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

ABSTRACT

Evolutionary selection pressures that resulted in microbes found within environmental reservoirs that can cause diseases in animals are unknown. One hypothesis is that 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. All these strains 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.

One hypothesis why some microbes cause disease in humans is that they have been exposed to selection pressures in the environment, like predation by amoebae. This study selected yeast strains resistant to amoeba. One is due to the loss of calcineurin, a protein required for disease.