Enhanced acetic acid stress tolerance and ethanol production in by modulating expression of the de novo purine biosynthesis genes.

BACKGROUND

Yeast 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 , 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.

RESULTS

Three genes involved in de novo purine biosynthesis, namely, , , and , showed significantly increased transcription levels by zinc sulfate supplementation under acetic acid stress, and overexpression of these genes in BY4741 enhanced cell growth under various stress conditions. Meanwhile, ethanol productivity was also improved by overexpression of the three genes under stress conditions, among which the highest improvement attained 158.39% by 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 , 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 genes. Among the changed amino acids, significant increase of the stress protectant γ-aminobutyric acid (GABA) was revealed by overexpression of the genes under acetic acid stress, suggesting that overexpression of the genes exerts control on both purine biosynthesis and amino acid biosynthesis to protect yeast cells against the stress.

CONCLUSION

We 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.