Screens of C. albicans deletion collections in the murine reveals role for filamentation transcription factors

Candida albicans is a human gut commensal and an opportunistic pathogen. The ability to transition from yeasts to invasive hyphae is a central virulence attribute, but it is unclear how these two cell types function during commensal growth.  Using FISH to visualize C. albicans in a murine gut colonization model, we observed the co-occurrence of yeasts and hyphae throughout the gastrointestinal tract. Forward genetic analysis revealed that major transcriptional activators of yeast-to-hypha morphogenesis have unexpected activity as potent inhibitors of commensalism.  In vivo FISH, transcriptomic, and genetic analyses indicate that the morphogenesis program inhibits commensal fitness, not through control of cell shape as expected from in vitro studies, but by activating expression of a hypha-specific pro-inflammatory secreted protease and a hyphal cell surface adhesin. These results reveal a tradeoff between fungal programs supporting commensalism and virulence within the commensal niche in which selection against hypha-specific markers limits the disease-causing potential of this ubiquitous commensal-pathogen. Overall design: Pooled mutants from isogenic knockout collections were screened for commensal fitness in a mouse model of murine gastrointestinal colonization