Regulation Effects And Mechanisms Of Mixed Antibiotics In Microcystis Aeruginosa Exposed To Ultraviolet Radiation

Antibiotic contamination has become a serious environmental problem due to the broad use and discharge of antibiotics.Various antibiotic contaminants are simultaneously detected in aquatic environments,and cyanobacteria are exposed to mixed antibiotics.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.In this study,UV radiation(UV-B and UV-C)was selected as the typical cyanobacterial control technology,and Microcystis aerugi'nosa was selected as the model cyanobacterial species,investigated regulation effects and mechanisms of mixed antibiotics(amoxicillin,tetracycline,spiramycin,ciprofloxacin and sulfamethoxazole)in M.aeruginosa exposed to UV-B and UV-C radiation at their current contamination level of 200 ng L-1.Mixed antibiotics alleviated the 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.Mixed antibiotics can stimulate the synthesis of chlorophyll a in M.aeruginosa exposed to UV-B and low radiation dose of UV-C.At the highest dose of UV-C radiation(240 mJ cm-2),antibiotics inhibited the synthesis of chlorophyll-a in UV-C treated M.aeruginosa.Mixed antibiotics may regulate the toxicity of UV radiation via the photosynthesis process,according to the responses of chlorophyll-a.UV radiation stimulated the synthesis of microcystins,which was further enhanced by mixed antibiotics.Increased synthesis of microcystins led to an increased threaten to the aquatic environment.Responses of superoxide dismutase to UV radiation and mixed antibiotics were in accordance with that of growth rate and cell density,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.The presence of mixed antibiotics enhanced the toxicity of UV-C to M.aeruginosa at radiation dose of 240 mJ cm-2.Mixed antibiotics may be degraded at the highest UV-C dose,and degradation products may be responsible for the enhancement of UV-C toxicity.The response of proteome further indicated that both UV-B and UV-C radiation inhibited the growth of M.aeruginosa through the photosynthesis system.Antibiotics can reduce the toxicity of UV-B by regulating the nitrogen metabolism-related proteins.The toxicity of UV-C at radiation dose of 48-144 mJ cm-2 can be alleviated by antibiotics through the stimulation of photosynthesis-related proteins.With the co-existence of antibiotic contaminants,the radiation dose should be increased during the treatment of M.aeruginosa by UV treatment.