Figure 2 ColR-regulated genes respond to excess of zinc. β-galactosidase activities measured in P. putida wild-type (wt), colR- and colS-deficient strains (colR and colS, respectively) carrying the transcriptional fusions of PP0268, PP0737, PP0035, PP0900, PP0903, PP1636, PP2579 or PP5152 promoters with lacZ in the plasmid p9TTBlacZ. P. putida wild-type was grown in LB medium or LB where 0.6 mM or 1.7 mM ZnSO4 was added. colR- and colS-deficient strains were grown in LB or LB supplemented with 0.6 mM

ZnSO4. Data (means with 95% confidence intervals) of at least three independent experiments are presented. Asterisks indicate statistically significant Selleck KPT 330 differences (p < 0.05, two-way ANOVA with post-hoc Tukey’s Unequal N HSD test) between values obtained in LB and in LB supplemented with ZnSO4. The excess of iron, manganese and cadmium can also affect the expression of the ColR regulon Data presented above show that besides being important in zinc resistance, the ColRS system is also required

for iron, manganese and cadmium resistance. To analyze whether other transition metals besides zinc can activate ColRS signaling, one ColR-activated (PP0903) and one ColR-repressed (PP0268) promoter was tested for metal responsiveness. The highest concentration of each metal tolerable to the colS mutant without growth retardation was used in this assay. Both ColR-regulated promoters respond to the excess of iron, manganese and cadmium, although the degree of response differs between different metals (Figure 3). To control IWR1 whether iron-, manganese- and cadmium-promoted regulation of PP0903 and PP0268 indeed depends on ColRS activation, the promoters were also tested in the colS-deficient background. As the absence

of ColS abolished the response of the promoters to metals (Figure 3), we conclude that four transition metals – zinc, iron, mTOR inhibitor manganese and cadmium – can activate the ColRS signal transduction pathway. In accordance with MIC measurements, Co2+, Cu2+ and Ni2+ did not influence transcription from the ColR regulon genes, indicating that these metals do not produce the signal for the ColRS system. Figure 3 ColR-regulated genes respond to excess of zinc, iron, manganese and cadmium. β-galactosidase activities measured in P. putida wild-type (wt) and colS-deficient strain (colS) carrying the transcriptional fusions of PP0268 or PP0903 promoters with lacZ in the plasmid p9TTBlacZ. Bacteria were grown in LB medium and in LB containing either 0.6 mM ZnSO4, 0.15 mM FeSO4, 0.5 mM MnCl2, 0.1 mM CoCl2, 2 mM CuSO4, 0.5 mM NiSO4 or 0.2 mM CdSO4. Data (means with 95% confidence intervals) of at least three independent experiments are presented. Asterisks indicate statistically significant differences (p < 0.05, two-way ANOVA with post-hoc Tukey’s Unequal N HSD test) between values obtained in LB and in LB supplemented with metal salt.