Synergetic effect of antibiotic mixtures on soil bacterial N 2 O-reducing communities
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ORIGINAL PAPER
Synergetic effect of antibiotic mixtures on soil bacterial N2O‑reducing communities Céline Roose‑Amsaleg1,2 · Viviane David2,3 · Fabrice Alliot2 · Elodie Guigon2 · Olivier Crouzet3 · Anniet M. Laverman1 Received: 4 May 2020 / Accepted: 8 October 2020 © Springer Nature Switzerland AG 2020
Abstract Antibiotics released in agricultural soils alter soil bacterial communities, inducing antimicrobial resistance and, in turn, canceling the efficiency of antibiotic drugs used for human and animal health. In soils, antibiotic impact on nitrogen cycling is poorly known, notably when antibiotic mixtures are applied. We hypothesized that the impact of antibiotic mixtures would have higher effects on denitrification. We exposed soil denitrifying bacteria enrichments to tetracycline, ofloxacin, sulfamethoxazole and tylosin, either applied single or as mixture of three antibiotics, during 7 days under denitrifying conditions. We measured the minimum inhibitory concentration of the N 2O-reducing capacity of the bacterial enrichment, we deduced the half maximal effective concentration ( EC50) from the experimental data and from the concentration addition hypothesis, and we quantified nosZ gene abundances. Results show that single antibiotic exposure inhibited N2O-reduction only for tetracycline at 64 mg/L. Inhibition by antibiotic mixtures always exceeded the modeled inhibition calculated by concentration addition. At high-antibiotic exposure, nosZ gene clade I denitrifiers remained abundant, of 1 07–108 copies/ ng DNA. NosZ gene clade II denitrifiers increased with antibiotic concentrations. Our findings reveal for the first time the synergistic effects of antibiotic mixtures on soil nitrogen cycling. Keywords Antibiotic mixture · Denitrification · N2O-reducing community · Soil · Microbial ecotoxicology
Introduction Soils are among the most antibiotic-contaminated environments with concentrations ranging from a few nanograms to milligrams per kg, resulting from organic waste recycling or waste water irrigation of urban or agricultural origin (Cycon et al. 2019; Daghrir and Drogui 2013). Soil bacteria are thus chronically exposed to numerous antibiotics (Tijani Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10311-020-01117-3) contains supplementary material, which is available to authorized users. * Céline Roose‑Amsaleg celine.amsaleg@univ‑rennes1.fr 1
CNRS, ECOBIO ‑ UMR 6553, Univ Rennes 1, 35000 Rennes, France
2
CNRS, EPHE, PSL University, METIS ‑ UMR 7619, Sorbonne Universités, 75005 Paris, France
3
UMR ECOSYS, INRA, AgroParisTech, Université Paris-Saclay, 78026 Versailles, France
et al. 2016), possibly affecting their growth, activity, community structure and biogeochemical cycling (DeVries and Zhang 2016; Roose-Amsaleg and Laverman 2016). However, while soils accumulate many antimicrobial molecules having different mechanisms of action, the co-occurrence of contaminants in mixtures remains largely unconsidered in microbial ecotoxicolo
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