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Microbes are remarkably social. They live in complex, interdependent communities where they share and exchange a variety of beneficial compounds ranging from cell− cell signals to iron-scavenging siderophores to digestive enzymes. Cooperation, particularly between cells of a single genotype (2), is fundamental for how cells survive and grow. However, life is not always so amicable. Microbes are regularly confronted by other genotypes armed to the teeth with weapons including secreted toxins, domesticated viruses, and even poisoned spears. Some microbial toxins have been exploited for decades to produce clinical antibiotics. However, several papers have argued that many antibiotics at their low, ecologically relevant concentrations are, in fact, friendly signals that coordinate community functions (3). A study in PNAS by Abrudan et al.(4) challenges this view, focusing on 13 natural bacterial strains from the …