Abstract
In this study, the addition of sulfamethazine (SMT) to landfill refuse decreased nitrogen intermediates (e.g. N2O and NO) and dinitrogen (N2) gas fluxes to <0.5 μg-N/kg-refuse·h−1, while the N2O 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 NOx 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.
Highlights
Recent worldwide studies show that at least 56 antibiotics belonging to six different classes were frequently detected from domestic wastes sources[19]
It is reasonable to hypothesize that the acquisition of antibiotic resistance genes (ARGs) may reduce the pressure/ inhibition affected by antibiotics on denitrifying bacteria or even potentially facilitate the denitrification process because some antibiotics can be utilized as carbon sources by the resistant strains[25]
Denitrification could be partially streamlined with long-term incubation, which can be more pronouncedly reflected in the SMT group
Summary
Recent worldwide studies show that at least 56 antibiotics belonging to six different classes were frequently detected from domestic wastes sources[19]. Nitrogen oxide respiration is a commonly existing physiology to increase the survival chances of microorganisms in soils[26], and this process is facilitated by diverse microorganisms with complete or partial enzymatic machinery: nitrate (nar and/ or nap), nitrite (nir), nitric oxide (nor), and nitrous oxide (nos) reduction. This enzymatic machinery may imply that higher bacterial diversity with denitrification redundancy could be more tolerant to antibiotics and possess higher intrinsic nitrogen metabolic capacity[27,28,29]. Metagenomics was employed to show the variation of ARGs and denitrification gene abundance and shifts in the microbial community under different incubation conditions with the measurement of two nitrogen oxide gases (NO and N2O) and dinitrogen (N2) gas
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