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Carbon Flux Trapping: Highly Efficient Production of Polymer‐Grade d‐Lactic Acid with a Thermophilic d‐Lactate Dehydrogenase

High production of polymer‐grade d‐lactic acid is urgently required, particularly for the synthesis of polylactic acid. High‐temperature fermentation has multiple advantages, such as lower equipment requirement and energy consumption, which are essential for lowering operating costs. We identified and introduced a unique d‐lactate dehydrogenase into a thermotolerant butane‐2,3‐diol‐producing strain. Carbon flux “trapping” was achieved by a “trapping point” created by combination of the introduced enzyme and the host efflux pump, which afforded irreversible transport of d‐lactic acid. The overall carbon flux of the engineered strain was significantly enhanced and was redistributed predominantly to d‐lactic acid. Under optimized conditions at 50 °C, d‐lactic acid reached the highest titer (226.6 g L−1) reported to date. This discovery allows us to extend the carbon flux trapping strategy to engineering complex metabolic networks.