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

## TL;DR

This study reveals how sodium hypochlorite affects the structure and protein composition of Eimeria tenella oocysts, offering new insights into their wall biosynthesis and resilience.

## Contribution

The study provides the first proteomic analysis of Eimeria tenella oocysts treated with sodium hypochlorite, identifying key proteins involved in wall structure and stress response.

## Key findings

- Sodium hypochlorite treatment disrupts the oocyst wall bilayer by removing the outer layer and thickening the inner layer.
- 1345 differentially expressed proteins were identified, with upregulated proteins linked to wall biosynthesis and stress responses.
- Twelve proteins, including nine hypothetical ones, were uniquely detected in untreated oocysts, suggesting roles in outer wall formation.

## Abstract

Sodium hypochlorite (NaClO) is widely used for oocyst purification, yet the effect of NaClO on oocyst proteomic changes has not been reported. This study investigated the structural and proteomic alterations in Eimeria tenella unsporulated oocysts induced by NaClO treatment. Transmission electron microscopy revealed that NaClO disrupts the oocyst wall bilayer by removing the outer layer and inducing thickening of the inner layer. Label-free quantitative proteomics identified 1344 differentially expressed proteins (DEPs) between the NaClO-treated (Et-T) and the untreated (Et-C) unsporulated oocysts. Functional analysis showed that DEPs are primarily associated with oocyst wall biosynthesis, stress response pathways, outer wall formation, and structural integrity. These findings provide critical insights into the molecular architecture of the oocyst wall and establish a foundation for elucidating the mechanisms underlying its biosynthesis and environmental resilience.

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 Eimeria tenella 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 E. tenella, supporting research on its biosynthesis and environmental resilience.