Conversion of CO into organic acids by engineered autotrophic yeast.

The increase of CO emissions due to human activity is one of the preeminent reasons for the present climate crisis. In addition, considering the increasing demand for renewable resources, the upcycling of CO as a feedstock gains an extensive importance to establish CO-neutral or CO-negative industrial processes independent of agricultural resources. Here we assess whether synthetic autotrophic () can be used as a platform for value-added chemicals using CO as a feedstock by integrating the heterologous genes for lactic and itaconic acid synthesis. C labeling experiments proved that the resulting strains are able to produce organic acids via the assimilation of CO as a sole carbon source. Further engineering attempts to prevent the lactic acid consumption increased the titers to 600 mg L, while balancing the expression of key genes and modifying screening conditions led to 2 g L itaconic acid. Bioreactor cultivations suggest that a fine-tuning on CO uptake and oxygen demand of the cells is essential to reach a higher productivity. We believe that through further metabolic and process engineering, the resulting engineered strain can become a promising host for the production of value-added bulk chemicals by microbial assimilation of CO, to support sustainability of industrial bioprocesses.