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

Abstract A new 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. Importance A new approach to modeling phage life history predicts that virus respond to interventions that limit their adsorption onto bacteria by evolving a longer lysis time. The new model also predicts that lysis time of virus in nature shortens and the virus life cycle goes around faster as environmental conditions favoring virus production increase. These predictions show that virus life-history traits are not arbitrary and can be predicted in advance based on environmental conditions. Competing Interest Statement The authors have declared no competing interest. Footnotes Editorial changes: section added describing reasons for adopting new model of phage/bacteria model instead of using classical Campbell model and its derivatives, paragraphs added to defend simplifying assumptions in mold and indicated where additions could be made if necessary, added section in beginning describing paper's importance, did some miscellaneous wordsmithing and added a few references, no changes made to formulas or figures.