The upregulation of pyoverdin by phosphate limitation was surprising given that the expression of pyoverdin genes is regulated by the transcriptional regulator PvdS that by itself is part of the FUR regulon, and as such the expression of PvdS and its regulated genes strongly depends on iron concentration. One would assume that there is going to be more iron available at lower concentrations of phosphate since phosphate causes precipitation of iron, thereby decreasing its effective concentration. Indeed, the absence of STI571 activation of FUR-regulated genes (normally suppressed at high selleck kinase inhibitor concentration of iron) suggested that iron was available for P. aeruginosa (Figure 4A) indicating that the
response of P. aeruginosa at differing levels of Pi is not simply a matter of the interaction of iron and phosphate, but rather involves more complex yet- to- be elucidated mechanisms. Alternatively,
the expression of pyoverdin genes and FUR regulon in high phosphate media at pH 7.5 (Figure 4B) demonstrated that P. aeruginosa was exposed to iron limiting conditions. Comparison of the signature of iron related genes during pH shift to 7.5 to that induced by iron limitation as reported by Ochsner et. al.  (Figure 4C) confirmed that P. aeruginosa experiences iron limitation at pH 7.5. Importantly, providing phosphate at pH 6.0 suppressed the expression of iron-related genes indicating a significant protective effect of phosphate supplementation www.selleckchem.com/products/gs-9973.html at pH6.0. Figure 4 The effect of phosphate and pH on the expression of pyoverdin-related genes. (A, A’) Transcriptional pattern response of P. aeruginosa PAO1 to phosphate limitation (< 0.1 mM) displayed at different scales: (A) in the absence of phosphate-related genes and (A') in the presence of phosphate-related genes. Pattern was drawn based on the results of Zaborin et al., 2009. (B) Transcriptional pattern response
of P. aeruginosa PAO1 to a pH shift from 6.0 to 7.5 during phosphate sufficiency (25 mM). Pattern was drawn based on the current Baricitinib data. (C) Transcriptional response of IS (mainly pyoverdin-related genes) and FUR regulon in P. aeruginosa PAO1 during iron limitation. Pattern was drawn based on the results of Ochsner et al., 2002. Light green dots represent the fold expression in pyoverdin-related genes; dark green dots – FUR-regulated genes. The dark green circle surrounding pvdS indicates that this gene is regulated by FUR. The brown spots indicate genes involved in pyocyanin biosynthesis, red spots indicate genes belonging to MvfR and MvfR-regulated pqsABCDE operon, and pink spots indicate genes of quorum sensing regulatory elements such as rhlI, rhlR, lasI, lasR, gacA, vfR, qscR. The dark circle surrounding qscR indicates that this gene is involved in the regulation of pyocyanin biosynthesis. Blue spots in the panel A’ represent phosphate-related genes.