Figure 1

Short term phage-bacterial dynamics and a tragedy of the commons between two phage types. Free bacterial densities are in gray, refuge bacterial densities in black, genetically modified (GM) phage densities in red, and wild phage densities in blue. The rate at which refuge bacteria are released into the free state is in green, affected by enzyme density (not shown). Panels (A) and (B) represent cultures infected with single phage types. (A): The wild phage type has little effect on bacterial densities because it does not cause release of refuge bacteria; it maintains high levels by feeding on free bacteria released from the refuge. (B): The GM phage produces an enzyme that releases refuge bacteria. At high phage densities, refuge bacteria are released and killed rapidly, bacterial densities drop, and phage densities follow. (C): A tragedy of the commons. Both phages are present, and in the short term, the overall phage and bacterial dynamics follow a similar pattern as when only the GM phage is present, with refuge bacteria depleted (as in B). The wild phage has a slightly higher burst than the GM phage (20 versus 17); although both phages start out equally abundant, the GM phage declines and is eventually lost if the run is continued further, the dynamics returning to the pattern in (A). Loss of the GM phage is the ‘tragedy,’ since the GM phage releases refuge bacteria. (D): As in (C), but the wild phage is given the lower burst size (17 versus 20) and it is progressively lost. There is no tragedy because GM phage is maintained. When the GM phage is lost (in C), there is an earlier recovery of bacterial densities and earlier return of the release rate to baseline than in (D). The scale of the vertical axis is log ₁₀.