Proteomic analysis of the Pseudomonas aeruginosa iron starvation response reveals PrrF sRNA-dependent iron regulation of twitching motility, amino acid metabolism, and zinc homeostasis proteins.

Iron is a critical nutrient for most microbial pathogens, and the immune system exploits this requirement by sequestering iron. The opportunistic pathogen Pseudomonas aeruginosa exhibits a high requirement for iron yet an exquisite ability to overcome iron deprivation during infection. Upon iron starvation, P. aeruginosa induces the expression of several high affinity iron acquisition systems, as well as the PrrF sRNAs that mediate an iron-sparing response. Here, we used liquid chromatography-tandem mass spectrometry to conduct proteomics of P. aeruginosa's iron starvation response. Iron starvation increased levels of multiple proteins involved in amino acid catabolism, providing the capacity for iron-independent entry of carbons into the TCA cycle. Proteins involved in sulfur assimilation and cysteine biosynthesis were reduced upon iron starvation, while proteins involved in iron-sulfur cluster biogenesis were increased, highlighting the central role of iron in P. aeruginosa metabolism. Iron starvation also resulted in changes in the expression of several zinc-responsive proteins and increased levels of twitching motility proteins. Subsequent analyses provided evidence for regulation of many of these proteins via post-transcriptional regulatory events, some of which are dependent upon the PrrF sRNAs. Moreover, we showed that iron-regulated twitching motility is partially dependent upon the prrF locus, highlighting a novel link between the PrrF sRNAs and motility. These findings add to the known impacts of iron starvation in P. aeruginosa and outline potentially novel roles for the PrrF sRNAs in iron homeostasis and pathogenesis. IMPORTANCE Iron is central for growth and metabolism of almost all microbial pathogens, and as such this element is sequestered by the host innate immune system to restrict microbial growth. Here we used label-free proteomics to investigate the Pseudomonas aeruginosa iron starvation response, revealing a broad landscape of metabolic and metal homeostasis changes that have not previously been described. We further provide evidence that many of these processes, including twitching motility, are regulated through the iron-responsive PrrF small regulatory RNAs. As such, this study demonstrates the power of proteomics for defining stress responses of microbial pathogens.