Calcium limitation induces expression of the type III secretion system in <i>P. aeruginosa</i> PAO1.

<p>(A) <i>P. aeruginosa</i> PAO1 <i>exoS-lux</i> was used as a reporter for activation of the T3SS in BM2 media supplemented with varying amounts of magnesium and calcium. Gene expression was measured every 20 minutes for 18 hours and the maximal gene expression is shown. The values shown are the means from triplicate experiments and the error bars represent the standard deviation. All values differ significantly (p<0.02 by unpaired <i>t</i>-test) from the control (2 mM Mg²⁺, 2 mM Ca²⁺). (B) Growth curves in BM2 media with corresponding magnesium and calcium concentrations. (C) Raw CPS illustrating the kinetics of <i>exoS-lux</i> expression in various magnesium and calcium concentrations. Similar curves have been observed for <i>exoT-lux</i> and <i>exoY-lux</i> expression over time (data not shown). Each experiment was performed at least three times and representative curves are shown.