DECIPHERING THE ROLE OF CHEMICAL COMMUNICATION IN BACTERIAL COLONIZATION AND WARFARE BETWEEN PATHOGENS

There is a growing understanding that bacteria have an intriguing and dynamic three dimensional population organization. This organization plays a key role in their capacity to grow, divide, and respond to environmental changes. The bacteria in such an organization depend on communication in order to take advantage of it. The phenomenon of bacterial communication is termed quorum sensing. This is a process that allows bacteria to communicate using secreted chemical signaling molecules called autoinducers. This process enables a population of bacteria to collectively regulate gene expression and, therefore, behavior. In this study we examine the ability of two competing human pathogens to sense and respond to the secreted signaling molecules of each other.

Streptococcus pneumoniae is a Gram-positive bacterium. In S. pneumoniae, several quorum sensing systems have been identified. Pseudomonas aeruginosa is a Gram-negative rod. P. aeruginosa is a free-living bacterium, commonly found in soil and water. P. aeruginosa is an opportunistic pathogen that uses quorum sensing to coordinate the formation of biofilms, swarming motility, exopolysaccharide production, virulence, and cell aggregation.

Both bacteria, S. pneumoniae and P. aeruginosa, can be found in the respiratory tract, although rarely together. Therefore, our hypothesis is that there is chemical interplay between them and our goal is to identify intercellular signals that prevent encroachment of one pathogen toward another and to understand their mechanism of action. We have performed luminescence assays with reporter strains in order to observe inhibition or activation effects of the QS systems between bacteria. This was performed in order to test our hypothesis that S. pneumoniae secretes signaling molecules that have an effect on the QS system of P. aeruginosa.