Interaction of fungi with predatory amoeba - an environmental training ground for pathogens?
Members of the fungal kingdom belong to the most versatile eukaryotes and have conquered nearly all corners of the planet playing central roles in the carbon and nitrogen cycle. Moreover, some of them are important player in biotechnology or have become model organisms for genetics and cell biology. Of all, only a vanishingly small minority of species are of current concern for ecology and even human health. Nevertheless, Aspergillus, Candida or Cryptococcus account for approximately 2 million life-threatening infections per year with extremely high mortality rates ranging from 25-90%. A yet-unsolved question is how these three fungi which are normally live as saprophytes or harmless commensals have become such successful pathogens, able to withstand innate immune cells of humans and higher animals.
We hypothesize that the answer lies at least in part in the ecology of these fungi. In their natural habitats fungi are constantly exposed to microbial predators throughout their evolutionary history and since well before the emergence of innate immunity. We could show that phagocytic interactions between the soil amoeba, Dictyostelium discoideum and A. fumigatus showed striking similarities to encounters with macrophages. To further expand our model and to demonstrate that such predatory interactions actually occur in natural habitats, we have recently isolated and identified Protostelium aurantium, an amoeba which feeds exclusively on fungi including most Candida species, but also kills filamentous fungi such as A. fumigatus. I will present our first insights to the highly efficient killing mechanisms of this amoeba and how these could have imposed selection pressure to develop virulence determinants.
Hosts: Justyna Wolinska & Michael Monaghan