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 innitrogen and carbon, antibiotics are of nutritional interest for microorganisms, as long as theirbiocidal character is not considered. Antibiotic-degrading bacteria have therefore emerged amongststrains that were resistant to antibiotics. Called antibiotrophs, they are able to use selectedantibiotics as nutritive sources for their growth. While several antibiotrophs have been isolated fromdifferent agroecosystems, little is known about their ecology. In particular, their dispersal capacity ispoorly evaluated, even though manure spreading is a suspected source of antibiotrophs foragroecosystems. Also, their antibiotic degradation ability in complex agricultural soil communitiesremains insufficiently studied.In this context, a microcosm experiment was set up by inoculating the sulfonamide-degrading andresistant bacterium, Microbacterium sp. C448, in four different soil types supplied or not withsulfamethazine and/or swine manure. After one month of incubation, qPCR analyses and 16S rDNAsequencing were performed to respectively quantify the inoculated strain, its antibiotrophic genesadA, and to characterize the structure of bacterial communities. In parallel, a similar experimentwas carried out with the addition of radiolabeled sulfamethazine, in order to monitoredantibiotrophy activity during incubation by radiorespirometry.Quantitative PCR results showed an effective establishment of the strain and its sulfamethazinedegradinggene (sadA) only under sulfamethazine selection pressure. This reflects the lowcompetitiveness of the strain, which possesses a low invasion potential under non-antibioticcontaminated conditions. Sulfamethazine treated soils differed in their capacity to mineralize theantibiotic. Indeed, in absence of manure and despite the presence of Microbacterium sp. C448, onlyone of the four tested soils exhibited slight mineralization capacities. Whatever the soil type,radiorespirometry analyses showed that manure addition significantly enhanced sulfamethazinemineralization. These results confirm that the presence of functional genes does not necessarilyensure functionality. Moreover, they suggest that sulfamethazine does not necessarily confer aselective advantage to the degrading strain, as a nutritional source. In addition, 16S rDNA sequencinganalyses strongly suggest that sulfamethazine has released trophic niches by biocidal action.Accordingly, manure-originating bacteria and/or Microbacterium sp C448 could have access to lowcompetition or competition-free trophic niches. However, simultaneous inputs of manure and of thestrain could induce detrimental competition for Microbacterium sp. C448, thus forcing it to usesulfamethazine as a nutritional source. Altogether, these results suggest that the studiedantibiotrophic strain can modulate its sulfamethazine-degradation function depending on microbialcompetition and resource accessibility, to establish in an agricultural soil. Most importantly, this workhighlights an increased dispersal potential of antibiotrophs in antibiotic-polluted environments, asantibiotics can not only release existing trophic niches but also constitute new ones.