Regulation Effects And Mechanisms Of Low Concentration Of Amoxicillin On The Bloom Of Microcystis Aeruginosa

In recent years,antibiotics have been frequently detected in surface waters due to the continuous utilization and discharge.The prokaryotic cyanobacteria were found to be sensitive to antibiotics.Consequently,antibiotic contaminants may be an emerging environmental factor regulating cyanobacterial blooms.Microcystis aeruginosa,a dominant prokaryotic species causing cyanobacterial blooms,was selected as the target species in the present study.A widely used and broadly detected antibiotic,amoxicillin,was selected as the target antibiotic.The short-term regulation effects of amoxicillin in M.aeruginosa were examined at environmentally relevant concentrations through a 7-day exposure test.A 30-day semi-continuous culture was adopted to further explore the long-term action effect and mechanism of amoxicillin in cyanobacteria.The responses of the whole proteome were examined based on a 2-DE proteomic technique.The chlorophyll-a content was significantly stimulated?p<0.05?by 100 ng/L and 300 ng/L of amoxicillin during the short-term exposure test.The expressions of three photosynthesis-related genes?psaB,psbA and rbcL?were all up-regulated by amoxicillin.Fv/Fm and rETRmax values in M.aeruginosa also increased under long-term exposure to amoxicillin.Proteins encoded by psbA,psaB and rbcL were also up-regulated.The above results proved that low concentration of coexisting amoxicillin could stimulate the photosynthesis activity in M.aeruginosa under both short-term exposure and long-term exposure.The stimulated photosynthesis activity further increased energy production and then excited another two energy-consuming responses,the growth of M.aeruginosa and the production of MCs.Amoxicillin was observed to cause hormesis effects in M.aeruginosa.The protein-protein interaction module?p<0.05?also presented a significant interaction?p<0.05?between mcyB and the universal stress protein?MAE₄8380?via the mediation of photosynthesis-related proteins,which indicated that MCs production was closely correlated with photosynthesis,and played a role in stress response to amoxicillin exposure.The activities of antioxidant enzymes?Superoxide dismutase,Peroxidase and Glutathione S-transferase?and the content of antioxidant?Glutathione?were significantly increased?p<0.05?by 100 ng/L and 300 ng/L of amoxicillin,indicating the induction of oxidative stress response in M.aeruginosa.The above results have been further proved by proteomic analysis.The up-regulated expression of superoxide dismutase,one phase I detoxification enzyme?MAE₃5830?and three phase II detoxification enzymes?MAE₁5 8 50,MAE₄6260 and MAE₁3100?proved that amoxicillin could cause oxidative stress in M.aeruginosa and trigger the detoxification process for scavenging ROS.Coexsiting amoxicillin has a potential to stimulate the bloom of M.aeruginosa at its current contamination level.