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Antibiotics favor the establishment of antibiotrophic bacteria in agricultural soil microbial communities, but are not always sufficient to enhance antibiotic-degradation: manure spreading can help.

Abstract : During the past decades, environmental concentrations of antibiotics have largely increased, resulting in a risk of ecosystem disturbance. However, because their composition is often rich in nitrogen and carbon, antibiotics are of nutritional interest for microorganisms, as long as their biocidal character is not considered. Antibiotic-degrading bacteria have therefore emerged amongst strains that were resistant to antibiotics. Called antibiotrophs, they are able to use selected antibiotics as nutritive sources for their growth. While several antibiotrophs have been isolated from different agroecosystems, little is known about their ecology. In particular, their dispersal capacity is poorly evaluated, even though manure spreading is a suspected source of antibiotrophs for agroecosystems. Also, their antibiotic degradation ability in complex agricultural soil communities remains insufficiently studied. In this context, a microcosm experiment was set up by inoculating the sulfonamide-degrading and resistant bacterium, Microbacterium sp. C448, in four different soil types supplied or not with sulfamethazine and/or swine manure. After one month of incubation, qPCR analyses and 16S rDNA sequencing were performed to respectively quantify the inoculated strain, its antibiotrophic gene sadA, and to characterize the structure of bacterial communities. In parallel, a similar experiment was carried out with the addition of radiolabeled sulfamethazine, in order to monitored antibiotrophy activity during incubation by radiorespirometry. Quantitative PCR results showed an effective establishment of the strain and its sulfamethazinedegrading gene (sadA) only under sulfamethazine selection pressure. This reflects the low competitiveness of the strain, which possesses a low invasion potential under non-antibiotic contaminated conditions. Sulfamethazine treated soils differed in their capacity to mineralize the antibiotic. Indeed, in absence of manure and despite the presence of Microbacterium sp. C448, only one of the four tested soils exhibited slight mineralization capacities. Whatever the soil type, radiorespirometry analyses showed that manure addition significantly enhanced sulfamethazine mineralization. These results confirm that the presence of functional genes does not necessarily ensure functionality. Moreover, they suggest that sulfamethazine does not necessarily confer a selective advantage to the degrading strain, as a nutritional source. In addition, 16S rDNA sequencing analyses strongly suggest that sulfamethazine has released trophic niches by biocidal action. Accordingly, manure-originating bacteria and/or Microbacterium sp C448 could have access to low competition or competition-free trophic niches. However, simultaneous inputs of manure and of the strain could induce detrimental competition for Microbacterium sp. C448, thus forcing it to use sulfamethazine as a nutritional source. Altogether, these results suggest that the studied antibiotrophic strain can modulate its sulfamethazine-degradation function depending on microbial competition and resource accessibility, to establish in an agricultural soil. Most importantly, this work highlights an increased dispersal potential of antibiotrophs in antibiotic-polluted environments, as antibiotics can not only release existing trophic niches but also constitute new ones.
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Conference papers
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https://hal.inrae.fr/hal-03105782
Contributor : Noureddine El Mjiyad <>
Submitted on : Monday, January 11, 2021 - 12:48:53 PM
Last modification on : Thursday, March 4, 2021 - 11:04:07 AM

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  • HAL Id : hal-03105782, version 1

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Loren Billet, Stéphane Pesce, Nadine Rouard, Aymé Spor, Laurent Fabrice Martin, et al.. Antibiotics favor the establishment of antibiotrophic bacteria in agricultural soil microbial communities, but are not always sufficient to enhance antibiotic-degradation: manure spreading can help.. EcotoxicoMic 2020, 2nd International Conference on Microbial Ecotoxicology, Oct 2020, Dijon, France. ⟨hal-03105782⟩

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