Einarsson Elin, Svärd Staffan G, Troell Karin
Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden.
Department of Virology, Immunobiology and Parasitology, National Veterinary Institute, Uppsala, Sweden.
Exp Parasitol. 2015 Jul;154:25-32. doi: 10.1016/j.exppara.2015.03.024. Epub 2015 Mar 28.
The response to ultraviolet light (UV) radiation, a natural stressor to the intestinal protozoan parasite Giardia intestinalis, was studied to deepen the understanding of how the surrounding environment affects the parasite during transmission. UV radiation at 10 mJ/cm(2) kills Giardia cysts effectively whereas trophozoites and encysting parasites can recover from UV treatment at 100 mJ/cm(2) and 50 mJ/cm(2) respectively. Staining for phosphorylated histone H2A showed that UV treatment induces double-stranded DNA breaks and flow cytometry analyses revealed that UV treatment of trophozoites induces DNA replication arrest. Active DNA replication coupled to DNA repair could be an explanation to why UV light does not kill trophozoites and encysting cells as efficiently as the non-replicating cysts. We also examined UV-induced gene expression responses in both trophozoites and cysts using RNA sequencing (RNA seq). UV radiation induces small overall changes in gene expression in Giardia but cysts show a stronger response than trophozoites. Heat shock proteins, kinesins and Nek kinases are up-regulated, whereas alpha-giardins and histones are down-regulated in UV treated trophozoites. Expression of variable surface proteins (VSPs) is changed in both trophozoites and cysts. Our data show that Giardia cysts have limited ability to repair UV-induced damage and this may have implications for drinking- and waste-water treatment when setting criteria for the use of UV disinfection to ensure safe water.
为了更深入地了解周围环境在传播过程中如何影响肠道原生动物寄生虫贾第虫，研究了其对紫外线（UV）辐射这一自然应激源的反应。10 mJ/cm² 的紫外线辐射可有效杀死贾第虫包囊，而滋养体和正在形成包囊的寄生虫分别可从 100 mJ/cm² 和 50 mJ/cm² 的紫外线处理中恢复。磷酸化组蛋白 H2A 的染色显示紫外线处理会诱导双链 DNA 断裂，流式细胞术分析表明对滋养体进行紫外线处理会诱导 DNA 复制停滞。活跃的 DNA 复制与 DNA 修复相结合，可能解释了为什么紫外线不能像杀死不进行复制的包囊那样有效地杀死滋养体和正在形成包囊的细胞。我们还使用 RNA 测序（RNA seq）研究了紫外线诱导的滋养体和包囊中的基因表达反应。紫外线辐射在贾第虫中诱导基因表达发生总体较小的变化，但包囊的反应比滋养体更强。在紫外线处理的滋养体中，热休克蛋白、驱动蛋白和 Nek 激酶上调，而α-贾第蛋白和组蛋白下调。可变表面蛋白（VSP）的表达在滋养体和包囊中均发生变化。我们的数据表明，贾第虫包囊修复紫外线诱导损伤的能力有限，这可能对制定紫外线消毒标准以确保安全用水的饮用水和污水处理产生影响。
