In nature bacteria predominantly live on surfaces, in matrix-encased communities called biofilms. Biofilm formation displays dynamic developmental patterns resembling those of multicellular organisms. Using cooperative traits such as cell-cell signaling, bacteria in biofilms form complex architectures, known as microcolonies, in which cells become highly differentiated from their planktonic counterparts. Microcolonies are generally highly tolerant to bactericides, rendering biofilms extremely difficult to eradicate. The aim of this study was to investigate the last, and least understood stage of biofilm development, which involves the coordinated dispersal of single cells that revert to a free-swimming planktonic phenotype and escape from the biofilm. Strategies to induce biofilm dispersal are of interest due to their potential to prevent biofilms and biofilm-related infections. In the model organism Pseudomonas aeruginosa, reproducible patterns of cell death and dispersal can occur within biofilm structures, leaving behind empty or hollow microcolonies. These events were previously linked with the appearance of oxidative and/or nitrosative stress in mature microcolonies. Here, the involvement of reactive oxygen and nitrogen intermediates in biofilm development and dispersal processes was investigated in both mono- and mixed-species biofilms. By using specific fluorescent dyes and P. aeruginosa mutant strains, nitric oxide (NO), a by-product of anaerobic respiration and an important messenger molecule in biological systems, was found to play a major role in P. aeruginosa biofilm dispersal. Further, the results demonstrated that exposure to physiological, non-toxic concentrations of NO (in the low nanomolar range) causes biofilm dispersal in P. aeruginosa and restores its vulnerability to conventional antimicrobials. By using microarray techniques, NO was shown to induce global changes in genetic expression, including enhanced metabolic activity and motility and decreased adhesion and virulence in P. aeruginosa biofilms. The regulatory pathway implicated c-di-GMP, a newly discovered messenger molecule involved in the transition from sessility to motility in many bacterial species. NO-mediated dispersal was also observed in other single- and multi-species biofilms of clinically and industrially relevant organisms. Hence, the combined exposure to NO and bactericides was identified as a potential novel strategy for the removal of microbial communities, providing a low cost and environmentally safe solution to biofilm control.
| Identifer | oai:union.ndltd.org:ADTP/187315 |
| Date | January 2007 |
| Creators | Barraud, Nicolas, School of Biotechnology And Biomolecular Sciences, UNSW |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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