A hidden battle in the dirt: soil amoebae interactions with Paracoccidioides spp

Abstract

Paracoccidioides spp. are thermodimorphic pathogenic fungi endemic to Latin America. Predation is believed to drive the evolution of virulence for soil saprophytes. We evaluated the presence of environmental amoeboid predators in soil from armadillo burrows where Paracoccidioides had been previously detected and tested if interaction of Paracoccidioides with amoebae increased fungal virulence. Nematodes, ciliates and amoebae - all potential predators of fungi - grew in cultures from soil samples. Microscopical observation and ITS sequencing identified the amoebae as Acanthamoeba spp, Allovahlkampfia spelaea and Vermamoeba vermiformis. These three amoebae efficiently ingested, killed and digested Paracoccidioides spp. yeast cells, as did laboratory-adapted axenic Acanthamoeba castellanii. Sequential co-cultivation of Paracoccidioides with A. castellanii selected for phenotypical traits related to survival of the fungus within a natural predator as well as in murine macrophages and in vivo (Galleria mellonella and mice). This increase in virulence is linked to the accumulation of cell wall alpha-glucans, polysaccharides that masks recognition of fungal molecular patterns by host pattern recognition receptors. Altogether, our results indicate that Paracoccidioides inhabits a complex environment with multiple amoeboid predators that can exert selective pressure to guide the evolution of virulence traits.