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Model-guided development of evolutionarily stable yeast chassis for dicarboxylic acids production

ABSTRACT:

Chassis strain suitable for producing multiple compounds is a central concept in synthetic biology. Design of a chassis using computational, first-principle, models is particularly attractive due to the predictability and control it offers, including against phenotype reversal due to adaptive mutations. Yet, the theory of model-based chassis design has rarely been put to rigorous experimental test and assessed at multiomics level. Here, we report two Saccharomyces cerevisiae chassis strains for dicarboxylic acid production based on genome-scale metabolic modelling. The chassis strain, harbouring gene knockouts in serine biosynthesis and in pentose-phosphate pathway, is geared for higher flux towards three target products - succinate, fumarate and malate - but does not appreciably secrete any. Introducing modular product-specific mutations resulted in improved secretion of the corresponding acid as predicted by the model. Adaptive laboratory evolution of the chassis-derived producer cells further improved production for succinate and fumarate attesting to the evolutionary robustness of the underlying growth-product coupling. In the case of malate, which exhibited decreased production during evolution, the multiomics analysis revealed flux bypass at peroxisomal malate dehydrogenase that was not accounted in the model. Integration of transcriptomics, proteomics and metabolomics data showed overall concordance with the flux re-routing predicted by the model. Together, our results provide experimental evidence for model-based design of microbial chassis and have implications for computer-aided design of microbial cell factories.

INSTRUMENT(S): Gas Chromatography MS -

SUBMITTER: Filipa Pereira

PROVIDER: MTBLS2007 | MetaboLights | 2021-07-19

REPOSITORIES: MetaboLights

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Project description:Malic enzymes decarboxylate the tricarboxylic acid (TCA) cycle intermediate malate to the glycolytic end-product pyruvate and are well positioned to regulate metabolic flux in central carbon metabolism. The bacterium Sinorhizobium meliloti has a NAD(P)-malic enzyme (DME) and a NADP-malic enzyme (TME) and DME is required for symbiotic N2-fixation. To help understand the role of these enzymes, we examined growth, metabolic and transcriptional consequences resulting from the deletion of these enzymes. Few effects were observed upon growth with glucose, whereas growth with the gluconeogenic substrate, succinate, resulted in transcriptional and metabolic effects particularly in the dme mutant strains. When grown with succinate, DME mutant cells accumulated hexose sugar phosphates and trehalose, while TME mutants accumulated putrescine. Succinate-grown DME mutant cells also showed increased transcription of genes for gluconeogenesis and for pathways such as amino acid and fatty acid synthesis that divert metabolites away from the TCA cycle. These data suggested that, DME is required to regulate the levels of TCA cycle intermediates and that the activity of TME is insufficient to prevent the accumulation of TCA cycle intermediates in cells utilizing succinate as carbon source. Consistent with this, in short-1-3 hour incubations with succinate, dme mutant cells excreted large amounts of malate whereas little malate was excreted from tme or wild-type cells. These results support the suggestion that DME is required for N2-fixation in alfalfa because it is required for synthesis of pyruvate and acetyl-CoA and the rapid metabolism of C4-dicarboxylates supplied by the plant. RNA expression was measured for S. meliloti in exponential phase grown in MOPS (morpholinpropanesulfonic acid) buffered minimal media under 2 growth conditions: 1) 15 mM succinate, 2) 15 mM glucose; using wild type cells as well as dme and tme mutant strains (6 experiments, 2 replicates: total 12 samples)

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Model-guided development of evolutionarily stable yeast chassis for dicarboxylic acids production

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