Auxotrophic Mutations Reduce Tolerance of Saccharomyces cerevisiae to Very High Levels of Ethanol Stress

Abstract

Very high ethanol tolerance is a distinctive trait of the yeast Saccharomyces cerevisiae with notable ecological and industrial importance. Although many genes have been shown to be required for moderate ethanol tolerance (i.e., 6 to 12%) in laboratory strains, little is known of the much higher ethanol tolerance (i.e., 16 to 20%) in natural and industrial strains. We have analyzed the genetic basis of very high ethanol tolerance in a Brazilian bioethanol production strain by genetic mapping with laboratory strains containing artificially inserted oligonucleotide markers. The first locus contained the ura3⌬0 mutation of the laboratory strain as the causative mutation. Analysis of other auxotrophies also revealed significant linkage for LYS2, LEU2, HIS3, and MET15. Tolerance to only very high ethanol concentrations was reduced by auxotrophies, while the effect was reversed at lower concentrations. Evaluation of other stress conditions showed that the link with auxotrophy is dependent on the type of stress and the type of auxotrophy. When the concentration of the auxotrophic nutrient is close to that limiting growth, more stress factors can inhibit growth of an auxotrophic strain. We show that very high ethanol concentrations inhibit the uptake of leucine more than that of uracil, but the 500-fold-lower uracil uptake activity may explain the strong linkage between uracil auxotrophy and ethanol sensitivity compared to leucine auxotrophy. Since very high concentrations of ethanol inhibit the uptake of auxotrophic nutrients, the active uptake of scarce nutrients may be a major limiting factor for growth under conditions of ethanol stress.

Polygenic analysis of very high acetic acid tolerance in the yeast Saccharomyces cerevisiae reveals a complex genetic background and several new causative alleles

“…It was also reported that heterozygous deletion of MET4 caused hypersensitivity to H 2 O 2 and decreased oxidative stress resistance [88]. In addition, the presence of auxotrophic mutations has been linked to reduced stress tolerance in yeast [89,90].…”

In depth understanding the molecular response to the enhanced secretion of fatty acids in S accharomyces cerevisiae due to one-step gene deletion of acyl-CoA synthetases

“…While nutritional supplementation may differ from genetic complementation, the difference could be minimal when YB526 and YB332 were cultured in the complex media under the same conditions. Previous reports suggested that the great differences between the prototrophic and auxotrophic strains could be led to only by severe nutrient starvation or very high levels of ethanol stress (16-20%) [36,37]. And two major responses from the nutrient starvation were demonstrated previously as follows: (1) down-regulation of processes linked to cell growth and catabolism and (2) activation of carbon or nitrogen metabolic pathways for the supply of auxotrophically required compound [37].…”

Two FgLEU2 Genes with Different Roles in Leucine Biosynthesis and Infection-Related Morphogenesis in Fusarium graminearum

“…cerevisiae , functional analysis showed that disruption of LEU2 resulted in Leu-auxotroph and decreased resistance to acetic acid and to very high levels of ethanol stress of the mutants [7]. Very few documents characterized functions of LEU2 in filamentous fungi except for a relatively ancient and primary research in Aspergillus niger showed that this fungus elaborates two isoenzymes of IPMD and these two encoding genes were differentially expressed [8].…”