Improved Itaconate Production with Ustilago cynodontis via Co-Metabolism of CO 2 -Derived Formate.

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 Δ fuz7 Δ cyp3 ↑P ria1 and U. cynodontis Δ fuz7 Δ cyp3 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 Δ fuz7 Δ cyp3 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.