Tools for genetic manipulation of the endemic fungal pathogen, Emergomyces africanus, and the application of a fluorescent reporter strain in infection models.

Emergomyces africanus is a thermally dimorphic fungal pathogen endemic to Southern Africa, which can cause fatal systemic infections in persons with advanced HIV disease. Its mechanisms of pathogenesis are not well understood. Characterisation of virulence traits in this pathogen requires appropriate molecular tools for genetic manipulation. Molecular technologies developed for the transformation of H. capsulatum were adapted for use in E. africanus. Agrobacterium-mediated transformation was used to generate a reporter strain expressing green fluorescent protein (GFP). The E. africanus GFP reporter strain facilitated the study of yeast interaction with macrophages in vitro and allowed the identification of infected phagocyte cell types in the mouse lung by flow cytometry. E. africanus could also maintain episomal plasmids with telomere-like sequences to introduce expression constructs without genome modification. Using this plasmid system, RNA interference constructs were used to knock down the expression of cell wall α(1,3)-glucan by targeting the transcripts of the α-glucan synthase (AGS1). An episomal CRISPR/Cas9 system was evaluated for E. africanus, which effectively disrupted GFP in a reporter strain and enabled the generation of a URA5 uracil auxotroph. These tools and strains will facilitate future studies to elucidate the mechanisms of pathogenesis of E. africanus.