Journal
FRONTIERS IN MICROBIOLOGY
Volume 6, Issue -, Pages -Publisher
FRONTIERS MEDIA SA
DOI: 10.3389/fmicb.2015.00902
Keywords
cell aggregates; extracellular polysaccharide; gene regulation; iron uptake; mechanosensor; Pseudomonas aeruginosa; siderophore; virulence
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Funding
- Italian Cystic Fibrosis Research Foundation [10/2013]
- Sapienza University of Rome
- Italian Ministry of University and Research-PRIN [prot. 2012WJ5X8K]
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In Pseudomonas aeruginosa the Gac signaling system and the second messenger cyclic diguanylate (c-di-GMP) participate in the control of the switch between planktonic and biofilm lifestyles, by regulating the production of the two exopolysaccharides Pel and Psi. The Gac and c-di-GMP regulatory networks also coordinately promote the production of the pyoverdine siderophore, and the extracellular polysaccharides Pel and Psi have recently been found to mediate c-di-GMP-dependent regulation of pyoverdine genes. Here we demonstrate that Pel and Psi are also essential for Gac mediated activation of pyoverdine production. A pet psi double mutant produces very low levels of pyoverdine and shows a marked reduction in the expression of the pyoverdine-dependent virulence factors exotoxin A and PrpL protease. While the exopolysaccharide-proficient parent strain forms multicellular planktonic aggregates in liquid cultures, the Pel and Psi-deficient mutant mainly grows as dispersed cells. Notably, artificially induced cell aggregation is able to restore pyoverdine-dependent gene expression in the pet psi mutant, in a way that appears to be independent of iron diffusion or siderophore signaling, as well as of recently described contact-dependent mechanosensitive systems. This study demonstrates that cell aggregation represents an important cue triggering the expression of pyoverdine-related genes in P aeruginosa, suggesting a novel link between virulence gene expression, cell cell interaction and the multicellular community lifestyle.
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