Recent advances in the biosynthesis of ω-amino acids and lactams
Increasing petroleum consumption and growing environmental concerns necessitate the sustainable production of chemicals and fuels from renewable resources.By utilizing renewable resources as raw materials and engineered microorganisms as the core tools,the bio-manufacturing of bio-based materials has become a hot research topic due to its green and low-carbon advantages.ω-Amino acids are a type of non-natural amino acids with amino and carboxyl groups located at the ends of the straight carbon chain.Self-cyclization of ω-amino acids produce lactams,which are the key monomers for the synthesis of polyamide materials,commonly known as nylon.Polyamide materials have wide applications and a huge global market over seven million tons per year.Nowadays,polyamide materials and their monomers are primarily produced through petrochemical routes with non-renewable resources.The research on biosynthesis of these materials and monomers is still in the early stages,but significant progress has been made in recent years.This review article systematically introduces the recent advances in the biosynthesis of ω-amino acids and lactams.To achieve the bio-manufacturing of bio-based polyamide materials,researchers have designed artificial biosynthetic pathways for ω-amino acids from renewable carbon sources such as glucose.The key enzymes for the cyclization of ω-amino acids to form lactams have been identified.By assembling the biosynthetic pathway in microbial chassis such as Escherichia coli and Corynebacterium glutamicum,production of ω-amino acids and lactams have been achieved.Furthermore,the metabolic flux was fine-tuned by regulating and optimizing the expression of key genes to improve the biosynthesis of ω-amino acids and lactams.Besides,biosensors of lactams have been developed to transfer the intracellular concentrations of lactams into easily detectable signals such as fluorescence.Such biosensors have been successfully used for high-throughput screening of ω-amino acid cyclization enzymes and dynamic regulation of biosynthetic pathway.These effects have resulted in the successful biosynthesis of C4-C6ω-amino acids and lactams.Particularly,using glucose as a raw material,the production of valerolactam by fed-batch fermentation exceeded 70 g/L,with a productivity of about l g/(L·h),which approaches the level required for industrialization and commercialization.Finally,the review article discusses the current challenges faced in the biosynthesis of ω-amino acids and lactams,including the low yield of biosynthetic pathways,rate-limitations posed by key cyclization enzymes,and insufficient utilization of non-food carbon sources such as one-carbon compounds.
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