We use model pathogenesis systems to identify virulence-related genes in bacterial and fungal pathogens, to identify host innate immunity genes in the nematode Caenornabditis elegans and the plant Arabidopsis thaliana, and to identify anti-microbial compounds in whole-animal high throughput screens.
Many human bacterial pathogens including Pseudomonas aeruginosa and Staphylococcus aureus are pathogens of C. elegans. P. aeruginosa is also a pathogen of Arabidopsis and Drosophila melanogaster. An advantage of using non-vertebrate model hosts is that thousands of bacterial or fungal clones from a mutagenized library can be individually screened for avirulent mutants in separate plants, in separate insects, or on separate petri plates seeded with C. elegans. From the perspective of the host, genetic analysis can be used to identify host genes involved in pathogen defense (innate immunity) by screening for pathogen-susceptible or pathogen-resistant mutants. Remarkably, many bacterial and fungal pathogenesis-related genes that are required for mammalian pathogenesis are also required for pathogenesis in model non-vertebrate hosts.
To facilitate the study of P. aeruginosa virulence, we constructed a so-called non-redundant P. aeruginosa transposon mutation library that contains approximately 5,800 individually sequenced insertions in more than 75% of P. aeruginosa genes. We are screening this library in different model hosts to identify as many virulence-related genes as possible as well as using genomic approaches to compare virulence of different P. aeruginosa strains.
From the host perspective, we have isolated Arabidopsis and C. elegans mutants that exhibit enhanced susceptibility or enhanced resistance to various pathogens. In C. elegans, we are studying the role of two highly conserved signaling cascades in innate immunity, the p38 MAPK and the DAF-2 insulin-like signaling pathways. In Arabidopsis, we are focusing on microarray and genetic analysis to identify components of signal transduction cascades activated by pathogen-associated molecular pattern molecules (PAMPs) such as bacterial flagellin.
Finally, because C. elegans is small enough to fit into a well in a 384-well microtiter plate and because various pathogens cause persistent lethal infections in the C. elegans intestine, we have been able to develop fully automated high throughput screens for compounds that “cure” C. elegans of either a bacterial or a fungal infection.
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