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. 2007 Mar 15;117(4):877–888. doi: 10.1172/JCI30783

Figure 7. Repression of pyoverdine expression via the transcriptional regulator pvdS contributes to Ga’s antimicrobial activity.

Figure 7

(A) Overriding pvdS repression protects P. aeruginosa from the growth-inhibitory effects of Ga. P. aeruginosa containing the arabinose-inducible pvdS construct or an empty vector were grown in biofilm medium with or without 5 μM Ga and 0.05% arabinose (arabinose was present from the beginning of the experiment). Results are the mean of 3 experiments; error bars are SEM; *P < 0.001 versus untreated control; ‡P < 0.001 versus 5 μM Ga. Consistent with this result, inactivation of pvdS somewhat increased Ga sensitivity (see Supplemental Figure 11). (B) The protective effect of pvdS expression depends on pyoverdine. The pvdA mutant containing the inducible pvdS construct or the empty vector was grown in biofilm medium with or without 5 μM Ga, 0.05% arabinose, or 20 μM of pyoverdine. The protective effect of overriding pvdS repression during Ga treatment that was seen in WT cells (A) was lost in the pvdA mutant. (C) Pyoverdine protects P. aeruginosa from the growth-inhibitory effects of Ga. The pvdA mutant was grown in biofilm medium with or without 5 μM Ga, 20 μM Ga, and 20 μM of pyoverdine. Exogenous addition of pyoverdine protected bacteria from the growth-inhibitory effects of 5 μM Ga. Higher levels of Ga (20 μM) overcome the protective effects of pyoverdine. Results are the mean of 3 experiments; error bars are SEM; *P < 0.001 versus untreated control; ‡P < 0.001 versus 5 μM Ga; ΧP < 0.001 versus 5 μM Ga plus 20 μM pyoverdine.