Fight not flight: Parasites drive the bacterial evolution of resistance, not escape

In the face of ubiquitous threats from parasites, hosts can evolve strategies to resist infection or to altogether avoid parasitism, for instance by avoiding behavior that could expose them to parasites or by dispersing away from local parasite threats. At the microbial scale, bacteria frequently encounter viral parasites, bacteriophages. While bacteria are known to utilize a number of strategies to resist infection by phages, and can have the capacity to avoid moving towards phage-infected cells, it is unknown whether bacteria can evolve dispersal to escape from phages. In order to answer this question, we combined experimental evolution and mathematical modeling. Experimental evolution of the bacterium Pseudomonas fluorescens in environments with differing spatial distributions of the phage Phi2 revealed that the host bacteria evolved resistance depending on parasite distribution, but did not evolve dispersal to escape parasite infection. Simulations using parameterized mathematical m..., Bacteria & Phage Strains and Culturing
We used the widely-studied model system of P. fluorescens SBW25 and its strictly-lytic phage Phi2 (Brockhurst et al. 2007), which putatively binds the bacterial lipopolysaccharide (LPS) (Scanlan and Buckling 2012). We used variations of King’s B (KB) medium (the standard SBW25 bacterial media, see experimental evolution section below): 10 g/L LP0037 Oxoid Bacteriological Peptone, 15 g/L glycerol, 1.5 g/L potassium phosphate, and 0.6 g/L magnesium sulfate. Amplified phage stocks were created by infecting an actively growing SBW25 liquid culture, incubating while shaking for 24 hours at 28°C, then adding 25 µL chloroform per mL culture and storing at 4°C.
Measuring Phage & Bacterial Density
Phage and bacterial concentrations were quantified using standard plating and optical density measurements. Phages were quantified in plaque-forming-units per mL (PFU/mL) using a plaque assay: phage suspensions and 100 µL of an overnight bacterial culture..., , # Fight not flight: Parasites drive the bacterial evolution of resistance, not escape

[https://doi.org/10.5061/dryad.msbcc2g5c](https://doi.org/10.5061/dryad.msbcc2g5c)

## Abstract

In the face of ubiquitous threats from parasites, hosts can evolve strategies to resist infection or to altogether avoid parasitism, for instance by avoiding behavior that could expose them to parasites or by dispersing away from local parasite threats. At the microbial scale, bacteria frequently encounter viral parasites, bacteriophages. While bacteria are known to utilize a number of strategies to resist infection by phages, and can have the capacity to avoid moving towards phage-infected cells, it is unknown whether bacteria can evolve dispersal to escape from phages. In order to answer this question, we combined experimental evolution and mathematical modeling. Experimental evolution of the bacterium *Pseudomonas fluorescens* in environments with differing spatial distributions of the phage Phi2 reveal...