Dynamic microbial response under ethanol stress to monitor Saccharomyces cerevisiae activity in different initial physiological states

Dynamic Saccharomyces cerevisiae responses to increasing ethanol stresses were investigated to monitor yeast viability and to optimize bioprocess performance when gradients occurred due to the specific configuration of multi-stage bioreactors with cell recycling or of large volume industrial bioreactors inducing chemical heterogeneities. Twelve fed-batch cultures were carried out with initial ethanol concentrations (P (in)) ranging from 5 g l(-1) to 110 g l(-1) with three different inoculums in different physiological states in terms of viability and quantity of ethanol produced (P (o)). For a given initial cell viability of 50%, the time to reach the maximum growth rate and maximum ethanol production rate was dependent on the difference P (in) - P (o). Whatever the initial physiological state, when the initial ethanol concentration P (in) reached 100 g l(-1), the yeasts died. Experimental results showed that the initial physiological state of the yeast was the major parameter to determine, the microorganisms' capacities to adapt and resist environmental changes.