Defects in Phosphate Acquisition and Storage Influence Virulence of Cryptococcus neoformans

Abstract

ABSTRACTNutrient acquisition and sensing are critical aspects of microbial pathogenesis. Previous transcriptional profiling indicated that the fungal pathogenCryptococcus neoformans, which causes meningoencephalitis in immunocompromised individuals, encounters phosphate limitation during proliferation in phagocytic cells. We therefore tested the hypothesis that phosphate acquisition and polyphosphate metabolism are important for cryptococcal virulence. Deletion of the high-affinity uptake system interfered with growth on low-phosphate medium, perturbed the formation of virulence factors (capsule and melanin), reduced survival in macrophages, and attenuated virulence in a mouse model of cryptococcosis. Additionally, analysis of nutrient sensing functions forC. neoformansrevealed regulatory connections between phosphate acquisition and storage and the iron regulator Cir1, cyclic AMP (cAMP)-dependent protein kinase A (PKA), and the calcium-calmodulin-activated protein phosphatase calcineurin. Deletion of theVTC4gene encoding a polyphosphate polymerase blocked the ability ofC. neoformansto produce polyphosphate. Thevtc4mutant behaved like the wild-type strain in interactions with macrophages and in the mouse infection model. However, the fungal load in the lungs was significantly increased in mice infected withvtc4deletion mutants. In addition, the mutant was impaired in the ability to trigger blood coagulationin vitro, a trait associated with polyphosphate. Overall, this study reveals that phosphate uptake inC. neoformansis critical for virulence and that its regulation is integrated with key signaling pathways for nutrient sensing.