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 ↑Pria1 and U. cynodontis Δfuz7 Δcyp3 PetefmttA ↑Pria1) were applied in itaconate production, obtaining a titer of 56.1 g L−1 and a yield of 0.55 gitaconate per gsubstrate. Both improved titer and yield (increase of 5.2 g L−1 and 0.04 gitaconate per gsubstrate, 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 PetefmttA ↑Pria1. Thereby, an almost doubled itaconate titer of 138 g L−1 was obtained and a yield of 0.62 gitaconate per gsubstrate 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 CO2 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.