Fig. 5.

Serum does not interfere with the repression of pvdS expression by iron. PAO1/pPMP220 : : PpvdS was grown in the relevant media, and samples were obtained at the indicated time points and the level of β-galactosidase activity was determined. Values represent the means±sem of three independent experiments. ***, P<0.001; **, P<0.01; *, P<0.05. (a) Serum enhances pvdS expression when the intracellular pool of iron is depleted. The intracellular pool of iron was depleted by subculturing cells twice in TSB-DC and then adding ABS or continuing the cultures in TSB-DC alone. (b) Iron exogenously added to TSB-DC (high level, 20 µg ml⁻¹) represses pvdS expression. (c) High levels of exogenous iron override serum enhancement in pvdS expression. (d) Serum enhances pvdS expression in PAO1 grown in LB broth, a medium that contains low levels of iron.