Figure 1

Expected tragedy of the commons in an engineered phage system. (A) Extracellular matrix (yellow) impedes phage attachment to the cell surface of its host. Phages are shown as stick figures with gray heads. (B) Exogenous endosialidase enzyme – from any source – augments phage infection by degrading the matrix and enabling phages to access the host surface. (C) The non-engineered (control) phage does not produce endosialidase. (D) The engineered phage produces endosialidase (endosialidase molecules in red; endosialidase phages with a red stripe). (E) Lysis of an infected cell by the control phage. (F) Lysis of an infected cell by the engineered phage releases free endosialidase molecules that degrade the local matrix and diffuse to other cells. (G) The tragedy of the commons. In a mixed environment, endosialidase benefits both types of phages equally, and the control phage numbers should evolve to exceed engineered phage numbers over time because only the engineered phages experience the reproductive cost of producing the enzyme.