Abstract
Ustilago maydis, a member of the Ustilaginaceae family, is a promising host for the production of several metabolites including itaconic acid. This dicarboxylate has great potential as a bio-based building block in the polymer industry, and is of special interest for pharmaceutical applications. Several itaconate overproducing Ustilago strains have been generated by metabolic and morphology engineering. This yielded stabilized unicellular morphology through fuz7 deletion, reduction of by-product formation through deletion of genes responsible for itaconate oxidation and (glyco)lipid production, and the overexpression of the regulator of the itaconate cluster ria1 and the mitochondrial tricarboxylate transporter encoded by mttA from Aspergillus terreus. In this study, itaconate production was further optimized by consolidating these different optimizations into one strain. The combined modifications resulted in itaconic acid production at theoretical maximal yield, which was achieved under biotechnologically relevant fed-batch fermentations with continuous feed.
Highlights
Itaconic acid and its derivatives are found in many application fields, such as the production of paper, paints, and fibers, or in waste water treatment [1,2,3,4] providing a stable market for this bio-based chemical
Itaconate was produced from glucose at 100% of the theoretical maximum yield during the production phase in a low-density fermentation
Looking forward, osmotolerance of U. maydis may be enhanced by laboratory evolution
Summary
Itaconic acid and its derivatives are found in many application fields, such as the production of paper, paints, and fibers, or in waste water treatment [1,2,3,4] providing a stable market for this bio-based chemical. U. maydis produces itaconate as one product from a potpourri of metabolites including organic acids such as malate, succinate, and (S)-2-hydroxyparaconate, polyols such as erythritol and mannitol, and different lipidic products including glycolipids and triglycerides [28,29,30,31,32,33] It can metabolize a range of renewable carbon sources, which besides sugar include glycerol [34], galacturonic acid [35], cellulose [36], xylan [37], and pectin [38]. In previous studies several knockouts, promotor replacements and overexpression of genes were implemented to increase itaconate production, reduce by-product formation, and stabilize the unicellular morphology [10,26,41,44,45] Those metabolic engineering approaches resulted in several itaconate hyper-producing Ustilago strains with individual modifications. The catalytic vigor of the strain was demonstrated in fed-batch cultures
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