Mechanisms of formic acid stress response in evolved yeast for microbial-electrocatalytic systems.

Integrated electrocatalytic microbial systems (iEMS) offers a sustainable route for carbon cycling. However, formic acid by-product stress severely hinders microbial conversion. Herein, we reveal the adaptive mechanisms of Saccharomyces cerevisiae under formic acid stress during ethanol cultivation through adaptive laboratory evolution and transcriptomic analysis. Formic acid exposure systematically downregulates central carbon metabolism while upregulating the acetaldehyde branch to replenish carbon skeletons. Concurrently, cell cycle genes are activated via MAPK signaling, and ribosomal biogenesis is enhanced to bolster stress-response translation. By improving the formic acid tolerance of Saccharomyces cerevisiae and investigating the underlying mechanisms, we engineered yeast to produce 3-hydroxypropionic acid (3-HP) from ethanol. Finally, we integrated an upstream electrocatalytic system with a downstream engineered yeast producing 3-HP, achieving a titer of 95.8 mg/L, which is 4-fold higher than that of the initial strain. This work elucidates the molecular basis of formic acid tolerance and demonstrates a viable route for iEMS.