Effects Of Three Antibiotics On Nitrification And The Growth And Community Structure Of Ammonia-Oxidizing Microorganism In Freshwater Aquaculture Pond Sediment

High concentration of ammonia-nitrogen has been a serious obstruct to the development of Aquaculture. Ammonia-oxidizing bacteria(AOB) plays an essential role in removing ammonia-nitrogen from the water, by transforming ammonia to nitrite. In recent years, another kind of ammonia-oxidizing microorganism—Ammonia-oxidizing archaea (AOA)—was discovered, and many study results showed that it was predomiant both quantitively and actively in many ecosystems. It is presumed that AOA has made greater contribution to the biogeochemical circulation of N in some ecosystems. Abuse of fishery drugs is a burning question in aquaculture, and the environmental problems caused by antibiotics, refractory organics, are becoming increasingly evident. We chose chloramphenicol, enrofloxacin, sulfadiazine as representation of chloramphenicol drugs, sulpha drugs, and quinolones drugs respectively in this paper to study their effects on the abuandance and community structure of AOA and AOB by molecular techniques such as real-time PCR(Polymerase Chain Reaction)and denaturing gradient gel electrophoresis (DGGE). The concentration of NH4+-N, NO2--N, NO3--N were also tested to characterize the influence of those drugs on nitrification. The main conclusions were as follows:(1) Chloramphenicol of all concentrations (50mg/kg,100mg/kg,200mg/kg,500mg/kg) inhibited nitrification significantly, and showed dose-dependent effects, with group of500mg/kg chloramphenicol inhibited nitrification dramatically stronger and longer than any other groups. Under the influence of chloramphenicol, AOB’s community structure changed and it’s quantity fluctuated irregularly; while AOA’s quantity increased and it’s community structure kept stable.(2) All concentrations of enrofloxacin except50mg/kg(100mg/kg,200mg/kg,400mg/kg) inhibited nitrification process significantly for no more than one week, no dose-dependent effect was observed. Both the quantity of AOA and AOB decrease during the first week of incubation period, while neither the community structure of AOA nor that of AOB changed significantly.(3) All groups with sulfadiazine(100mg/kg,200mg/kg,500mg/kg)inhibited nitrification significantly. Sulfadiazine showed it’s effect slowly, with no obvious change in the concentration of NO2--N and NO3--N observed until two weeks of incubation. The quantity of AOB was decreased by sulfadiazine and its community structure was left undisturbed, while Both AOA’s quantity and its community structure were changed in a positive way.