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Laboratory evolution of Jen1p-independent lactate transport in Saccharomyces cerevisiae: identification of ADY2 alleles by whole genome resequencing and mRNA expression analysis

ABSTRACT: Background: Evolutionary engineering is a powerful approach to isolate suppressor mutants and industrially relevant genotypes. Until recently, DNA microarray analysis was the only affordable genome-wide approach to identify the responsible mutations. This situation has changed due to the rapidly decreasing costs of whole genome (re)sequencing. DNA microarray-based mRNA expression analysis and whole genome resequencing were combined in a study on lactate transport in Saccharomyces cerevisiae. Jen1p is the only S. cerevisiae lactate transporter reported in literature. To identify alternative lactate transporters, a jen1Δ strain was evolved for growth on lactate. Results: Two independent evolution experiments yielded Jen1p-independent growth on lactate (μmax 0.14 and 0.18 h-1 for single-cell lines IMW004 and IMW005, respectively). Whereas mRNA expression analysis did not provide leads, whole-genome resequencing showed different single nucleotide changes (C755G/Leu219Val and C655G/Ala252Gly) in the acetate transporter gene ADY2. Analysis of mRNA levels and depth of coverage of DNA sequencing combined with karyotyping, gene deletions and diagnostic PCR showed that in IMW004 an isochromosome III (~475 kb), which contains two additional copies of ADY2C755G, was formed via crossover between YCLWΔ15 and YCRCΔ6. Introduction of the ADY2 alleles in a jen1 ady2 strain resulted in growth on lactate (μmax 0.14 h-1 for Ady2pLeu219Val and 0.12 h-1 for Ady2pAla252Gly). Conclusions: Whole-genome resequencing of yeast strains obtained from independent evolution experiments enabled rapid identification of a key gene that was not identified by mRNA expression analysis of the same strains. Reverse metabolic engineering showed that mutated alleles of ADY2 (C655G and C755G) encode efficient lactate transporters.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE31634 | GEO | 2011/12/21

SECONDARY ACCESSION(S): PRJNA145559

REPOSITORIES: GEO

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Project description:Background: Evolutionary engineering is a powerful approach to isolate suppressor mutants and industrially relevant genotypes. Until recently, DNA microarray analysis was the only affordable genome-wide approach to identify the responsible mutations. This situation has changed due to the rapidly decreasing costs of whole genome (re)sequencing. DNA microarray-based mRNA expression analysis and whole genome resequencing were combined in a study on lactate transport in Saccharomyces cerevisiae. Jen1p is the only S. cerevisiae lactate transporter reported in literature. To identify alternative lactate transporters, a jen1Δ strain was evolved for growth on lactate. Results: Two independent evolution experiments yielded Jen1p-independent growth on lactate (μmax 0.14 and 0.18 h-1 for single-cell lines IMW004 and IMW005, respectively). Whereas mRNA expression analysis did not provide leads, whole-genome resequencing showed different single nucleotide changes (C755G/Leu219Val and C655G/Ala252Gly) in the acetate transporter gene ADY2. Analysis of mRNA levels and depth of coverage of DNA sequencing combined with karyotyping, gene deletions and diagnostic PCR showed that in IMW004 an isochromosome III (~475 kb), which contains two additional copies of ADY2C755G, was formed via crossover between YCLWΔ15 and YCRCΔ6. Introduction of the ADY2 alleles in a jen1 ady2 strain resulted in growth on lactate (μmax 0.14 h-1 for Ady2pLeu219Val and 0.12 h-1 for Ady2pAla252Gly). Conclusions: Whole-genome resequencing of yeast strains obtained from independent evolution experiments enabled rapid identification of a key gene that was not identified by mRNA expression analysis of the same strains. Reverse metabolic engineering showed that mutated alleles of ADY2 (C655G and C755G) encode efficient lactate transporters. The goal of the present study was to investigate whether evolutionary engineering and subsequent elucidation of the underlying mutations can lead to the identification of alternative lactate transporters in S. cerevisiae. Transport of carboxylic acids plays a key role in weak organic acids stress and the responsible membrane transporters are often poorly studied and encoded by multiple redundant genes . Additionally, import of lactate is an essential step in the reutilization of lactate produced during intense exercise in mammals [8]. In S. cerevisiae, Jen1p was previously identified as the only efficient lactate importer by generation of a UV-mutant unable to grow on lactate and subsequent functional complementation with a genomic library . The lactate uptake rate of the resulting jen1 knockout strain was close to the detection limit. Interestingly, export of lactate in engineered lactate producing S. cerevisiae is unaffected by deletion of JEN1 (our unpublished results). These observations suggest the presence of at least one alternative lactate transporter. To test this, a jen1 knockout strain was constructed and evolved for faster growth on lactate as the sole carbon and energy source. The evolved strains were subjected to a combination of mRNA expression analysis and whole genome DNA (re)sequencing to identify the relevant mutations. The resulting leads were tested for lactate transport activity via knockout studies in the evolved strains and reverse engineering of the portable genetic elements into non-evolved strains.

Project description:The organic acids lactate and diacetate are commonly used in combination in ready-to-eat foods because they show synergistic, i.e. greater than additive, ability to inhibit the growth of Listeria monocytogenes. Full genome microarrays were used to investigate the synergistic transcriptomic response of two L. monocytogenes strains, h7858 (serotype 4b) and f6854 (serotype 1/2a), to organic acid, under conditions controlling for osmotic and cold stress. Strains were exposed to BHI broth at 7°C with 4.65% water phase (w.p.) NaCl at pH 6.1 treated with 2% w.p. potassium lactate, 0.14% w.p. sodium diacetate, the combination of both at the same levels, or no inhibitors as control. RNA was extracted 8h after exposure, during lag phase, to capture gene expression changes during adaptation to the organic acid stress. Treatment with organic acids induced massive global transcriptional changes, with 1041 and 640 genes differentially expressed in h7858 and f6854. Major effects of treatment with lactate and diacetate are (i) a total of 474 and 209 genes, for h7858 and f6854, that showed synergistic expression differences, (ii) differential expression of membrane ion transport genes including those encoding ABC transporters of metals and decreased multi-drug transporter expression many ABC, PTS, and drug transporter systems, including increased PTS sugar transport and decreased multi-drug transporter expression, and (iii) altered metabolism including induction of a nutrient limiting stress response, reduction of menaquinone biosynthesis, and a shift from fermentative production of lactate and acetate and lactate to energetically less favorable, neutral acetoin. These data suggest that additional synergies in L. monocytogenes growth inhibition could be achieved by treatments that interfere with cellular energy generation processes. The dye-swapped, single loop design hybridizes a single biological replicate of both 2% water phase lactate (PL) and 0.14% water phase acetate (SDA) treatments to both the control (CTRL) and combination (PLSDA) treatments (4 hybridizations), using opposite dye labels for each sample, and a second biological replicate is hybridized with dye assignments swapped (4 more hybridizations) to balance labeling effects. The design was repeated twice comprising 16 hybridizations over 4 biological replicates for each strain, and 32 total hybridizations over both h7858 and f6854.

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Laboratory evolution of Jen1p-independent lactate transport in Saccharomyces cerevisiae: identification of ADY2 alleles by whole genome resequencing and mRNA expression analysis

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