Abstract
In recent years, it was shown that itaconic acid can be produced from glucose with Ustilago strains at up to maximum theoretical yield. The use of acetate and formate as co-feedstocks can boost the efficiency of itaconate production with Ustilaginaceae wild-type strains by reducing the glucose amount and thus the agricultural land required for the biotechnological production of this chemical. Metabolically engineered strains (U. cynodontis Δfuz7 Δcyp3 ↑P(ria1) and U. cynodontis Δfuz7 Δcyp3 P(etef)mttA ↑P(ria1)) were applied in itaconate production, obtaining a titer of 56.1 g L(-1) and a yield of 0.55 g(itaconate) per g(substrate). Both improved titer and yield (increase of 5.2 g L(-1) and 0.04 g(itaconate) per g(substrate), respectively) were achieved when using sodium formate as an auxiliary substrate. By applying the design-of-experiments (DoE) methodology, cultivation parameters (glucose, sodium formate and ammonium chloride concentrations) were optimized, resulting in two empirical models predicting itaconate titer and yield for U. cynodontis Δfuz7 Δcyp3 P(etef)mttA ↑P(ria1). Thereby, an almost doubled itaconate titer of 138 g L(-1) was obtained and a yield of 0.62 g(itaconate) per g(substrate) was reached during confirmation experiments corresponding to 86% of the theoretical maximum. In order to close the carbon cycle by production of the co-feed via a "power-to-X" route, the biphasic Ru-catalysed hydrogenation of CO(2) to formate could be integrated into the bioprocess directly using the obtained aqueous solution of formates as co-feedstock without any purification steps, demonstrating the (bio)compatibility of the two processes.