Extracellular Polysaccharides in Pseudomonas aeruginosa
Colvin, Kelly Marie
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Biofilms are a prominent mode of bacterial growth in the environment and in disease. Biofilm development involves specific stages including surface adherence, proliferation, cell-cell cohesion and dispersion. Each of these stages is dependent on either the reinforcement or modulation of the extracellular matrix. A key component of the biofilm matrix is extracellular polysaccharides. Many organisms that are adept biofilm producers including <italic>Escherichia coli<italic>, <italic>Vibrio<italic> spp, <italic>Salmonella<italic> spp,<italic> Burkholderia<italic> spp. and <italic>Pseudomonas aeruginosa <italic>maintain the genetic material necessary to synthesize multiple types of polysaccharides. In many cases, the different polysaccharides are niche-specific and allow the organism to thrive in a variety of environments. <italic>P. aeruginosa<italic> is a model organism for biofilm studies and produces three extracellular polysaccharides that have been implicated in biofilm development, alginate, Psl and Pel. Significant work has been conducted on the roles of alginate and Psl in biofilm development, however we know little regarding Pel. In this study, I demonstrated that Pel can serve two functions in biofilms. The first is that Pel provides cell-cell adhesion during biofilm growth and can act as the primary structural scaffold. The second is that Pel enhances tolerance to aminoglycoside antibiotics in biofilm populations, a property unique to Pel. Additionally, this work has laid the foundation for Pel purification and carbohydrate structural analysis and contributed to the biochemical analysis of two proteins involved in Pel synthesis, PelD and PelF. Furthermore, I demonstrated that Pel and Psl polysaccharides provide structural redundancy in the biofilm matrix and the structural contribution of each polysaccharide was highly variable between clinical and environmental isolates. This led us to propose four classes of strains based upon their Pel and Psl functional and expression profiles. From this work, we have gained important insight on the unique and redundant roles of two distinct polysaccharides that are important factors in the adaptation of <italic>P. aeruginosa <italic>for successful chronic infections in cystic fibrosis patients and biofilm growth.
- Microbiology