Engineered Gene Circuits: From Clocks to Synchronized Delivery

Intracellular variability is a major obstacle to the fidelity required for a genetic circuit to execute a series of "pre-programmed" instructions. Over the past five years we have explored how determinism can arise from the synchronization of a large number of cells; in other words, synchronize gene circuits operating in individual cells and view the colony as the primary design element. We are currently using our understanding of these processes to engineer bacteria for the safe production and delivery of anti-tumor toxins. The long-held monolithic view of bacteria as pathogens has given way to an appreciation of the widespread prevalence of functional microbes within the human body. Given this vast milieu, it is perhaps inevitable that certain bacteria would evolve to preferentially grow in environments that harbor disease and thus provide a natural platform for the development of engineered therapies. We have engineered a clinically relevant bacterium to lyse synchronously at a threshold population density and to release genetically encoded cargo. Following quorum lysis, a small number of surviving bacteria reseed the growing population, thus leading to pulsatile de- livery cycles. Working with Sangeeta Bhatia (MIT) and Tal Danino (Columbia), we have begun to demonstrate the therapeutic potential of the bacteria in animal models using luciferase to monitor in vivo bacterial population dynamics. This work represents our early progress in transversing the scales of Synthetic Biology from the level of mathematically designed circuitry to therapeutically relevant animal models.