Abstract
Quorum sensing (QS) in Pseudomonas aeruginosa coordinates the expression of virulence factors, such as exoproteases and siderophores, that are public goods utilized by the whole population of bacteria, regardless of whether they invested or not in their production. These public goods can be used by QS defective mutants for growth, and since these mutants do not contribute to public goods production, they are considered social cheaters. Pyocyanin is a phenazine that is a toxic, QS-controlled metabolite produced by P. aeruginosa. It is a redox-active compound and promotes the generation of reactive oxygen species; it also possesses antibacterial properties and increases fitness in competition with other bacterial species. Since QS-deficient individuals are less able to tolerate oxidative stress, we hypothesized that the pyocyanin produced by the wild-type population could promote selection of functional QS systems in this bacterium. Here, we demonstrate, using competition experiments and mathematical models, that, indeed, pyocyanin increases the fitness of the cooperative QS-proficient individuals and restricts the appearance of social cheaters. In addition, we also show that pyocyanin is able to select QS in other bacteria such as Acinetobacter baumannii.
Highlights
Pseudomonas aeruginosa uses Quorum sensing (QS) to estimate its population density and to reprogram its gene expression and behavior
The only way mutants can grow is by utilizing the peptides and amino acids produced by the hydrolysis of casein by the QScontrolled exoproteases synthetized and exported by the wildtype strain; lasR rhlR mutants behaved as social cheaters that exploit the cooperator individuals (Diggle et al, 2007; García-Contreras et al, 2015b)
We demonstrated that pyocyanin is able to select functional QS systems in both P. aeruginosa and A. baumannii
Summary
Pseudomonas aeruginosa uses QS to estimate its population density and to reprogram its gene expression and behavior . Since the production of public goods is costly, the individuals that use them without contributing to their production are social cheaters (Diggle et al, 2007) and can invade the population, causing a tragedy of the commons (Sandoz et al, 2007). It has been demonstrated in P. aeruginosa that cheating behavior exists for both exoprotease production (Diggle et al, 2007) and for the production of the main siderophore pyoverdine (Kummerli et al, 2009). Mutants unable to produce pyoverdine are selected in iron deficient media (Dumas and Kummerli, 2012)
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