E. coli microbe seeks out and destroys invaders without harming helpful bacteria. In the war against infection, medicine needs a hero. Meet the bioengineered bacterium that can hunt down pathogens and destroy them with a powerful one–two punch. Synthetic biologist Matthew Chang at Nanyang Technological University in Singapore has armed Escherichia coli bacteria with a ‘seek and kill’ system that targets cells of Pseudomonas aeruginosa, an invasive bacterium that causes pneumonia and other illnesses1. In preliminary tests with infected mice, the modified bacterium left a trail of dead P. aeruginosa in its wake. Chang and his team had previously developed...