Oxidative stress mechanisms underlying temporal hormesis effects induced by binary antibiotic mixtures on Scenedesmus obliquus

The hormesis effect has gradually become a research focus in environmental science and toxicology due to its unique phenomenon of low-concentration stimulation and high-concentration inhibition. The combined toxicity of antibiotics and their regulatory effects on microorganisms are areas that warrant significant attention. In this study, doxycycline hydrochloride (DXC), sulfamethoxazole (SMX) and sulfamethazine (SMZ) were used as the research objects, and Scenedesmus obliquus was used as the indicator organism to study their toxicity and action laws at different exposure times (4d and 8d). The toxic effects of antibiotic mixtures with hormesis effect on Scenedesmus obliquus were comprehensively evaluated from the aspects of growth inhibition, photosynthesis index and antioxidant enzyme activity. The results showed that 11 rays produced hormesis effect, and the hormesis effect value on the 8th day was greater than that on the 4th day. Through the prediction of combined toxicity, it was found that the type and intensity of action were affected by the mixture composition, exposure time and concentration. Hormesis is caused by the regulation of photosynthesis, the activation of the antioxidant defense system, the regulation of gene expression, and the change in cell membrane permeability. This study provides a theoretical basis for comprehensively understanding the environmental toxicity caused by antibiotic mixtures with a hormesis effect.