Resumo

Cryptococcus neoformans causes a life threatening fungal meningitis in immunocompromised patients. This fungal pathogen is associated with high mortality rates and has been identified as the most fatal agent of systemic mycoses in AIDS patients. The most prominent morphological characteristic of C. neoformans is the presence of a polysaccharide capsule, which is attached to cell wall and entraps divalent cations including calcium and magnesium. These ions are required for capsular enlargement, a determinant factor for fungal pathogenesis. Therefore, mechanisms involved in the regulation of the concentration of divalent cations at the cell surface are likely essential for fungal pathogenesis. These putative mechanisms are still unknown in the C. neoformans model. Acidocalcisomes are calcium storage acidic organelles that contain several polyphosphate-bound cations. These organelles have been described in a variety of organisms. Acidocalcisomes are acidified through the action of proton pumps such as the vacuolar proton ATPase and the vacuolar proton pyrophosphatase. As described in other microorganisms, polyphosphates can also participate in ion homeostasis. In this study, we analyzed the presence of polyphosphate-rich organelles in C. neoformans. By using fluorescence microscopy, cell wall-associated polyphosphates were observed after staining fungal cells with DAPI. Intracellular polyP stocks were also observed in C. neoformans. Short-chain and long-chain polyphosphates were extracted from yeast cells and the amount of inorganic phosphate was determined spectrophotometrically after treatment of the polyphosphate fractions with an S. cerevisiae polyphosphatase (PPX1). The identification of cell wall polyphosphates in C. neoformans may lead to future studies involving their participation in capsular architecture and ion homeostasis. Considering the essential role of the cryptococcal capsule in fungal pathogenesis, surface-associated polyphosphates might also interfere with the interaction of C. neoformans with host cells.