Effects of Antibiotics on the DAMO Process and Microbes in Cattle Manure

Denitrifying anaerobic methane oxidation (DAMO) can mitigate methane emissions; however, this process has not been studied in cattle manure, an important source of methane emissions in animal agriculture. The objective of this study was to investigate the occurrence of DAMO microbes in cattle manure and examine the impacts of veterinary antibiotics on the DAMO process in cattle manure. Results show that DAMO archaea and bacteria consistently occur at high concentrations in beef cattle manure. During the long-term operation of a sequencing batch reactor seeded with beef cattle manure, the DAMO activities intensified, and DAMO microbial biomass increased. Exposure to chlortetracycline at initial concentrations up to 5000 μg L^–1 did not inhibit DAMO activities or affect the concentrations of the 16S rRNA gene and functional genes of DAMO microbes. In contrast, exposure to tylosin at initial concentrations of 50 and 500 μg L^–1 increased the activities of the DAMO microbes. An initial concentration of 5000 μg L^–1 TYL almost entirely halted DAMO activities and reduced the concentrations of DAMO microbes. These results show the occurrence of DAMO microbes in cattle manure and reveal that elevated concentrations of dissolved antibiotics could inhibit the DAMO process, potentially affecting net methane emissions from cattle manure.