Metabolic control engineering: A novel method for enhancing production in Escherichia coli

Metabolic engineering has achieved encouraging success in producing heterologous metabolites in foreign hosts. However, engineered metabolic pathways, typically uncontrolled or deregulated, are often detrimental to cell growth because of metabolic imbalance, which causes suboptimal productivity. Here we demonstrated that incorporating a regulatory circuit, in addition to amplifying the pathway genes, is an effective way for improving productivity. In particular, we recruited and altered one of the global regulatory systems in Escherichia coli, the Ntr regulon, to control the engineered lycopene biosynthesis pathway. The altered regulon, stimulated by excess glycolytic flux though sensing of the acetyl phosphate level, has been used to control the expression of key enzymes involved with carotenoid and aromatics synthesis in response to flux dynamics. In particular, we showed that this artificial regulon was able to significantly enhance lycopene production and reduce the growth retardation caused by metabolic imbalance. Additionally, we explored other applications that took advantage of the altered regulon's ability to sense and respond to acetyl phosphate. Efforts were made to engineer glnAp2, a key promoter in the Ntr regulon, for use as a strong and controllable expression promoter and the potential development of an acetyl phosphate metabolic sensor was considered.