Glycolytic Function is Necessary for iCryptococcus neoformans/i Virulence

Cryptococcus neoformans is an important fungal pathogen of immunocompromised individuals, with a close relative - C. gattii - emerging as a serious threat for the immunocompetent.  During active infection, C. neoformans colonizes the airspaces of the lungs resulting in pneumonia, and subsequently migrates to the central nervous system (CNS).  The fungus persists in the cerebrospinal fluid (CSF), and causes meningoencephalitis that is fatal if untreated.  Since C. neoformans colonizes these fundamentally different niches within the host, we sought to understand fungal carbon utilization during infection, and in particular the role of glycolysis in this model fungal pathogen.  We created mutants at either end of the glycolytic metabolic pathway, which are restricted for growth on glucose.  A pyruvate kinase mutant ( pyk1∆ ) and a hexose kinase I & II double mutant ( hxk1∆/hxk2∆ ) were made and evaluated for virulence in both rabbit-CSF and murine-inhalation models of cryptococcosis.  Results show that both mutations blocking glucose utilization result in complete attenuation of disease in both animal models.  Since the pyk1∆ mutant cannot utilize lactate for growth when glucose is present, we made a pyk1∆/mig1∆ double mutant lacking the glucose catabolite repressor MIG1.  This double mutant should be able to utilize all carbon sources available, yet it exhibited greater reduction in CSF persistence in the rabbit model compared to the pyk1∆ single mutant and was also attenuated in the mouse model.  These data suggest that energy production from glucose in various host contexts is crucial for virulence in C. neoformans .