FIG. 4.

Growth (a) and expression kinetics (b) of a reporter for a virulence gene per cell in DC3000-lux (P. syringae pv. tomato DC3000 hopA1::mini-Tn5 lux Cm^r). Cells were harvested from batch culture in hrp-inducing minimal medium with various concentrations of Fe³⁺. Note that Fe³⁺ levels above 300 μM are growth inhibitory (Fig. 5) but that the expression of the virulence gene is enhanced significantly after 10 h by addition of iron at levels greater than 300 μM. MALU, mega-ALU; X, cell mass measured by optical density; P, expression of a virulence gene as measured by luminescence.