Evolutionarily Optimal Phage Life-History Traits: Burst Size vs. Lysis Time

A model based on a dynamical equation for the virus-to-microbe ratio (VMR) during log phase population growth shows that an optimal balance occurs between a short lysis time with low burst size vs. a long lysis time with large burst size. The model predicts that interventions lowering phage adsorption by killing free virus and/or limiting their access to bacteria favors the evolution of an increased lysis time and higher burst per infecting microbe until the intervention either drives a virulent phage extinct or, for temperate phage, drives the phage from its lytic phase into its lysogenic phase. The model also predicts that along an environmental gradient of increasing primary productivity the optimal lysis time shortens along the gradient, implying that the lytic life cycle goes around faster along the gradient.