A Primer on Phage-Bacterium Antagonistic Coevolution

Abstract

The primary emphasis of this monograph has been on how one population, particularly of a given phage type, can drive the evolution of a second population, particularly of a given bacterium type. Less simplisitic, instead two populations can drive each other’s evolution and thereby co-evolve. When two populations are coevolving in a conflicting manner, we can describe this as antagonistic coevolution. It can be more straightforward, however, to envision two cooperating populations coevolving, e.g., an uninduced prophage and its host, and for them to coevolve with substantial exclusivity. With antagonistic coevolution, by contrast, there often can be little guarantee that the antagonistic interactions will be limited to between only two populations. Still, this chapter considers some basics regarding antagonistic coevolution as in principle this could occur between only one particular, especially strictly lytic phage, and one particular at least initially susceptible bacterium. The phage will tend to evolve toward having a greater negative impact on the bacterial population while the bacterium will tend to evolve toward interfering with that phage-mediated negative impact. More generally, bacterial variants will tend to be selected toward being less negatively affected by phages while phages will tend to be selected to overcome those bacterial tendencies. There can, however, be a number real-world complications on such processes and their interpretation, as this chapter considers.