Figure 3. The type VI secretion system is required for Francisella escape from the phagosome following cell-cell transfer.

(A) The percent of bacteria enclosed in a LAMP-1 positive vacuoles 3 hr after a synchronized infection with extracellular bacteria. These data represent the ability of the inducible type VI secretion system (T6SS) strain to escape the initial phagosome during a conventional infection under the inducible expression condition. (B) The percent of bacteria enclosed in LAMP-1 positive vacuoles after cell-cell transfer. Under conditions where the inducible strain is not producing the T6SS, the bacteria remain largely trapped while the wildtype strain continues to escape the phagosome over time. From three independent experiments with 50 infected cells counted per experiment per time point. Mean ± standard deviation. Panel A used a One-way Anova with Dunnett post-test. Panel B used a Student t-test to compare between time points. **p<0.01, ***p<0.001, ns – not significant.

Figure 3—figure supplement 1. The F. tularensis type VI secretion system is dispensable for intracellular growth following phagosomal escape.

Colony forming units of wildtype, the parent ΔdotU strain and the ΔdotU strain with dotU under an anhydrous tetracycline inducible promoter. Pre-induced indicates that the bacteria were only exposed to ATc in the overnight and not during or after inoculation of the BMDMs. This assay was performed three times in triplicate and the data represents the mean ± standard deviation. One-way ANOVA with Dunnett post-test. *p<0.05, **p<0.01, **p<0.001.