO2 en fermenteur a été étudié par une approche couplant modélisation et expérimentation avec un effort particulier sur l’analyse intégrée des phénomènes biologiques et de transfert. En comparaison avec les hypothèses de transfert généralement admises une sursaturation du moût en CO2 dissous dans le moût a été observée lors de cultures de S.cerevisiae et attribuée à l‘existence d’une distribution asymétrique de tailles de bulles de la phase dispersée. Il a été démontré que le transfert liquide / gaz du CO2 lors d’une culture microbienne intensive ne peut être décrit par analogie avec le transfert gaz / liquide de l’oxygène et que la connaissance de la concentration en CO2 dissous ne peut être réalisée que par sa mesure directe.L’impact du CO2 sur le métabolisme oxydatif de la levure a été investigué par le suivi de la réponse dynamique de la réponse à différents incréments mesurés de la concentration en CO2 dissous en culture continue. Cette réponse est constituée d’une réponse transitoire et intense et d’une réponse à long-terme plus modérée Elle se caractérise par l’impact du CO2 sur l’énergétique cellulaire en augmentant la génération et la dissipation d’énergie ce qui est traduit à court-terme par une augmentation transitoire de +24 à +37 % des vitesses spécifiques de respiration lors d’échelons de la concentration en CO2 dissous de +2.96 et +5.29 mM et à long-terme par une diminution de 18% YATP de % lorsque la concentration en CO2 dissous augmente de 1.6 mM à 17 mM. L’effet du CO2 sur la transition respiro-fermentaire a été étudié en culture de type accélérostat en présence d’une concentration élevée en CO2 dissous. Dans ces conditions, la bascule vers le métabolisme réductif est obtenue pour un taux de croissance (0.122 h-1) et des vitesses spécifiques de respiration (5.2 mmoleO2.gX-1.h-1) inférieurs aux valeurs obtenues avec un accélérostat sans apport exogène de CO2 (0.256h-1 et 8.65 mmoleO2.gX-1.h-1) respectivement. Cette modification du métabolisme n’a pu être corrélée directement à un déficit de potentiel énergétique oxydatif et semble probablement liée à une perte de flexibilité d’adaptation à la dynamique de variation de l’environnement

Thermal sensitivity of cell metabolism of different Antarctic fish species mirrors organism temperature tolerance

Despite cold adaptation, Antarctic fish show lower growth than expected from the van’t Hoff’s Q10 rule. Protein synthesis is one of the main energy-consuming processes, which is downregulated under energy deficiency. Considering the effect of temperature on growth performance, we tested if temperature-dependent cellular energy allocation to protein synthesis correlates with temperature-dependent whole-animal growth and thus thermal tolerance. Cell respiration and energy expenditure for protein synthesis were determined in hepatocytes of the circumpolar-distributed Antarctic eelpout Pachycara brachycephalum after warm acclimation (0 °C vs 5 °C) and, of two notothenioids the sub-Antarctic Lepidonotothen squamifrons and the high-Antarctic icefish Chionodraco hamatus. We used intermittent-flow respirometry to analyse cellular response to acute warming from 5 to 10 °C (P. brachycephalum) and from 1 to 5 °C (L. squamifrons, C. hamatus). Warming-induced rise in respiration was similar between 0- and 5 °C-acclimated P. brachycephalum and between L. squamifrons and C. hamatus. Irrespective of acclimation, warming decreased energy expenditure for protein synthesis in P. brachycephalum, which corresponds to reduced whole-animal growth at temperatures > 5 °C. Warming doubled energy expenditure for protein synthesis in L. squamifrons but had no effect on C. hamatus indicating that L. squamifrons might benefit from warmer waters. The species-specific temperature effect on energy expenditure for protein synthesis is discussed to mirror thermal sensitivity of whole-animal growth performance, thereby paralleling the degree of cold adaptation. Clearly more data are necessary including measurements at narrower temperature steps particularly for C. hamatus and an increased species’ number per ecotype to reinforce presented link between cellular and whole-animal thermal sensitivity

Temperature but not ocean acidification affects energy metabolism and enzyme activities in the blue mussel, Mytilus edulis

1. In mosaic marine habitats, such as intertidal zones, ocean acidification (OA) is exacerbated by high variability of pH, temperature, and biological CO2 production. The nonlinear interactions among these drivers can be context-specific and their effect on organisms in these habitats remains largely unknown, warranting further investigation. 2. We were particularly interested in Mytilus edulis (the blue mussel) from intertidal zones of the Gulf of Maine (GOM), USA, for this study. GOM is a hot spot of global climate change (average sea surface temperature (SST) increasing by \u3e0.2°C/year) with \u3e60% decline in mussel population over the past 40 years. 3. Here, we utilize bioenergetic underpinnings to identify limits of stress tolerance in M. edulis from GOM exposed to warming and OA. We have measured whole organism oxygen consumption rates and metabolic biomarkers in mussels exposed to control and elevated temperatures (10 vs. 15°C, respectively) and current and moderately elevated PCO2 levels (~400 vs. 800 µatm, respectively). 4. Our study demonstrates that adult M. edulis from GOM are metabolically resilient to the moderate OA scenario but responsive to warming as seen in changes in metabolic rate, energy reserves (total lipids), metabolite profiles (glucose and osmolyte dimethyl amine), and enzyme activities (carbonic anhydrase and calcium ATPase). 5. Our results are in agreement with recent literature that OA scenarios for the next 100–300 years do not affect this species, possibly as a consequence of maintaining its in vivo acid-base balance

1H-NMR-Based Metabolic Profiling in Muscle and Liver Tissue of Juvenile Turbot (Scophthalmus maximus) Fed with Plant and Animal Protein Sources

Circular economy driven feed ingredients and emerging protein sources, such as insects and microbial meals, has the potential to partially replace fishmeal in diets of high-trophic fish. Even though growth and feed performance are often unaffected at low inclusion levels, the metabolic effects are unknown. This study examined the metabolic response of juvenile turbot (Scophthalmus maximus) to diets with graded fishmeal replacement with plant, animal, and emerging protein sources (PLANT, PAP, and MIX) in comparison to a commercial-like diet (CTRL). A 1H-nuclear magnetic resonance (NMR) spectroscopy was used to assess the metabolic profiles of muscle and liver tissue after feeding the fish the experimental diets for 16 weeks. The comparative approach revealed a decrease in metabolites that are associated with energy deficiency in both tissues of fish fed with fishmeal-reduced diets compared to the commercial-like diet (CTRL). Since growth and feeding performance were unaffected, the observed metabolic response suggests that the balanced feed formulations, especially at lower fishmeal replacement levels, have the potential for industry application

Impact of Ocean Acidification on Energy Metabolism of Oyster, Crassostrea gigas—Changes in Metabolic Pathways and Thermal Response

Climate change with increasing temperature and ocean acidification (OA) poses risks for marine ecosystems. According to Pörtner and Farrell [1], synergistic effects of elevated temperature and CO2-induced OA on energy metabolism will narrow the thermal tolerance window of marine ectothermal animals. To test this hypothesis, we investigated the effect of an acute temperature rise on energy metabolism of the oyster, Crassostrea gigas chronically exposed to elevated CO2 levels (partial pressure of CO2 in the seawater ~0.15 kPa, seawater pH ~ 7.7). Within one month of incubation at elevated Pco2 and 15 °C hemolymph pH fell (pHe = 7.1 ± 0.2 (CO2-group) vs. 7.6 ± 0.1 (control)) and Peco2 values in hemolymph increased (0.5 ± 0.2 kPa (CO2-group) vs. 0.2 ± 0.04 kPa (control)). Slightly but significantly elevated bicarbonate concentrations in the hemolymph of CO2-incubated oysters ([HCO− 3]e = 1.8 ± 0.3 mM (CO2-group) vs. 1.3 ± 0.1 mM (control)) indicate only minimal regulation of extracellular acid-base status. At the acclimation temperature of 15 °C the OA-induced decrease in pHe did not lead to metabolic depression in oysters as standard metabolism rates (SMR) of CO2-exposed oysters were similar to controls. Upon acute warming SMR rose in both groups, but displayed a stronger increase in the CO2-incubated group. Investigation in isolated gill cells revealed a similar temperaturedependence of respiration between groups. Furthermore, the fraction of cellular energy demand for ion regulation via Na+/K+-ATPase was not affected by chronic hypercapnia or temperature. Metabolic profiling using 1H-NMR spectroscopy revealed substantial changes in some tissues following OA exposure at 15 °C. In mantle tissue alanine and ATP levels decreased significantly whereas an increase in succinate levels was observed in gill tissue. These findings suggest shifts in metabolic pathways following OA-exposure. Our study confirms that OA affects energy metabolism in oysters and suggests that climate change may affect populations of sessile coastal invertebrates such as mollusks

Universal dynamics of rogue waves in a quenched spinor Bose condensate

Universal scaling dynamics of a many-body system far from equilibrium signals the proximity of the time-evolution to a non-thermal fixed point. We find universal dynamics connected with rogue-wave like events in the mutually coupled magnetic components of a spinor gas which propagate in an effectively random potential. The frequency of these caustics is affected by the time varying spatial correlation length of the potential, giving rise to an additional exponent $\delta_\mathrm{c} \simeq 1/3$ for temporal scaling, which is different by a factor $\sim 4/3$ from the exponent $\beta_V \simeq 1/4$ characterizing the scaling of the correlation length $\ell_V \sim t^{\,\beta_V}$ with time. As a result of the caustics, real-time instanton defects appear in the Larmor phase of the spin-1 system as vortices in space and time. The temporal correlations determining the frequency of instanton events to occur scale in time as $t^{\, \delta_\mathrm{I}}$. This suggests that the universality class of a non-thermal fixed point could be characterized by different, mutually related exponents defining the coarsening evolution in time and space, respectively. Our results have a strong relevance for understanding pattern coarsening from first principles and potential implications for dynamics ranging from the early universe to geophysical dynamics and micro physics