Protozoan predation by amoebae is an oft-forgotten but highly potent evolutionary force in bacterial populations. It has been hypothesized that soil amoebae may select for increased pathogenicity in their bacterial prey. In order to understand the traits that result from continuous protozoan predation, we performed short and long term evolution experiments in which Pseudomonas fluoresecens SBW25 were continually preyed upon by a wild isolate of Acanthamoeba sp.. We observed rapid diversification in the bacterial colony morphologies in both experiments and determined that the earliest realized mutations tuned cellulose production by affecting the Wsp pathway in various ways. A longer, co-evolution experiment demonstrated that prey and predators co-adapt to one another in surprising ways. I will discuss our current understanding of the underlying molecular nature of these mutations and how these experiments shed light on host adaptation by bacterial pathogens.