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

摘要

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 environment