Metabolic engineering of Escherichia coli for the high-level production of putrescine

Putrescine is an important platform chemical used in the manufacture of engineering plastics. To support the development of a sustainable plastics industry, microbial production of putrescine from renewable resources has attracted increasing attention. In this study, we report the development of an engineered Escherichia coli strain capable of efficiently producing putrescine. To overcome the limitation caused by putrescine toxicity, the previously developed XQ52 strain (a W3110-derived putrescine-producing strain) was subjected to adaptive laboratory evolution, resulting in the AXQ52 strain, which produced 61.7 g/L of putrescine in fed-batch fermentation. This titer surpassed the natural tolerance threshold of E. coli. Genome sequencing of the AXQ52 strain revealed mutations that improved cellular fitness under high putrescine concentrations. Further production improvements were achieved by fine-tuning the expression of phosphoenolpyruvate carboxylase gene, introducing a heterologous ornithine acetyltransferase, and disrupting glutamate decarboxylase. The final engineered strain produced 72.7 g/L of putrescine with a yield of 0.25 g/g glucose and a productivity of 1.28 g/L/h, representing the highest microbial putrescine production reported to date from a simple carbon source.