Abstract
Yeast cells are challenged by various environmental stresses in the process of industrial fermentation. As the currently main organism for bio-ethanol production, Saccharomyces cerevisiae suffers from ethanol stress. Some amino acids have been reported to be related to yeast tolerance to stresses. Here the relationship between arginine and yeast response to ethanol stress was investigated. Marked inhibitions of ethanol on cell growth, expression of genes involved in arginine biosynthesis and intracellular accumulation of arginine were observed. Furthermore, extracellular addition of arginine can abate the ethanol damage largely. To further confirm the protective effects of arginine on yeast cells, yeast strains with different levels of arginine content were constructed by overexpression of ARG4 involved in arginine biosynthesis or CAR1 encoding arginase. Intracellular arginine was increased by 18.9% or 13.1% respectively by overexpression of ARG4 or disruption of CAR1, which enhanced yeast tolerance to ethanol stress. Moreover, a 41.1% decrease of intracellular arginine was observed in CAR1 overexpressing strain, which made yeast cells keenly sensitive to ethanol. Further investigations indicated that arginine protected yeast cells from ethanol damage by maintaining the integrity of cell wall and cytoplasma membrane, stabilizing the morphology and function of organellae due to low ROS generation.
Highlights
Some amino acids have been reported to contribute to ethanol tolerance
The expression levels of genes involved in arginine metabolism and the intracellular content of arginine were monitored during cell growth in synthetic defined (SD) medium for 18 h
Under non-stressed condition, the expressions of ARG4 encoding argininosuccinase, CPA2 encoding carbamoyl-phosphate synthetase and CAR1 encoding arginase were increased largely from 6 h to 12 h, which was consistent with the rapid cell growth during logarithmic phase
Summary
Some amino acids have been reported to contribute to ethanol tolerance. Deletion of genes involved in tryptophan biosynthesis caused hypersensitivity of yeast cells to ethanol stress, while overexpression of some of those genes or addition of tryptophan to medium increased the ethanol tolerance[5,6,7]. Arginine, which is associated closely with proline metabolism exhibits multiple functions in vitro for its particular chemical structure. It can inhibit heat-induced aggregation of partially folded protein intermediates and suppress protein-protein or protein-surface interactions during protein refolding and purification[13,14,15,16]. An arginase-defective yeast mutant accumulated a higher level of arginine and showed increased leavening ability during the frozen-dough baking process[20]. These results indicated that arginine might have a cryoprotective function in yeast. The underlying possible mechanism for the role of arginine in ethanol tolerance was discussed
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