The buoyant cell density ofCryptococcus neoformansis affected by capsule size

Abstract

AbstractCryptococcus neoformansis an environmental pathogenic fungus with a worldwide geographical distribution that is responsible for hundreds of thousands human cryptococcosis cases each year. During infection, the yeast undergoes a morphological transformation involving capsular enlargement that increases microbial volume. To understand the factors that play a role in environmental dispersal ofC. neoformansandC. gatiiwe evaluated the buoyant cell density ofCryptococcususing Percoll isopycnic gradients. We found differences in the buoyant cell density of strains belonging toC. neoformansandC. gattispecies complexes. The buoyant cell density ofC. neoformansstrains varied depending on growth medium conditions. In minimal medium, the cryptococcal capsule made a major contribution to the buoyant cell density such that cells with larger capsules had lower density than those with smaller capsules. Removing the capsule, both by chemical or mechanical methods, decreased theC. neoformanscell density. Melanization of theC. neoformanscell wall, which also contributes to virulence, produced a small but consistent increase in cell density.C. neoformanssedimented much slower in seawater as its density approached the density of water. Our results suggest a new function for the capsule whereby it can function as a flotation device to facilitate transport and dispersion in aqueous fluids.