Effects of beta-cypermethrin on the antioxidant system and gut microbiota in Eisenia fetida

This study aimed to comprehensively assess oxidative stress responses and gut microbiota alterations in earthworms exposed to β-cypermethrin (β-CYP), and to analyze their relationship. β-CYP significantly increased malondialdehyde (MDA) content by up to 90.34% and peroxidase (POD) activity by up to 43.22% in a concentration-dependent manner (p < 0.05). Superoxide dismutase (SOD) activity was induced at 5 mg/kg but inhibited at 40 mg/kg. Although gut microbial alpha diversity showed no significant change, the composition and function were altered markedly. At the phylum level, Proteobacteria increased by 104.53%, while Actinobacteria and Firmicutes decreased by 46.30% and 61.38% at 5 mg/kg, respectively, whereas fungal communities remained stable. KEGG analysis showed that microbial functions shifted from nutrient and energy acquisition toward detoxification and pollutant resistance. Correlation analysis showed significant associations between gut microbiota and host antioxidant capacity. These findings demonstrate that β-CYP exerts concentration-dependent toxicity via oxidative damage and gut microbial dysbiosis.