Effects of Bacillus amyloliquefaciens and Exiguobacterium aestuarii on the physiological and toxicological responses of the whiteleg shrimp (Litopenaeus vannamei) under acute diazinon exposure.

Organophosphate insecticides are widely used in agriculture; however, excessive application can lead to environmental contamination and toxic effects on non-target organisms. Among these compounds, diazinon exhibits high persistence and toxicity in soil and aquatic environments, necessitating the development of environmentally friendly remediation technologies. In this study, microbial community analysis was conducted to screen microorganisms capable of efficiently degrading diazinon, and Bacillus amyloliquefaciens and Exiguobacterium aestuarii with high diazinon degradation efficiency were identified. A 96-h acute toxicity test using whiteleg shrimp (Litopenaeus vannamei, 4.9 ± 1.0 g) revealed that the LC₅₀ value of diazinon was 0.073 mg/L, and a sublethal concentration (LC₂₀, 0.015 mg/L) was used for subsequent experiments. High-performance liquid chromatography (HPLC) analysis showed that approximately 72% of diazinon was rapidly degraded in the treatment group inoculated with a mixed culture of the two selected strains. In the diazinon-only exposure group, the activities of superoxide dismutase (SOD) and catalase (CAT), as well as the level of malondialdehyde (MDA), were significantly increased. Additionally, the expression of antioxidant and detoxification-related genes (SOD, CAT, GPx, and CYP450) was upregulated, while acetylcholinesterase (AChE) activity in brain was markedly inhibited, indicating pronounced oxidative stress and neurotoxicity. In contrast, shrimp exposed to diazinon in combination with the microbial treatment exhibited stable AChE activity and reduced oxidative stress indicators. These results demonstrate that mixed-strain treatment effectively mitigates the physiological and neurotoxic damage induced by diazinon. Overall, this study suggests that the combined culture of B. amyloliquefaciens and E. aestuarii enhances diazinon degradation and alleviates its toxic effects, highlighting its potential application as a biological remediation strategy in aquaculture and aquatic environments.