ABSTRACTBacteria inhabiting biofilms usually produce one or more polysaccharides that provide a hydrated scaffolding to stabilize and reinforce the structure of the biofilm, mediate cell-cell and cell-surface interactions, and provide protection from biocides and antimicrobial agents. Historically, alginate has been considered the major exopolysaccharide of thePseudomonas aeruginosabiofilm matrix, with minimal regard to the different functions polysaccharides execute. Recent chemical and genetic studies have demonstrated that alginate is not involved in the initiation of biofilm formation inP. aeruginosastrains PAO1 and PA14. We hypothesized that there is at least one other polysaccharide gene cluster involved in biofilm development. Two separate clusters of genes with homology to exopolysaccharide biosynthetic functions were identified from the annotated PAO1 genome. Reverse genetics was employed to generate mutations in genes from these clusters. We discovered that one group of genes, designatedpsl, are important for biofilm initiation. A PAO1 strain with a disruption of the first two genes of thepslcluster (PA2231 and PA2232) was severely compromised in biofilm initiation, as confirmed by static microtiter and continuous culture flow cell and tubing biofilm assays. This impaired biofilm phenotype could be complemented with the wild-typepslsequences and was not due to defects in motility or lipopolysaccharide biosynthesis. These results implicate an as yet unknown exopolysaccharide as being required for the formation of the biofilm matrix. Understandingpsl-encoded exopolysaccharide expression and protection in biofilms will provide insight into the pathogenesis ofP. aeruginosain cystic fibrosis and other infections involving biofilms.

Jackson, K. D., Starkey, M., Kremer, S., Parsek, M. R., & Wozniak, D. J. (2004). Identification ofpsl, a Locus Encoding a Potential Exopolysaccharide That Is Essential forPseudomonas aeruginosaPAO1 Biofilm Formation. Journal of Bacteriology, 186(14), 4466–4475.