Spiroplasma eriocheiris Enters Drosophila Schneider 2 Cells and Relies on Clathrin-Mediated Endocytosis and Macropinocytosis.

Spiroplasma eriocheiris causes great economic losses in the crustacean aquaculture industry. However, the mechanism of S. eriocheiris infecting host cells has been poorly studied. We established a Spiroplasma-infected Drosophila Schneider 2 (S2) cell model and investigated its pathogenic mechanism. First, S. eriocheiris induced S2 cell apoptosis and necrosis, seriously decreased cell viability, and increased the production of intracellular reactive oxygen species. Further research showed that S. eriocheiris can invade S2 cells, and the number of copies of intracellular spiroplasmas is sharply increased by 12 h postinfection. In addition, S. eriocheiris can cause S2 cells to form typical inclusion bodies and exhibit large vacuoles. Second, S. eriocheiris is internalized into S2 cells and strongly inhibited through blocking clathrin-mediated endocytosis using chlorpromazine and dynasore. Inhibitors of macropinocytosis, protein kinase C and myosin II, cause a significant reduction in S. eriocheiris in S2 cells. In contrast, disruption of cellular cholesterol by methyl-β-cyclodextrin and nystatin has no effect on S. eriocheiris infection. These results suggest that the entry of S. eriocheiris into S2 cells relies on clathrin-dependent endocytosis and macropinocytosis, but not via the caveola-mediated endocytic pathway. In addition, the intracellular numbers of S. eriocheiris are dramatically reduced after S2 cells are treated with cytoskeleton-depolymerizing agents, including nocodazole and cytochalasin B. Thus, cellular infection by S. eriocheiris is related to microtubules and actin filaments. This research successfully shows for the first time that S. eriocheiris can invade Drosophila S2 cells and provides a process for S. eriocheiris infection.