Control of Hidden Interactions and Competition between Synthetic Gene Circuits and Host Cell

Failure of modularity remains a significant challenge for assembling synthetic gene circuits with tested modules as they often do not function as expected. Hidden circuit-host interactions, such as growth feedback and resource competition, could significantly impair intended circuit function but are often neglected. Our first work revealed a topology-dependent interference of synthetic gene circuit function by growth feedback. Specifically, the memory of the self-activation switch is quickly lost due to the growth-mediated dilution of the circuit products. Decoupling of growth feedback reveals its memory, manifested by its hysteresis property across a broad range of inducer concentration. On the contrary, the toggle switch is more refractory to growth-mediated dilution and can retrieve its memory after the fast-growth phase. Recently, we studied how nutrient level modulates growth feedback and circuit functions and found an unexpected oscillation behavior of a bistable switch circuit. In another work, we unveiled a winner-takes-all resource competition that redirected desired successive cell fate transitions as designed with synthetic cascading bistable switches (Syn-CBS) circuit. We decoupled the resource competition with a division of labor strategy by constructing a two-strain circuit, which achieved successive activation and stable coactivation of the two switches. More recently, we proposed a shared and tunable system of negatively competitive regulation (NCR) and demonstrated NCR significantly increases control efficacy over widely-used global and local negative feedback controllers.