Engineering an Overflow-Responsive Regulation System for Balancing Cellular Redox and Optimizing Microbial Production

Escherichia coli accumulates acetate as a byproduct in fast growth aerobic conditions when using glucose as carbon source. This phenomenon, known as overflow metabolism, has negative impacts on cell growth and protein expression, also causes carbon loss during biosynthesis in most microbial production scenarios. In this study, we regarded the "waste" metabolite as a useful metabolism indicator, constructed an overflow biosensor to monitor the change of acetate concentration and converted the signal into various regulation outputs. Phloroglucinol is a phenolic compound with several derivatives that exhibit various pharmacological activities. By applying the bifunctional dynamic regulation system on the phloroglucinol production, we released the cellular redox pressure in real-time and reduced the waste of carbon flux on overflow metabolism. Finally, carbon flux was redirected more favorably towards the desired product, resulting in a boosted phloroglucinol titer of 1.30 g/L, increased by 2.04-fold. Overall, this study explored the use of a central byproduct-responsive biosensor system on improving cellular metabolic status, providing a general approach for enhancing bioproduction.