Effect of changing environmental conditions on the fermentative growth of Saccharomyces cerevisiae S288C: Auxo-accelerostat study
Year: 2006
Type: article
Abstract: The technological processes of ethanol, wine, beer and bread production all rely on fermentative growth of Saccharomyces cerevisiae.The effect of environmental conditions on the fermentative growth of yeasts, essential for optimisation of the process, has been studied mostly in batch and/or anaerobic chemostat cultures.In this study a novel auxostat based cultivation technique, auxo-accelerostat, was developed and used to map the effect of smoothly changing environmental conditions on the fermentative growth and metabolic activity of S. cerevisiae S288C.Various environmental factors (pH, pO 2 , temperature, salinity, concentration of ethanol, propanol, tryptone, yeast extract and aliphatic monocarboxylic acids) were studied.The effect of the rate of change of the environmental parameters on the growth of yeasts was clearly demonstrated in auxo-accelerostat experiments with increasing the concentration of monocarboxylic acids: it was shown that the toxic effect depends not only on the nature of the monocarboxylic acid but also on the rate of addition of this acid into the culture medium.A slow decrease in the culture pH and dissolved oxygen concentration below the optimum values or increase in monocarboxylic acid concentration in the culture medium caused a decrease in growth rate mainly due to the increase in the energy costs for maintaining homeostasis and not by the inhibition of the energy producing reactions.A slow increase in the concentration of biomass, propanol and NaCl as well as a fast increase in monocarboxylic acids lead to a decrease in glycolytic activity (Q ATP ).Auxo-accelerostat experiments showed that in optimal conditions in mineral medium with excess of glucose (introducing fermentative mode of growth), the capacity of ATP production was not obviously a growth rate-limiting step for S. cerevisiae and glycolytic activity was controlled by the demand for ATP.This assumption was supported by the fact that slow addition of monocarboxylic acids to the culture medium was accompanied by up to 80% increase in the specific ATP production rate, i.e. the cells were able to increase the energy production as a response to a rise in maintenance costs.Moreover, as the slow addition of tryptone or yeast extract into the culture medium (providing the precursors) increased the specific growth rate, it could be assumed that the growth rate limiting step for yeast cells at fermentative growth is the synthesis of monomers (e.g., amino acids, nucleotides) and their polymerisation.The present study demonstrates that the auxo-accelerostat cultivation method, besides being an efficient tool for the quantification of culture characteristics, is also a promising method allowing elucidation of the growth rate control mechanism(s) in cells.
Source: TUTL Collection
Author: Kasemets, Kaja
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W6981313456