Many bacteria grow on a surface in communities called biofilms. Cells growing in a biofilm are encapsulated by extracellular polymeric substances such as polysaccharides and proteins. Bacterial biofilms are medically important as a number of chronic infections, such as cystic fibrosis (CF) airway infections, endocarditis, and periodontitis, are strongly associated with biofilm formation. Biofilms cause pathological changes to infected tissues and are problematic due to their increased resistance to antibiotics and host clearance. Scientists and clinicians are investigating potential therapies directed at disrupting biofilm communities. It is therefore critical to elucidate the regulatory mechanisms controlling biofilm growth and development. Pseudomonas aeruginosa, a prominent CF pathogen, is one of the model organisms to study biofilm regulation.In this research proposal, we will study a novel system by which the P. aeruginosa biofilm extracellular polysaccharide PSL plays a role in serving as an extracellular signal, promoting production of the secondary messenger molecule c-di-GMP. We propose to focus on two aspects of this system:Specific Aim 1: Investigate the specific properties of PSL that determine its signalling activity.Specific Aim 2: Determine the c-di-GMP signal transduction pathway activated by PSL.Specific Aim 3: Determine the prevalence of the matrix intercellular signalling in other biofilm-forming organisms.