Isolation of a fungal calcineurin A mutant suggests that amoebae can counter-select virulence attributes of microbes.

Evolutionary selection pressures that resulted in microbes found within environmental reservoirs that can also cause diseases in animals are unknown. One hypothesis is predatory organisms select microbes able to counteract animal immune cells. Here, a non-pathogenic yeast, Sporobolomyces primogenomicus, was exposed to predation by Acanthamoeba castellanii. Strains emerged that were resistant to being killed by this amoeba. These strains all had altered morphology, growing as pseudohyphae. The mutation in one strain was identified: CNA1 encodes the calcineurin A subunit that is highly conserved in fungi and where it is essential for their virulence in hosts including mammals, insects and plants.