Antibiotic and metal resistance genes are closely linked with nitrogen-processing functions in municipal solid waste landfills.

Landfilled antibiotics and metals were related to the occurrences of their resistance genes, whose decade-long development in leachates with the dynamic landfilling environmental conditions, especially with the varying nitrogen contents, has yet to be studied. Here, we sampled leachates from five representative municipal solid waste landfills in China. The total concentrations of antibiotics (5000 - 50000 ng/L) and metals (10 - 60 mg/L) in leachates were significantly different among different sites and they were only closely related to sulfonamide and tetracycline resistance genes (P < 0.05). Regarding the abundance of subtype resistance genes, sul1 and ermB were dominant antibiotic resistance genes (ARGs) and terc, arsc, and mer were dominant heavy metal resistance genes (HMRGs); and meanwhile the observed huge variations of these genes appeared to be related to environmental factors like nitrate and pH (P < 0.05). The GeoChip results further indicated that more than 85% of sequenced ARGs/HMRGs and nitrogen processing genes, particularly of the denitrification genes, were hosted by the same bacterial species, such as Pseudomonas sp. and Bacillus sp., which belonged to the predominant phylum in leachates. These results extended our knowledge about the linkages among ARGs, HMRGs and nitrogen-processing functions in leachates.