Calcium Chelation by Alginate Activates the Type III Secretion System in Mucoid Pseudomonas aeruginosa Biofilms
Figure 2
Exogenous alginate and DNA induce expression of the T3SS in P. aeruginosa planktonic cultures.
P. aeruginosa PAO1 exoS-lux, exoT-lux and exoY-lux were used as reporter strains to monitor expression of the T3SS. (A) Bioluminescence gene expression assays were used to measure exoS-lux expression in planktonic cultures of PAO1 grown in BM2 with 0.2 mM Ca2+ and 0.5 mM Mg2+ and supplemented with various concentrations of NTA, exogenous DNA or alginate. (B) Gene expression assays were used to measure exoT-lux and exoY-lux expression in planktonic cultures of PAO1 grown in BM2 with 0.2 mM Ca2+ and 0.5 mM Mg2+ and supplemented with various concentrations of alginate (C) or (D) extracellular DNA. 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. Values that differ significantly (p<0.02 by unpaired t-test) from the controls (BM2 alone) are marked with an asterisk. Each experiment was performed at least three times and representative values are shown.