Progress in the metabolic engineering of bio-based lactams and their ω-amino acids precursors

Lactams, cyclic carboxamide acids, are important building blocks as monomers for the manufacture of polyamides (nylons), with a market of millions of tons per year. Likewise, their non-natural building blocks, straight chain ω-amino acids, also have a wide range of applications as pharmaceuticals, therapeutic agents, and precursors to other platform chemicals. Current industrial lactam production requires petrochemically-derived routes that involve the use of harsh chemicals and reaction conditions. Microbial production provides a more sustainable method for production, from cost effective renewable resources. This review provides an extensive overview of progress toward the microbial production of lactams, particularly 4C butyrolactam, 5C valerolactam and 6C caprolactam, and their ω-amino acid precursors. Additionally, recent advances in the field as well as proposed microbial production pathways will be discussed, as well as future perspectives for the production of these important bulk chemicals.