Résumé
In the context of scarce water resources, the use of treated wastewater (TWW) appears to be a fair and sustainable solution for irrigation of agro-ecosystems. Nevertheless, TWW is known to contain pathogens & pharmaceutical residues including antibiotics and resistant bacteria. To supervise and control this practice but also to assess whether or not TWW participates in the dissemination of antibiotic resistance and identify the resistance mechanisms adopted by bacteria, we have explored the response of the soil microbial communities when exposed to TWW spiked with increasing antibiotic concentrations. The main questions we would like to answer are the followings: Which are the mechanisms and the dynamic of antibiotic resistance in soils? Which are the role of endogenous bacteria (in soil) vs exogenous bacteria (TWW) in antimicrobial resistance dissemination? Which are the fate of antibiotics in soils? Which bacteria are related to these different phenomena? How does the antibiotic concentration play a role on these events?Lab scale microcosms, inoculated with an agricultural soil irrigated with TWW, have been set up and spiked with sulfamethoxazole at environmental concentrations and above (from 0.01 to 1 mg/kg-dry-soil). For 1.5 month, we have monitored key chemical compounds, quantified antibiotics and their transformation products (TPs), the copy number of genes involved in antibiotic degradation, resistance and nitrification/denitrification processes; and determined the bacterial abundance and diversity by qPCR and 16S rRNA sequencing. LC-MS full-scan analysis showed a threshold at 0.5 mg/kg-dry-soil above which the degradation rate of sulfamethoxazole was more important. Different TPs could be detected: desamino & nitro derivatives associated with denitrification processes during the early stages (0-3 days), n-acetyl derivative detected at the highest concentration (1 mg/kg-dry-soil) (0-3 days) and hydroxy-derivative detected up to 28 days. Other TPs are still to be searched and discovered and the data processing using the non-targeted XCMS tool will certainly bring additional information.The on-going multi-analyses will enable us to improve our understanding about the antibiotic resistance mechanisms that really take place in agro-ecosystems and to identify markers (bacterial, TPs or sulfamethoxazole threshold) to monitor in order to better manage the use of TWW.