Box 1. A synthetic predator-prey ecosystem

A synthetic predatorprey ecosystem. (A) The system consists of two types of engineered bacteria controlling each other's survival and death via two different QS signals. Outer boxes represent cell walls. Arrows represent activation or production; blunt arrows represent inhibition or killing. CcdB ('B') is controlled by P_lac/ara-1 in the predator and P_luxI in the prey. CcdA ('A') is controlled by P_luxI. The lux system is shown in blue and the las system in green. The QS genes in the predator are controlled by P_LtetO-1, and those in the prey by P_lac/ara-1. Filled circles represent 3OC6HSL and filled diamonds represent 3OC12HSL. The predatorprey interaction is activated by IPTG. See main text and Supplementary information for more details. (B) Bifurcation analysis of the model in terms of the killing constant d_c (=d_c1 (predator)=d_c2 (prey)) and the growth rate k_c (=k_c1 (predator)=k_c2 (prey)) (left panel). The model construction is described in equations S14S17. A line connecting Hopf bifurcation points demarcates three regions: (i) prey domination, (ii) predatorprey oscillation and (iii) predator domination. Typical population dynamics for specific parameter sets are illustrated for each region (right panel).