High-Yield Biosynthesis of 3-Hydroxypropionic Acid from Acetate by Engineering Bicarbonate Supply and Malonyl-CoA Partitioning in <i>Escherichia coli</i>

3-Hydroxypropionic acid (3-HP) is a versatile platform chemical with broad applications in biodegradable plastics and superabsorbent polymers. Acetate derived from waste biomass and industrial off-gases can serve as a sustainable C2 feedstock for 3-HP production. However, the efficient conversion of acetate to 3-HP remains constrained by insufficient intracellular bicarbonate supply and competition with fatty acid biosynthesis for malonyl-CoA. To address these issues, carboxylation efficiency was enhanced in E. coli by co-expressing carbonic anhydrase (CA) with sodium-dependent bicarbonate transporters (BicA) and supplementation with sodium bicarbonate. Further overexpression of fabF was used to inhibit the initiation of fatty acid biosynthesis, reducing competition for malonyl-CoA. The engineered strain achieved a 3-HP yield of 0.73 g/g in shake flask culture, approaching the theoretical maximum without chemical inhibitors. In a fed-batch bioreactor, the 3-HP titer reached 20.55 g/L with a yield of 0.56 g/g (0.37 mol/mol), corresponding to 74.67% of the theoretical maximum yield. This bioprocess enables efficient valorization of sustainable C2 feedstocks, offering a promising pathway for the industrial production of bio-based platform chemicals.