Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
mSphere. 2019 Oct 9;4(5):e00644-19. doi: 10.1128/mSphere.00644-19.
R265 is a hypervirulent fungal strain responsible for the recent outbreak of cryptococcosis in Vancouver Island of British Columbia in Canada. It differs significantly from in its natural environment, its preferred site in the mammalian host, and its pathogenesis. Our previous studies of have shown that the presence of chitosan, the deacetylated form of chitin, in the cell wall attenuates inflammatory responses in the host, while its absence induces robust immune responses, which in turn facilitate clearance of the fungus and induces a protective response. The results of the present investigation reveal that the cell wall of R265 contains a two- to threefold larger amount of chitosan than that of The genes responsible for the biosynthesis of chitosan are highly conserved in the R265 genome; the roles of the three chitin deacetylases (CDAs) have, however, been modified. To deduce their roles, single and double deletion strains and a triple deletion strain were constructed in a R265 background and were subjected to mammalian infection studies. Unlike where Cda1 has a discernible role in fungal pathogenesis, in strain R265, Cda3 is critical for virulence. Deletion of either alone or in combination with another CDA (Δ or ) or both () rendered the fungus avirulent and cleared from the infected host. Moreover, the ΔΔΔ strain of R265 induced a protective response to a subsequent infection with R265. These studies begin to illuminate the regulation of chitosan biosynthesis of and its subsequent effect on fungal virulence. The fungal cell wall is an essential organelle whose components provide the first line of defense against host-induced antifungal activity. Chitosan is one of the carbohydrate polymers in the cell wall that significantly affects the outcome of host-pathogen interaction. Chitosan-deficient strains are avirulent, implicating chitosan as a critical virulence factor. R265 is an important fungal pathogen of concern due to its ability to cause infections in individuals with no apparent immune dysfunction and an increasing geographical distribution. Characterization of the fungal cell wall and understanding the contribution of individual molecules of the cell wall matrix to fungal pathogenesis offer new therapeutic avenues for intervention. In this report, we show that the R265 strain has evolved alternate regulation of chitosan biosynthesis under both laboratory growth conditions and during mammalian infection compared to that of .
R265 是一种高毒力的真菌菌株，导致了加拿大不列颠哥伦比亚省温哥华岛最近爆发的隐球菌病。它在其自然环境、在哺乳动物宿主中的首选部位和发病机制方面与 有显著差异。我们之前对 的研究表明，细胞壁中壳聚糖的存在（几丁质的去乙酰化形式）可减弱宿主中的炎症反应，而其缺失则会诱导强烈的免疫反应，进而促进真菌的清除并诱导保护性反应。本研究的结果表明，R265 的细胞壁中壳聚糖的含量是 的两倍到三倍。负责壳聚糖生物合成的基因在 R265 基因组中高度保守；然而，三个几丁质脱乙酰酶（CDAs）的作用已被修饰。为了推断它们的作用，在 R265 背景下构建了单基因和双基因缺失菌株以及三基因缺失菌株，并进行了哺乳动物感染研究。与 中 Cda1 在真菌发病机制中具有明显作用不同，在 R265 菌株中，Cda3 对毒力至关重要。单独缺失 或与另一个 CDA（Δ 或 ）组合缺失或两者都缺失（ΔΔ）会使真菌丧失毒力并从感染宿主中清除。此外，R265 的 ΔΔΔ 菌株会诱导对随后感染 R265 的保护性反应。这些研究开始阐明 中壳聚糖生物合成的调控及其对真菌毒力的后续影响。真菌细胞壁是一个重要的细胞器，其成分提供了抵御宿主诱导的抗真菌活性的第一道防线。壳聚糖是细胞壁中的碳水化合物聚合物之一，它显著影响宿主-病原体相互作用的结果。壳聚糖缺失菌株无致病性，表明壳聚糖是一个关键的毒力因子。R265 是一种重要的真菌病原体，因为它能够引起无明显免疫功能障碍个体的感染，并且其地理分布正在扩大。对真菌细胞壁的特性进行表征，并了解细胞壁基质中单个分子对真菌发病机制的贡献，为干预提供了新的治疗途径。在本报告中，我们表明与 相比，R265 菌株在实验室生长条件下和哺乳动物感染期间，壳聚糖生物合成的调节发生了进化性改变。
