Bacterial strains were grown in LB broth and supplemented with 50 μg·mL−1 rifampicin where indicated. A V. cholerae V52 (O37 serogroup) derivative strain lacking hlyA, rtxA, and hapA was the background strain for all T6SS deletion mutants and was used as the wildtype strain in all experiments (3). The V52ΔACD mutant was provided by John Mekalanos (Harvard Medical School, Cambridge, MA) (16). E. coli K-12 strain MG1655 (genotype F−, λ−, rph-1) was provided by Tracy Raivio (University of Alberta). mCherry was designed as described in ref. 24. Plasmid pTV-mCherry was a gift from Lieke B. van Alphen (University of Alberta). Spontaneous rifampicin-resistant strains were isolated by growth on 50 μg·mL−1 rifampicin.