Distinct roles of extracellular polymeric substances in Pseudomonas aeruginosa biofilm development

Bacteria form surface attached biofilm communities as one of the most important survival strategies in nature. Biofilms consist of water, bacterial cells and a wide range of self-generated extracellular polymeric substances (EPS). Biofilm formation is a dynamic self-assembly process and several distinguishable stages are observed during bacterial biofilm development. Biofilm formation is shown to be coordinated by EPS production, cell migration, subpopulation differentiation and interactions. However, the ways these different factors affect each other and contribute to community structural differentiation remain largely unknown. The distinct roles of different EPS have been addressed in the present report. Both Pel and Psl polysaccharides are required for type IV pilus-independent microcolony formation in the initial stages of biofilm formation by Pseudomonas aeruginosa PAO1. Both Pel and Psl polysaccharides are also essential for subpopulation interactions and macrocolony formation in the later stages of P. aeruginosa PAO1 biofilm formation. Pel and Psl polysaccharides have different impacts on Pseudomonas quinolone signal-mediated extracellular DNA release in P. aeruginosa PAO1 biofilms. Psl polysaccharide is more important than Pel polysaccharide in P. aeruginosa PAO1 biofilm formation and antibiotic resistance. Our study thus suggests that different EPS materials play distinct roles during bacterial biofilm formation.