Alternative malonyl-CoA pathways for microbial production of diverse products

Malonyl-CoA serves as a central precursor for the biosynthesis of diverse high-value compounds, including lipids, organic acids, and polyketides, in engineered microbial fermentation systems. However, insufficient malonyl-CoA supply often limits the production of these products. Intracellular malonyl-CoA levels are tightly regulated by the activities of acetyl-CoA carboxylase (ACC) and fatty acid synthesis pathway enzymes. Although strategies have been developed to redirect malonyl-CoA flux from fatty acid biosynthesis toward desired products, native ACC-mediated synthesis remains constrained by slow kinetics, complex regulation, and ATP consumption. To overcome these limitations, two alternative malonyl-CoA biosynthetic pathways have recently been developed. The malonate assimilation pathway enables direct uptake and CoA ligation of exogenous malonate, providing precise control over malonyl-CoA metabolism. The non-carboxylative malonyl-CoA (NCM) pathway converts pyruvate to malonyl-CoA through a novel intermediate, eliminating both ATP and CO₂ loss while simultaneously regenerating NADPH. This review highlights recent advances in these two alternative malonyl-CoA biosynthetic pathways and their applications across diverse microbial hosts, underscoring their potential to enhance the sustainable production of valuable biochemicals.