The genetics and phenotypes of Pseudomonas aeruginosa biofilm dispersal populations
Cystic fibrosis (CF) is a hereditary disease that is common among Caucasian populations. The leading cause of morbidity and mortality in CF patients is due to the persistent colonization of Pseudomonas aeruginosa in the lungs, resulting in chronic pulmonary exacerbations. The ability to colonize CF patients’ lungs and other environmental habitats has been attributed to the large genome size of P. aeruginosa, and its ability to form biofilms. The typical biofilm life cycle culminates in dispersal, where cells are released from the biofilm to colonize new sites and it is often associated with the emergence of phenotypic variants. It was found that a CF isolate, P. aeruginosa strain 18A, was able to generate four types of morphotypic variants during dispersal. In this study, phenotypes such as metabolic capacity, virulence factor expression and quorum sensing signal production were found to be significantly different between the dispersal variants and the parent. Similarly, an environmental P. aeruginosa isolate RS2 was found to generate three types of morphotypic variants during the dispersal phase of biofilm development. The dispersal variants of RS2 were also highly diverse in the phenotypes tested. In contrast, only a single morphotypic variant was observed for the laboratory strain PAO1. The dispersal variants of PAO1 differed from the parent in terms of metabolic capacity, but not in the expression virulence factors and quorum sensing signal production, suggesting that laboratory adaptation may have attenuated the ability of PAO1 to diversify during biofilm dispersal. 18A was found to grow more slowly and log phase cells were less viable compared to PAO1. The emergence of phenotypic variants for both 18A and PAO1 may not be due to an increase in mutation frequency of the biofilm population, suggesting that other mechanisms may be involved in variant formation. The genome of 18A was sequenced and its genotype was found to be different to PAO1 but highly similar to other sequenced P. aeruginosa strains, including an epidemic CF strain LESB58, and the highly virulent PA14, due to the presence of multiple genomic islands shared between the strains. It was found that several genes were deleted in 18A and that could explain the phenotypic differences, such as poor biofilm formation compared to PAO1. These studies could provide insight to better understand the virulence traits of P. aeruginosa and result in better prognosis for cystic fibrosis patients.
Variation, Cystic Fibrosis, Pseudomonas aeruginosa, Biofilm dispersal
Networked Digital Library of Theses and Dissertations