STX2 and infection: To test this idea and to determine the impact of population structure on its resistance to protist predation, we measured bacterial and Tetrahymena survival in cocultures containing Tetrahymena, EDL933 (phage+/Stx2+) or EDL933Δstx (phage+/Stx−) and varying ratios of bacteria that are either susceptible (MG1655) or immune (MG1655λimm933W) to infection by the stx2 phage in EDL933.