Transposon mobilization in the human fungal pathogen <i>Cryptococcus</i> is mutagenic during infection and promotes drug resistance in vitro.

Abstract

When transitioning from the environment, pathogenic microorganisms must adapt rapidly to survive in hostile host conditions. This is especially true for environmental fungi that cause opportunistic infections in immunocompromised patients since these microbes are not well adapted human pathogens. <i>Cryptococcus</i> species are yeastlike fungi that cause lethal infections, especially in HIV-infected patients. Using <i>Cryptococcus deneoformans</i> in a murine model of infection, we examined contributors to drug resistance and demonstrated that transposon mutagenesis drives the development of 5-fluoroorotic acid (5FOA) resistance. Inactivation of target genes <i>URA3</i> or <i>URA5</i> primarily reflected the insertion of two transposable elements (TEs): the T1 DNA transposon and the TCN12 retrotransposon. Consistent with in vivo results, increased rates of mutagenesis and resistance to 5FOA and the antifungal drugs rapamycin/FK506 (rap/FK506) and 5-fluorocytosine (5FC) were found when <i>Cryptococcus</i> was incubated at 37° compared to 30° in vitro, a condition that mimics the temperature shift that occurs during the environment-to-host transition. Inactivation of the RNA interference (RNAi) pathway, which suppresses TE movement in many organisms, was not sufficient to elevate TE movement at 30° to the level observed at 37°. We propose that temperature-dependent TE mobilization in <i>Cryptococcus</i> is an important mechanism that enhances microbial adaptation and promotes pathogenesis and drug resistance in the human host.