Quorum sensing, the ability of a bacterial species to monitor its own population density and activate specific genes at appropriate densities, is a common trait, critical for adaptation to environmental changes. These are two quorum sensing systems in Pseudomonas aeruginosa that control an ill-defined battery of virulence genes. One of the systems also is required for development of P. aeruginosa biofilms.
The aims of the proposed research are to identify the genes controlled by each of the two systems and to determine whether control of individual genes is direct of indirect. We will also determine which of the target genes we identify are required for biofilm development. Two approaches will be taken to identify target genes. I.P. aeruginosa quorum sensing mutants will be employed to identify proteins expressed at higher levels with or without each of the signal molecules. II. Mutagenesis of a P. aeruginosa quorum sensing null mutant with promoter probe transposons will be used to identify genes that require for their expression, the presence or absence of either of the quorum sensing signals. To determine whether quorum sensing control of target genes is direct of indirect we will examine expression of lacZ fusions to target gene promoters in recombinant Escherichia coli. To determine which targets of quorum sensing are required for normal biofilm development we will test mutants identified as quorum sensing regulated for their ability to form typical P. aeruginosa structured, biocide resistant biofilms. It is clear that the role of quorum sensing in the general regulatory circuits of the cell is complex, yet this has not been investigated systematically. The proposed research will open a new area of study in bacterial cell-to-cell communication. P. aeruginosa is an appropriate model for these studies for several reasons. The genome is being sequenced (most of the genome sequence is already available for analysis). There are two well-characterized quorum sensing systems in P. aeurginosa and appropriate null mutations have been constructed. Although there have been no systematic surveys, we know that quorum sensing in P. aeruginosa controls expression of many unlinked genes. Quorum sensing has been shown to be critical for P. aeruginosa virulence in several animal or plant model systems.
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