Various bacterial pathogens and symbionts infect the amoeba Dictyostelium discoideum

The haploid soil amoeba Dictyostelium discoideum is a suitable model organism to study host-pathogen interactions with Legionella pneumophila. In this study we show that D. discoideum AX2 is also susceptible to infection with other important human pathogens and obligate intracellular symbionts. Infection assays demonstrated that Legionella-like amoebal pathogens (LLAP K62), Mycobacterium avium and the obligate intracellular endosymbionts of Acanthamoeba sp. strains TUME1, UWE25 and UWC6 were able to multiply within Dictyostelium. Salmonella typhimurium and Pseudomonas aeruginosa also invaded Dictyostelium, however were degraded shortly after uptake. Comitin-minus host cells were more permissive to infections with L. pneumophila and LLAP K62. Furthermore, this mutation significantly delayed the degradation of S. typhimurium. Accompanying electron and fluorescence microscopy of infected AX2 cells revealed that L. pneumophila and M. avium replicate within vacuoles, while LLAP K62, TUME1 and UWE25 were tightly enclosed by membranous structures within the cytoplasm. The beta-proteobacterium UWC6 was found to persist in the cytoplasm. The observed subcellular locations which correspond to the locations within the respective natural hosts suggest that D. discoideum is a representative model system for these pathogens and symbionts.