Microsporidia are obligate intracellular parasites that infect a wide variety of host organisms, including humans. The sporoplasm is the initial stage of microsporidian infection and proliferation, but its morphological and molecular characteristics are poorly understood. In this study, the sporoplasm of Nosema bombycis was successfully isolated and characterized after the induction of spore germination in vitro The sporoplasm was spherical, 3.64 ± 0.41 μm in diameter, had the typical two nuclei, and was nonrefractive. Scanning and transmission electron microscopy analyses revealed that the sporoplasm was surrounded by a single membrane, and the cytoplasm was usually filled with relatively homogeneous granules, possibly ribosomes, and contained a vesicular structure comprising a concentric ring and coiled tubules. Propidium iodide staining revealed that the sporoplasm membrane showed stronger membrane permeability than did the cell plasma membrane. Transmission electron microscopy (TEM) revealed that the sporoplasm can gain entry to the host cell by phagocytosis. Transcriptome analysis of mature spores and sporoplasms showed that 541 significantly differentially expressed genes were screened (adjusted P value [P adj] < 0.05), of which 302 genes were upregulated and 239 genes were downregulated in the sporoplasm. The majority of the genes involved in trehalose synthesis metabolism, glycolysis, and the pentose phosphate pathway were downregulated, whereas 10 transporter genes were upregulated, suggesting that the sporoplasm may inhibit its own carbon metabolic activity and obtain the substances required for proliferation through transporter proteins. This study represents the first comprehensive and in-depth investigation of the sporoplasm at the morphological and molecular levels and provides novel insights into the biology of microsporidia and their infection mechanism.IMPORTANCE Once awoken from dormancy, the cellular matter of microsporidia is delivered directly into the host cell cytoplasm through the polar tube. This means that the microsporidia are difficult to study biologically in their active state without a contaminating signal from the host cell. Sporoplasm is a cell type of microsporidia in vitro, but relatively little attention has been paid to the sporoplasm in the past 150 years due to a lack of an effective separation method. Nosema bombycis, the first reported microsporidium, is a type of obligate intracellular parasite that infects silkworms and can be induced to germinate in alkaline solution in vitro We successfully separated the N. bombycis sporoplasm in vitro, and the morphological and structural characteristics were investigated. These results provide important insight into the biology and pathogenesis of microsporidia and potentially provide a possible strategy for genetic manipulation of microsporidia targeting the sporoplasm.

中文翻译：

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Nosema bombycis孢子质的形态学和转录组分析以及对小孢子虫的初始感染的认识。

微孢子虫是专性的细胞内寄生虫，可感染包括人类在内的多种宿主生物。孢子体是微孢子虫感染和增殖的初始阶段，但对其形态和分子特征了解甚少。在这项研究中，成功​​地分离出了Nosema bombycis的孢子体，并在体外诱导孢子萌发后对其进行了表征。孢子体是球形的，直径为3.64±0.41μm，具有典型的两个核，并且是非折射的。扫描和透射电子显微镜分析显示，孢子质被单个膜包围，细胞质通常充满相对均质的颗粒，可能是核糖体，并包含一个由同心环和盘绕的小管组成的囊状结构。碘化丙锭染色表明，孢子质膜的渗透性比细胞质膜强。透射电子显微镜（TEM）显示，孢子体可通过吞噬作用进入宿主细胞。对成熟孢子和子质进行的转录组分析表明，筛选出541个显着差异表达的基因（校正后的P值[P adj] <0.05），其中子质中有302个基因被上调，而239个基因被下调。与海藻糖合成代谢，糖酵解和磷酸戊糖途径有关的大多数基因被下调，而十个转运蛋白基因被上调，这表明孢子质可能抑制其自身的碳代谢活性并通过转运蛋白获得增殖所需的物质。这项研究代表了对孢子体形态和分子水平的首次全面，深入的研究，并为微孢子虫的生物学及其感染机制提供了新颖的见解。重要事项一旦休眠，微孢子虫的细胞物质将被直接递送到小孢子虫中。寄主细胞质通过极管。这意味着在没有来自宿主细胞的污染信号的情况下，很难在其活动状态下对微孢子虫进行生物学研究。孢子体是体外微孢子虫的一种细胞类型，但是由于缺乏有效的分离方法，在过去的150年中孢子体很少受到关注。Nosema bombycis，第一个报道的微孢子虫，是一种专一的细胞内寄生虫，可感染家蚕，可在碱性溶液中诱导萌发。我们在体外成功分离了弹状猪孢子孢子，并对其形态和结构特征进行了研究。这些结果为微孢子虫的生物学和发病机理提供了重要的见解，并可能为针对孢子质的微孢子虫的遗传操作提供可能的策略。