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Tryptophan plays a central role in yeast’s tolerance to isobutanol

ABSTRACT: Isobutanol is considered a potential biofuel and can be produced by genetically modified microorganisms. Saccharomyces cerevisiae inherently produces isobutanol through valine intermediate(s), so it serves as a good host. However, isobutanol's toxicity remains a key obstacle for bioproduction. In our study, we first used image recognition to screen the colony growth of a yeast gene deletion library and inferred that genes involved in tryptophan biosynthesis, ubiquitination, and the pentose phosphate pathway (PPP) contribute to isobutanol tolerance. The importance of tryptophan in yeast's tolerance to isobutanol was confirmed by the recovery of isobutanol tolerance in a tryptophan biosynthesis defective strain by adding exogenous tryptophan. Transcriptomic analysis revealed that amino acid biosynthesis- and transportation-related genes in a tryptophan biosynthesis defective host were up regulated under conditions such as nitrogen starvation. This may explain why ubiquitination for protein degradation was involved for the protein turnover. PPP metabolites and vitamin B1/B6 may serve as precursors and cofactors in tryptophan biosynthesis to enhance isobutanol tolerance. Furthermore, the tolerance mechanism may also be linked to tryptophan metabolism, including the kynurenine pathway and nicotinamide adenine dinucleotide biosynthesis. Both pathways are responsible for cellular redox balance and antioxidative ability and figured out that tryptophan may play a crucial role on isobutanol tolerance. Our study highlights the central role of tryptophan in yeast's isobutanol tolerance and offers new clues for engineering a yeast host with strong isobutanol tolerance.

ORGANISM(S): Saccharomyces cerevisiae S288C

PROVIDER: GSE175794 | GEO | 2021/10/20

REPOSITORIES: GEO

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Project description:BACKGROUND:Isobutanol is a promising next generation biofuel with demonstrated high yield microbial production, but the toxicity of this molecule reduces fermentation volumetric productivity and final titers. Organic solvent tolerance is a complex, multigenic phenotype that has been recalcitrant to rational engineering approaches. We apply experimental evolution followed by genome resequencing and a gene expression study to elucidate genetic bases on adaptation to exogenous isobutanol stress. RESULTS:The adaptations acquired in our evolved lineages exhibit antagonistic pleiotropy between minimal and rich medium, and appear to be specific to the effects of longer chain alcohols. By examining genotypic adaptation in multiple independent lineages, we find evidence of parallel evolution in hfq, mdh, acrAB, gatYZABCD, and rph genes. Many isobutanol tolerant lineages show reduced rpoS activity, perhaps related to mutations in hfq or acrAB. Consistent with the complex, multigenic nature of solvent tolerance, we observe adaptations in a diversity of cellular processes. Many adaptations appear to involve epistasis between different mutations, implying a rugged fitness landscape for isobutanol tolerance. We observe a trend of evolution targeting post-transcriptional regulation and high centrality nodes of biochemical networks. Collectively, the genotypic adaptations we observe suggest mechanisms of adaptation to isobutanol stress based on remodelling the cell envelope and surprisingly, stress response attenuation. CONCLUSIONS:We have discovered a set of genotypic adaptations that confer increased tolerance to exogenous isobutanol stress. Our results are immediately useful to efforts to engineer more isobutanol tolerant host strains of E. coli for isobutanol production. We suggest that rpoS and post-transcriptional regulators, such as hfq, RNA helicases, and sRNAs may be interesting mutagenesis targets for futurue global phenotype engineering. Two strains (WT strain and G3.2 mutant strain), each with two culture conditions (with and without isobutanol in medium). Three biological replicates for each strain/culture condition. Twelve samples in total.

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Tryptophan plays a central role in yeast’s tolerance to isobutanol

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