Abstract
BackgroundYeast strains that are tolerant to multiple environmental stresses are highly desired for various industrial applications. Despite great efforts in identifying key genes involved in stress tolerance of budding yeast Saccharomyces cerevisiae, the effects of de novo purine biosynthesis genes on yeast stress tolerance are still not well explored. Our previous studies showed that zinc sulfate addition improved yeast acetic acid tolerance, and key genes involved in yeast stress tolerance were further investigated in this study.ResultsThree genes involved in de novo purine biosynthesis, namely, ADE1, ADE13, and ADE17, showed significantly increased transcription levels by zinc sulfate supplementation under acetic acid stress, and overexpression of these genes in S. cerevisiae BY4741 enhanced cell growth under various stress conditions. Meanwhile, ethanol productivity was also improved by overexpression of the three ADE genes under stress conditions, among which the highest improvement attained 158.39% by ADE17 overexpression in the presence of inhibitor mixtures derived from lignocellulosic biomass. Elevated levels of adenine-nucleotide pool “AXP” ([ATP] + [ADP] + [AMP]) and ATP content were observed by overexpression of ADE17, both under control condition and under acetic acid stress, and is consistent with the better growth of the recombinant yeast strain. The global intracellular amino acid profiles were also changed by overexpression of the ADE genes. Among the changed amino acids, significant increase of the stress protectant γ-aminobutyric acid (GABA) was revealed by overexpression of the ADE genes under acetic acid stress, suggesting that overexpression of the ADE genes exerts control on both purine biosynthesis and amino acid biosynthesis to protect yeast cells against the stress.ConclusionWe proved that the de novo purine biosynthesis genes are useful targets for metabolic engineering of yeast stress tolerance. The engineered strains developed in this study with improved tolerance against multiple inhibitors can be employed for efficient lignocellulosic biorefinery to produce biofuels and biochemicals.
Highlights
Yeast strains that are tolerant to multiple environmental stresses are highly desired for various industrial applications
Transcriptome analyses revealed remodeling of purine metabolism upon zinc sulfate supplementation in the presence of acetic acid In our previous studies, global gene transcription of the flocculating yeast SPSC01 under acetic acid stress with and without zinc sulfate supplementation was compared when cells were collected at the same timepoint (72 h after inoculation) [17]; the growth states of the strains were different at the same timepoint
To further investigate the roles of these genes in yeast stress tolerance, the three ADEnine requiring (ADE) genes were overexpressed in S. cerevisiae BY4741, and the recombinant strains were named BADE1, BADE13, and BADE17, respectively
Summary
Yeast strains that are tolerant to multiple environmental stresses are highly desired for various industrial applications. Studies on the underlying mechanisms of yeast stress tolerance and strategies to develop robust strains that are tolerant to various stresses have received continuous attention [2,3,4,5,6,7]. Lignocellulosic biomass, such as agricultural and forest residues, is abundant in nature, and is widely studied as promising renewable feedstocks to produce biofuels and biochemicals [2, 3]. Development of robust yeast strains that are tolerant to various stress conditions is highly desired for lignocellulosic biorefinery
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