Change in microbial community in landfill refuse contaminated with antibiotics facilitates denitrification more than the increase in ARG over long-term

In this study, the addition of sulfamethazine (SMT) to landfill refuse decreased nitrogen intermediates (e.g. N₂ O and NO) and dinitrogen (N₂) gas fluxes to <0.5 μg-N/kg-refuse·h^-1, while the N₂ O and N₂ flux were at ∼1.5 and 5.0 μg-N/kg-refuse·h^-1 respectively in samples to which oxytetracycline (OTC) had been added. The ARG (antibiotic resistance gene) levels in the refuse increased tenfold after long-term exposure to antibiotics, followed by a fourfold increase in the N₂ flux, but SMT-amended samples with the largest resistome facilitated the denitrification (the nitrogen accumulated as NO gas at ∼6 μg-N/kg-refuse·h^-1) to a lesser extent than OTC-amended samples. Further, deep sequencing results show that long-term OTC exposure partially substituted Hyphomicrobium, Fulvivirga, and Caldilinea (>5%) for the dominant bacterial hosts (Rhodothermus, ∼20%) harboring nosZ and norB genes that significantly correlated with nitrogen emission pattern, while sulfamethazine amendment completely reduced the relative abundance of the "original inhabitants" functioning to produce NO x gas reduction. The main ARG carriers (Pseudomonas) that were substantially enriched in the SMT group had lower levels of denitrifying functional genes, which could imply that denitrification is influenced more by bacterial dynamics than by abundance of ARGs under antibiotic pressures.