Involvement of the Quorum Sensing Circuitry in Surface-related Behaviors in Pseudomonas aeruginosa

Abstract

Bacteria must sense and respond to several environmental cues. Quorum sensing (QS) is an intercellular communication system that allows the synchronization of gene expression in a population-wide scale in response to variations in cell density. Importantly, responses to other environmental stimuli mediated by QS is dependent on its entanglement with the c-di-GMP signaling system. c-di-GMP is a second messenger involved in lifestyle transitions and, thus is key in bacterial adaptation. The presence of these regulatory systems partially explains the widespread colonization of Pseudomonas aeruginosa. This opportunistic pathogen is particularly important in the hospital environment and is frequently responsible for nosocomial infections. We have previously observed the upregulation of the oligopeptidase A (PrlC) in a high c-di-GMP background in P. aeruginosa PA14. prlC is in operon with a gene that codes for PA14_00800, a small hypothetical protein with a single domain of unknown function. To unravel the role of these proteins in P. aeruginosa physiology, the phenotypical characterization of their deletion strains was performed. Interestingly, in the absence of PA14_00800 several social behaviors are altered. For instance, the ability of DPA14_00800 to initiate biofilm is diminished as well as the production and/or secretion of Pel exopolysaccharide. The coordinated social translocation, referred as swarming motility, is also affected on DPA14_00800 in different aspects. Firstly, swarming colonies of this strain are smaller than the parental swarming colonies. Secondly, the classical behavior of swarming cells in which migrating cells tend to avoid high cellular-density microenvironments is altered. Here PA14 swarming colonies have the odd tendency to merge with DPA14_00800 swarming cells. In addition, the synthesis of pyoverdine, the major siderophore of P. aeruginosa is also negatively affected. Importantly, the severe reduction on pyoverdine production is only observed in solid or semisolid media. The social behaviors regulated by PA14_00800 thus have in common a surface-dependent component, indicating a role for PA14_00800 in surface-dependent mechanisms. Preliminary results indicate a role of PrlC in these phenotypes, as seen by the concomitant deletion of PA14_00800 and PrlC. This project aims to investigate the quorum sensing circuitry of DPA14_00800 and DprlC to unravel their significance in surface-related behaviors. The quantification of autoinducers, chemical molecules that mediate QS, will be performed by mass spectrometry both in liquid and solid medium. We also aim to purify and quantify rhamnolipids and their precursor, as they are key to swarming motility and regulate the dispersal pattern of swarming cells. The understanding of the mechanism by which PA14_00800 regulates surface-related behaviors is extremely important, mostly because it bears a conserved domain of unknown function and there is no information about it in the literature. The comprehension of the protein dynamics involved in this process is also important, as it can auxiliary the rational design of new drugs against P. aeruginosa.