When cyanophage infect Prochlorococcus, they kill some host bacteria but remodel others in ways that makes the survivors hardier, according to Sallie Chisholm of Massachusetts Institute of Technology (MIT) in Cambridge, Mass., Debbie Lindell of the Technion Israel Institute of Technology (TIIT) in Technion City, Haifa, Israel, and their collaborators. Their analysis of the seesaw genetic relationship between this phage and its ocean-dwelling photosynthetic bacterial host, which lies at the base of the sea food chain and produces much of the oxygen we breathe, appears in the September 6 issue of Nature.