The transcription factor Ndt80 is a repressor of Candida parapsilosis virulence attributes

<i>Candida parapsilosis</i> is an emergent opportunistic yeast among hospital settings that affects mainly neonates and immunocompromised patients. Its most remarkable virulence traits are the ability to adhere to prosthetic materials, as well as the formation of biofilm on abiotic surfaces. The Ndt80 transcription factor was identified as one of the regulators of biofilm formation by <i>C. parapsilosis</i>; however, its function in this process was not yet clarified. By knocking out <i>NDT80</i> (<i>CPAR2-213640</i>) gene, or even just one single copy of the gene, we observed substantial alterations of virulence attributes, including morphogenetic changes, adhesion and biofilm growth profiles. Both <i>ndt80Δ</i> and <i>ndt80ΔΔ</i> mutants changed colony and cell morphologies from smooth, yeast-shaped to crepe and pseudohyphal elongated forms, exhibiting promoted adherence to polystyrene microspheres and notably, forming a higher amount of biofilm compared to wild-type strain. Interestingly, we identified transcription factors Ume6, Cph2, Cwh41, Ace2, Bcr1, protein kinase Mkc1 and adhesin Als7 to be under Ndt80 negative regulation, partially explaining the phenotypes displayed by the <i>ndt80ΔΔ</i> mutant. Furthermore, <i>ndt80ΔΔ</i> pseudohyphae adhered more rapidly and were more resistant to murine macrophage attack, becoming deleterious to such cells after phagocytosis. Unexpectedly, our findings provide the first evidence for a direct role of Ndt80 as a repressor of <i>C. parapsilosis</i> virulence attributes. This finding shows that <i>C. parapsilosis</i> Ndt80 functionally diverges from its homolog in the close related fungal pathogen <i>C. albicans</i>.

近平滑假丝酵母（Candida parapsilosis）是医院环境中渐趋频发的机会致病性酵母菌，主要感染新生儿与免疫功能低下患者。其最显著的毒力性状包括黏附医用植入材料的能力，以及在无生命表面形成生物被膜的特性。Ndt80转录因子（Ndt80 transcription factor）已被鉴定为近平滑假丝酵母生物被膜形成的调控因子之一，但该因子在此过程中的具体功能尚未阐明。本研究通过敲除NDT80（CPAR2-213640）基因，甚至仅敲除该基因的单个拷贝，观察到毒力相关性状发生显著改变，包括形态发生变化、黏附能力及生物被膜生长特性的改变。单敲除ndt80Δ突变株与双敲除ndt80ΔΔ突变株的菌落及细胞形态均从光滑酵母型转变为皱缩假菌丝伸长型；相较于野生型菌株，二者对聚苯乙烯微球的黏附能力增强，且生物被膜生成量显著升高。值得注意的是，本研究鉴定出转录因子Ume6、Cph2、Cwh41、Ace2、Bcr1、蛋白激酶Mkc1以及黏附素Als7均受Ndt80的负调控，这一结果部分解释了ndt80ΔΔ突变株所呈现的表型特征。此外，ndt80ΔΔ突变株的假菌丝黏附速度更快，且对小鼠巨噬细胞的杀伤抗性更强，吞噬作用后可对巨噬细胞产生有害影响。出乎意料的是，本研究首次证实Ndt80作为负调控因子直接参与近平滑假丝酵母的毒力性状调控。该研究结果表明，近平滑假丝酵母的Ndt80在功能上与其近缘真菌病原菌白色念珠菌（Candida albicans）的同源蛋白存在显著差异。