Investigation Of Physiological Effects Of Tetracyclines On Microcystis Aeruginosa

Antibiotics have been commonly detected in aquatic ecosystems. These substances may elicit toxic effects on aquatic organisms. Furthermore, harmful algal blooms caused by cyanobacteria have threatened not only humans but also the environment. However, limited information is available regarding antibiotic toxicity to cyanobacteria. This study aimed to evaluate the toxic effects of three typical tetracycline antibiotics (tetracycline, chlotetracycline, and oxytetracycline) on Microcystis aeruginosa. Cell count, chlorophyll a and protein contents, and enzymatic antioxidant activities were determined. Results suggested that the three tetracyclines significantly inhibited cell growth at low doses. Chlorophyll a and protein contents significantly decreased after the cells were cultured with 0.05 mg/L of each antibiotic for 9 d. Superoxide dismutase (SOD) activity increased, but peroxidase (POD) and catalase (CAT) activities decreased after M. aeruginosa was exposed to 0.2 mg/L to 1 mg/L tetracycline. By contrast, SOD activity decreased, but POD and CAT activities increased after M. aeruginosa was exposed to oxytetracycline and chlotetracycline at different concentrations ranging from 0.2 mg/L to 1 mg/L and from 0.01 mg/L to 0.05 mg/L. These findings indicated that tetracycline antibiotics influenced cell growth and protein synthesis; these antibiotics also induced oxidative stress in M. aeruginosa at environmental concentrations. Thus, this study may provide further insights into the toxic effects of tetracycline antibiotics and the controlled use of antibiotics. Obviously, three antibiotics play a catalytic role in synthesis of MC-LR, the strongest degree of tetracycline, oxytetracycline followed, and chlortetracycline weakest. Besides, the synthesis of MC-RR are also influenced by three antibiotics, oxytetracycline with strongest degree and chlortetracycline with weakest degree. Thus, this study may provide further insights into the toxic effects of tetracycline antibiotics and the controlled use of antibiotics.