Roughgarden, J.

A single dynamical equation for the virus to microbe ratio (VMR) shows that an optimal tradeoff occurs between a short lysis time and low burst size vs. a long lysis time and large burst size. The model predicts that interventions lowering phage adsorption by killing free virus and/or limiting their access to bacteria cause the evolution of an increased lysis time and higher burst size 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 an intervention that lowers bacterial growth, R, induces the prophages within it to switch to their lytic phase. An intervention that simultaneously lowers both viral accessibility to bacteria and bacterial growth rate may increase the net virus to bacterial ratio (VMR), a result reminiscent of the Volterra principle for predator-prey dynamics in ecology.