Biodiversity-dependent invasiveness of naive river epilithic biofilms by anthropogenic antibiotic resistance at the interface between the human, animal and environmental spheres

With more than 1 million deaths attributed each year, antibiotic resistance has become a major societal issue. The emergence and dissemination of antibiotic resistance in bacteria rests on two pillars, the enrichment of resistant variants upon selection and the contagion of the resistant bacteria and their resistance genes within and across the human, animal and environmental spheres. Although poorly described, this contagion process necessarily implies the persistence of invading resistant bacteria from one microbiome to another. In this study, we carefully selected a series of headwater streams located in the Vosges Mountains (North-eastern, France), with a clear pristine-like upstream part and well identified primary exposure to modest anthropic activities, to explore invasion processes while avoiding multiple pollution effect. Using high-throughput qPCR for 45 resistance genes and mobile genetic elements we showed that one third of the markers were already widespread, while another third massively invaded the river epilithic biofilm communities at primary exposure to anthropic activities, with the concomitant entry of fecal pollution. We used 16S rRNA gene metabarcoding to explore the structure of the bacterial biofilm communities along river continuums and showed that the extent of the invasion process was inversely correlated with the level of biodiversity, but positively correlated with the magnitude of propagule pressure.