Results demonstrated that the expression of pyoverdin can be prevented without providing iron by maintaining local phosphate abundance at pH 6.0. Figure 3 Pyoverdin production is significantly increased at basic pH and plays a major role in the virulence of P. aeruginosa. (A) Production of pyoverdin normalized to cell density in P. aeruginosa PAO1 grown in liquid NGM at varying pH. n = 3, *p < 0.05 between Pi25 mM, pH 7.5 and Pi25 mM, pH7.5 +Fe3+, 100 μM. (B) Effect of pH changes on pyoverdin production and growth (inserted panel) in P. aeruginosa PAO1 at

high Pi concentration (25 mM). (C) QRT-PCR demonstrating enhanced expression of iron-related but not phosphate- and QS-related genes. (D) PAO1 mutant deficient in the production of pyoverdin and pyochelin (ΔPvdD/ΔPchEF) is significantly attenuated in lethality in mice at pH 7.5. Mice were subjected EPZ015938 price to hepatectomy and intestinal injection with either wtPAO1 or its derivative mutant ΔPvdD/ΔPchEF. All mice were given 25 mM potassium phosphate buffered to pH 7.5 in their drinking water. Results were performed in duplicate. Cumulative survival is represented as Kaplan-Meyer survival curves, n = 10/group, p < 0.05, Log-Rank (Mantel-Cox). The effect

of pH on pyoverdin production measured by fluorescence as previously described [9] was verified in the range of 4.0 to 8.5 (Figure 3B). Results demonstrated that the pyoverdin production is similar between pH4.0 and 6.0 (low level of pyoverdin), and between pH7.5 and 8.5 (high level of pyoverdin). We noticed however that the growth of P. aeruginosa at pH 4.0 was greatly Nutlin-3a datasheet delayed up to 4 hrs (Figure 3B, inserted panel). At this point, the pH of bacterial culture changed on its own from 4.0 to 5.5 and further changed to pH ~ 6.0 at 9 hrs. Bacteria significantly increased their growth rate at 9 hours. Alternatively, bacteria grew very well at pH 8.5, produced pyoverdin, Ergoloid and there was no change from the initial pH. This finding supports our hypothesis that P. aeruginosa can regulate its environmental pH to facilitate its colonization. Next, we measured the

expression of QS- and iron- related genes by qRT-PCR in P. aeruginosa PAO1 grown for 9 hrs in liquid NGM media at pH 7.5 versus 6.0. Gene expression was normalized to tpiA (PA4748) expression and then fold change was determined using expression of PAO1 measured in NGM at pH 6.0 as 100%. Results demonstrated increased expression of iron related genes and decreased expression of both quorum sensing and low phosphate- related genes at pH 7.5 versus 6.0 (Figure 3C). These data may confirm that pH-mediated expression of iron- Wortmannin ic50 regulated genes is not dependent on quorum sensing. However, we found significant down-regulation (10 fold) of the qscR gene encoding LuxR-type “”orphan”" receptor QscR, a potent QS repressor [20].