Insights into the Structural and Proteomic Changes in Eimeria tenella Unsporulated Oocysts Treated with Sodium Hypochlorite

Sodium hypochlorite (NaClO) is widely used to purify oocysts in laboratories. While previous studies have extensively examined its effects on oocyst viability, pathogenicity, and sporulation rate, the impact of NaClO treatment on proteomic profiles remains uncharacterized. Transmission electron microscopy was used in the present study to characterize structural changes in unsporulated oocyst walls of <i>Eimeria tenella</i> treated with NaClO. The results indicated that NaClO treatment destroyed the bilayer wall of unsporulated oocysts, stripping away the outer wall and making the inner layer thicker. Label-free quantitative proteomics was employed to identify differentially expressed proteins (DEPs) in NaClO-treated (Et-T) and untreated (Et-C) unsporulated oocysts. Among 2422 identified proteins, 1345 were differentially expressed, with 1210 upregulated and 134 downregulated in Et-T vs. Et-C. Functional analysis revealed that upregulated proteins are predominantly associated with oocyst wall biosynthesis and cellular stress responses, whereas downregulated proteins are involved in outer wall assembly and structural integrity. Notably, 12 proteins-including 9 hypothetical proteins, acid phosphatase, adenylate cyclase, and microneme protein 2-were exclusively detected in the Et-C, indicating their potential essentiality in outer wall formation. These findings reveal the structure and protein composition of the oocyst wall of <i>E. tenella</i>, supporting research on its biosynthesis and environmental resilience.