Why Be Temperate: Lessons from Bacteriophage λ

Many pathogens have evolved the ability to induce latent infections of their hosts. The bacteriophage lambda is a classical model for exploring the regulation and the evolution of latency. Here, I review recent experimental studies on phage lambda that identify specific conditions promoting the evolution of lysogenic life cycles. In addition, I present specific adaptations of phage lambda that allow this virus to react plastically to variations in the environment and to reactivate its lytic life cycle. All of these different examples are discussed in the light of evolutionary epidemiology theory to disentangle the different evolutionary forces acting on temperate phages. Understanding phage lambda adaptations yield important insights into the evolution of latency in other microbes, including several life threatening human pathogens.