Trends in Microbiology
ReviewGrowth of Legionella pneumophila in Dictyostelium discoideum: a novel system for genetic analysis of host–pathogen interactions
Section snippets
The L. pneumophila–D. discoideum model system
In our model system4, infection of Dictyostelium discoideum with L. pneumophila parallels the infection of mammalian macrophages and the fresh-water amoebae Hartmannella vermiformis and Acanthamoeba castellanii. A comparison of these systems is shown in Table 1. Infection of D. discoideum with L. pneumophila requires an incubation temperature of 25.5°C. This infection temperature is lower than that of macrophages and amoebae because D. discoideum does not survive in temperatures.27°C. This is a
Genetic analysis in D. discoideum
D. discoideum has many properties that make it amenable to genetic analysis. It is haploid with a small, 34-Mb genome and is easy to grow and maintain in the laboratory. Many genetic tools are already available for use with this organism because of pioneering work by developmental and cell biologists17. Genes can be ectopically expressed on plasmids and targeted for disruption by homologous recombination. It is possible to make knock-out mutations using restriction-enzyme-mediated integration
Analysis of known D. discoideum mutants
Another resource available for D. discoideum research is the large pool of defined mutants that can be tested for their effects on L. pneumophila growth. All of the mutants tested so far support near-wild-type levels of L. pneumophila intracellular growth, including cells that are slow growing and have severely altered morphology, such as the PI3-kinase double mutant19. This result is consistent with the finding that the PI3-kinase inhibitor Wortmannin does not block growth of L. pneumophila in
Conclusion
The L. pneumophila–D. discoideum system provides an exciting opportunity to use genetics to examine the host functions required for growth of an intracellular pathogen. Any intracellular pathogen that can grow at 25°C might be able to grow in D. discoideum, and in the future it could be possible to use D. discoideum genetics to examine the host requirements for growth of other pathogens.
Acknowledgements
We thank Susan VanRheenen and Guillame Duménil for careful reading of the manuscript and thank the many people in the D. discoideum field who cheerfully provided strains, technical advice and encouragement. J.M. Solomon receives support from an NRSA award from the NIH and R.R. Isberg is an investigator of the Howard Hughes Medical Institute.
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