T6SS-4 thermoregulation is OmpR-independent.

β-galactosidase activities (upper panel, in Miller units) and fluorescence levels (lower panel, in arbitrary units) of the T6SS-4 promoter fusions at 28°C and 37°C in the wild-type (A) and ompR1 transposon (B) strains. Identical results were obtained for the ompR2 transposon strain (data not shown). p-values obtained using paired Student’s t-test analyses are indicated (***, p≤0.0001).