Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA.
Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
mSphere. 2018 Nov 7;3(6):e00534-18. doi: 10.1128/mSphere.00534-18.
is an environmental pathogenic fungus with a worldwide geographical distribution that is responsible for hundreds of thousands of 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 of and , we evaluated the cell density of using Percoll isopycnic gradients. We found differences in the cell densities of strains belonging to and species complexes. The buoyancy of strains varied depending on growth medium. In minimal medium, the cryptococcal capsule made a major contribution to the cell density such that cells with larger capsules had lower density than those with smaller capsules. Removing the capsule, by chemical or mechanical methods, increased the cell density and reduced buoyancy. Melanization of the cell wall, which also contributes to virulence, produced a small but consistent increase in cell density. Encapsulated sedimented much more slowly 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. The buoyancy of a microbial cell is an important physical characteristic that may affect its transportability in fluids and interactions with tissues during infection. The polysaccharide capsule surrounding is required for infection and dissemination in the host. Our results indicate that the capsule has a significant effect on reducing cryptococcal cell density, altering its sedimentation in seawater. Modulation of microbial cell density via encapsulation may facilitate dispersal for other important encapsulated pathogens.
新型隐球菌是一种具有全球地理分布的环境致病真菌，每年导致数十万人患有 cryptococcosis。在感染过程中，酵母经历了形态转化，包括囊的扩大，从而增加了微生物的体积。为了了解在环境中传播的因素 和 ，我们使用 Percoll 等密度梯度评估了 的细胞密度。我们发现属于 和 种复合物的菌株的细胞密度存在差异。 的浮力取决于生长培养基。在最低培养基中，隐球菌囊对细胞密度有很大贡献，因此具有较大囊的细胞比具有较小囊的细胞密度低。通过化学或机械方法去除囊会增加 细胞密度并降低浮力。 细胞壁的黑化也有助于毒力，会导致细胞密度略有增加。被包裹的 在海水中沉降得更慢，因为其密度接近水的密度。我们的结果表明，囊可以作为一种浮选装置，有助于在水相流体中运输和分散。微生物细胞的浮力是一个重要的物理特性，可能会影响其在流体中的可运输性以及在感染过程中与组织的相互作用。包裹 的多糖囊是感染和在宿主中传播所必需的。我们的结果表明，囊对降低隐球菌细胞密度有显著影响，改变了其在海水中的沉降。通过包裹来调节微生物细胞密度可能会促进其他重要的包裹病原体的传播。
