ANTIBIOTIC RESISTANCE GENE DYNAMICS ALONG A WASTEWATER EFFLUENT, SOIL, CROP CONTINUUM: IS SOIL A BARRIER TO DISSEMINATION?

Roberto B.M Marano 1,2 Joao Gatica 1,2 Vijay Tripathi 2 Eddie Cytryn 2 Edouard Jurkevitch 1
1The Robert H. Smith Faculty of Agriculture, Food and Environment, Hebrew University, Rehovot, Israel
2Institute of Soil, Water and Environmental Sciences, The Volcani Center, Agriculture Research Organization, Rishon Lezion, Israel

Wastewater treatment plants consolidate high loads of fecal and environmental bacteria and residual concentrations of antibiotics; and consequentially, effluents released from these facilities may contribute to antibiotic resistance in downstream ecosystems. This is especially relevant in arid environments, where treated wastewater (TWW) is often used for irrigation. The goal of this study was to assess the impact of TWW irrigation on dissemination of antibiotic resistance in terrestrial and food-associated microbiomes. The diversity and abundance of ARGs was evaluated in freshwater and TWW, as well as in freshwater- and TWW-irrigated soils and crops using a novel high-throughput amplicon sequencing methodology that specifically targeted ARGs associated with integron gene cassettes; and through quantitative PCR that assessed the abundance of selected ARGs along freshwater- and TWW-irrigated, water-soil-crop continuum. In tandem we applied comparative in-silico-based analyses of human gut, wastewater and soil metagenomes to determine specific associations between wastewater and soil resistomes. Our results revealed that wastewater effluents contain a diverse array of ARGs, and that specific ARGs and class 1 integrons are profuse and strongly associated with wastewater effluents. Frequently, class 1 integron abundance was positively correlated with treated wastewater irrigation. In contrast, wastewater-associated ARGs were generally below quantifiable levels in both irrigated soils and crops and there was no correlation between ARG levels in irrigation water and those detected in soil, suggesting marginal survival of effluent-derived bacteria in the soil and nominal horizontal transfer of these ARGs to soil and produce microbiomes. Collectively, the study indicates that the distribution of ARGs in the environment is highly complex and is associated with phylogenetic constraints as well as natural and anthropogenic factors.









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