Sublethal Concentration of Chloramphenicol Threatens the Health of Bombus terrestris by Regulating Gene Expression, Altering Enzyme Activity and Disrupting Gut Microbiota.

Bumblebees are dominant pollinators threatened by environmental antibiotic residues. This study investigated sublethal chloramphenicol (12 and 120 μg/L) effects on Bombus terrestris after 15 days' exposure. The results showed that chloramphenicol exposure had no significant effect on the survival rate and cumulative food intake of bumblebees, confirming the sublethal property of the tested concentrations. However, chloramphenicol significantly dysregulated the expression of genes related to learning-memory (DopR2, Oamb, NMDA), immunity (abaecin, defensin) and detoxification (cyp9Q6) in bumblebees. High-dose chloramphenicol significantly increased carboxylesterase activity and reduced malondialdehyde content, while superoxide dismutase activity remained unchanged. In addition, chloramphenicol exposure significantly reshaped the gut microbiota structure of bumblebees, reduced the abundance of core beneficial symbiotic bacteria, and increased the proportion of drug-resistant bacteria. Our findings indicate that sublethal concentrations of chloramphenicol can impair bumblebee health through multiple pathways, including regulating gene expression, altering antioxidant enzyme activity and disrupting gut microbiota homeostasis. This study provides multi-dimensional toxicological data and a scientific basis for the ecological risk assessment of agricultural antibiotic residues to pollinator insects.