Rock-paper-scissors: Engineered population dynamics increase genetic stability

Stabilizing synthetic gene circuits Making synthetic gene circuits in bacteria is one thing, but making them stable under selective pressure with high mutation rates is another. Liao et al. addressed this problem with an ecological strategy in which they created three strains of bacteria, each of which could kill or be killed by one of the other strains (see the Perspective by Johnston and Collins). Once the first strain of bacteria hosting the engineered circuit underwent mutations that decreased function, the system could be “rebooted” by addition of another strain that killed the first but also contained the desired synthetic circuit, allowing its function to proceed unperturbed. This strategy provides a way to control synthetic ecosystems and maintain synthetic gene circuits without using traditional selection to maintain plasmids with antibiotics. Science , this issue p. 1045 ; see also p. 986