Regulation of five-antibiotic mixture on Microcystis aeruginosa exposed to sublethal doses of ultraviolet radiation

Abstract

Previous reports suggested that coexisting antibiotics could enhance cyanobacterial growth and cyanotoxin production, but the influence of antibiotics on cyanobacterial removal has not been reported. This study investigated regulation effects and mechanisms of mixed antibiotics (ciprofloxacin, amoxicillin, sulfamethoxazole, tetracycline and spiramycin) in Microcystis aeruginosa exposed to UV-B and UV-C radiation at their current contamination level of 200 ng L−1. Mixed antibiotics alleviated growth inhibition effects of 240–480 mJ cm−2 of UV-B and 48–144 mJ cm−2 of UV-C, while enhanced the growth inhibition effects of 240 mJ cm−2 of UV-C. Responses of chlorophyll-a suggested that mixed antibiotics may regulate the toxicity of UV radiation via photosynthesis. Mixed antibiotics increased the production of microcystins in UV-treated M. aeruginosa, which may cause further hazard to the aquatic environment. Superoxide dismutase activity, growth rate and cell density varied in a similar pattern under exposure to UV radiation and mixed antibiotics, suggesting the correlation between cyanobacterial growth and reactive oxygen species during the UV treatment regulated by antibiotics. Responses of malondialdehyde suggested a higher toxicity of UV-C than UV-B to M. aeruginosa under the regulation of mixed antibiotics. With the coexistence of antibiotic contaminants, the radiation dose should be increased during the removal of M. aeruginosa by UV treatment.