Sustainable Bioproduction of 3-Hydroxypropionic Acid from Acetic Acid by Engineering Malonate Semialdehyde Metabolism in Pseudomonas denitrificans

3-Hydroxypropionic acid (3-HP) is a valuable platform chemical used in the production of biodegradable plastics, acrylic acid, and other industrial chemicals. Developing a sustainable, high-yield microbial process is essential to replace petrochemical-based synthesis. This study advances 3-HP bioproduction using acetic acid, a renewable feedstock obtainable from lignocellulosic biomass, organic waste streams, and C1 gases, providing a sustainable alternative to sugar-based fermentation. However, the accumulation and degradation of malonate semialdehyde (MSA), a toxic intermediate in the malonyl-CoA pathway, limit 3-HP production. To address this, we engineered Pseudomonas denitrificans by identifying and deleting key MSA catabolic genes (mmsAI, mmsAII, mmsAIII, and BAPAT), redirecting carbon flux toward 3-HP synthesis. Further optimization via 5′-UTR engineering and fed-batch fermentation with pH-stat control resulted in the highest reported 3-HP titer from waste-derivable acetate, reaching 31.2 g/L in 48 h with a peak productivity of 1.02 g/L/h. This work establishes a scalable, eco-friendly bioprocess for producing biobased chemicals from nonfood carbon sources, advancing green chemistry and circular bioeconomy principles.