Insight into the effects of sulfamethoxazole and norfloxacin on nitrogen transformation functional genes during swine manure composting.

The effects of sulfamethoxazole and norfloxacin on nitrogen functional genes were investigated in four composting treatments of swine manure: CK (no antibiotics), SMZ (spiked with 5 mg kg-1 dry weight (DW) sulfamethoxazole), NOR (spiked with 5 mg kg-1DW norfloxacin), and SN (spiked with 5 mg kg-1DW sulfamethoxazole and 5 mg kg-1DW norfloxacin). Antibiotics decreased relative abundance of bacterial amoA and nxrA, while increased nosZ/nirK. The decline in amoA/16S rRNA increased the total NH3 emission in SMZ and NOR from 1027.05 to 1144.39 and 1278.22 mg kg-1DW. The decrease of nxrA/16S rRNA enhanced the NO2--N content and N2O emission in SMZ in the initial composting. Additionally, the increase in nosZ/nirK probably was the main reason for the lower N2O emission in SN than other treatments in the cooling phase. The inhibition on nitrification process and increase in NH3 emission resulted from antibiotics is worthy of attention in the future.