Feedforward growth rate control mitigates gene activation burden

Heterologous gene activation causes non-physiological burden on cellular resources that cells are unable to adjust to. Here, we introduce a feedforward controller that actuates growth rate upon activation of a gene of interest (GOI) to compensate for such a burden. The controller achieves this by activating a modified SpoT enzyme (SpoTH) with sole hydrolysis activity, which lowers ppGpp level and thus increases growth rate. An inducible RelA+ expression cassette further allows to precisely set the basal level of ppGpp, and thus nominal growth rate, in any bacterial strain. Without the controller, activation of the GOI decreased growth rate by more than 50%. With the controller, we could activate the GOI to the same level without growth rate defect. A cell strain armed with the controller in co-culture enabled persistent population-level activation of a GOI, which could not be achieved by a strain devoid of the controller. The feedforward controller is a tunable, modular, and portable tool that allows dynamic gene activation without growth rate defects for bacterial synthetic biology applications. Heterologous gene activation causes non-physiological burden on cellular resources that cells are unable to adjust to. Here the authors present a tunable, modular, and portable feedforward controller that allows dynamic modulation of a genes expression to possibly high-levels without substantially affecting growth rate.

Automated summary

Heterologous gene activation puts a burden on cellular resources, but researchers have developed a feedforward controller that can compensate for this burden by adjusting the growth rate. The controller activates a modified enzyme that lowers ppGpp level, thereby increasing growth rate. This controller allows dynamic gene activation without affecting the growth rate, making it a useful tool for bacterial synthetic biology applications.