Characterization and regulation of anti-eukaryote factors in Pseudomonas fluorescens. NZI7

• Main Author: Burlinson, Peter
• Published: University of Oxford 2008
• Subjects: 579.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491327

This study examined Pseudomonas 'NZ strains' that cause blotch disease on the commercial mushroom Agaricus bisporus. Mushroom-pathogenic Pseudomonas represent an interesting example of bacteria associated with a fungal host system. The mycosphere also contains other organisms that Pseudomonas may interact with, thus strains isolated from this environment may also contribute towards our understanding of the molecular basis of opportunistic pathogenesis and bacterial survival in nature. Phylogenetics was used to assess the relatedness of NZ strains and their position in the Pseudomonas genus. It was hypothesised that NZ strains may possess means to resist predators and parasitize other eukaryotes present in the mycosphere. Evidence for this was sought by assessing their interactions with several fungi, the nematode Caenorhabditis elegans and the social amoeba Dictyostelium discoideum. The differential interactions observed suggest some strains have specific mechanisms to antagonize bacteriovores. NZ strains were surveyed for production of potentially antagonistic exofactors and also for possession of type III secretion systems, which were identified in several strains. The phylogenetic distribution of these factors suggests traits such as cyanide production, exochitinase activity and type III secretion may be restricted to certain P.f1uorescens lineages. Transposon mutagenesis of strain NZI7 showed production of the toxin tolaasin was essential for production of brown blotch symptoms but appeared not to influence C.elegans or D.discoideum interactions. Cyanide production influenced both A.bisporus and C.elegans interactions. A novel screening procedure identified NZI7 mutants with decreased resistance to C.elegans feeding and identified a gene cluster hypothesized to produce a metabolite contributing to the NZI7 inedibility phenotype. The expression of these genes was characterised using luxCDABE transposon reporter mutants and the global sensor kinase GacS was found to control their expression. GacS was also found to regulate the production of anti-fungal factors in strain NZ011.