Quorum sensing and biofilm development in Pseudomonas aeruginosa

Bacteria communicate with each other via chemical signals to coordinate expression of specific genes in a cell density dependent fashion; a phenomenon called quorum sensing and response. Although we know that quorum sensing via acyl-homoserine lactone signals controls the expression of several virulence genes in the opportunistic human pathogen Pseudomonas aeruginosa, the number and types of genes controlled by quorum sensing have not been studied systematically. Using reporter gene technology, I identified 39 quorum sensing controlled (qsc) genes. The genes were organized into four general classes and represent possible targets for anti-Pseudomonas research.; To begin to understand the regulation of the four classes of qsc genes, I studied the importance of the stationary phase sigma factor rpoS on quorum sensing. These studies determined that there is a relationship between RpoS and quorum sensing where RpoS controls expression of the quorum sensing gene rhlI.; Because structural information of qsc gene promoters in P. aeruginosa is minimal, I determined the structure and minimal DNA elements required for expression of 3 qsc genes. My findings indicate that quorum-sensing-controlled promoters in P. aeruginosa are either specific for LasR or respond to both LasR and RhlR, and that critical bases in the promoter elements determine specificity.; Bacteria often exist as sessile biofilm communities. Biofilm bacteria are resistant to antimicrobial treatments and P. aeruginosa requires quorum sensing for proper biofilm development. I used DNA microarrays to study the differences between free-swimming and biofilm-grown P. aeruginosa cells and the mechanisms underlying biofilm resistance to antibiotics. Most P. aeruginosa genes were not differentially expressed in biofilm populations as compared to non-biofilm populations. About 0.5% of genes were activated and about 0.5% were repressed in biofilms. Some of the activated genes are known to affect antibiotic sensitivity of non-biofilm-grown P. aeruginosa. Exposure of biofilms to the antibiotic tobramycin caused differential expression of 20 genes. I conclude that gene expression in biofilm cells is similar to that in non-biofilm cells but there are a small number of significant differences.