19The supply of clean water for human consumption is being challenged by the appearance 20 of pesticide pollutants in groundwater ecosystems. Biological rapid sand filtration is a 21 commonly employed method for the removal of organic and inorganic impurities in water 22 32 RSF1010, pKJK5 and TOL (pWWO), using a dual-fluorescent bioreporter platform 33 combined with FACS and 16S rRNA gene amplicon sequencing. Our results reveal that 34 plasmids can transfer at high frequencies and across distantly related taxa from rapid 35 sand filter communities, emphasizing their suitability for introducing pesticide degrading 36 determinants in the microbiomes of underperforming water purification plants. 37 38 65 129 meta-parental mating setup described previously (Klümper et al., 2015). Following this 130 approach, plasmids are tracked through a inserted gfp marker controlled by a lacIq 131 repressible promoter. The donor strain additionally harbors a chromosomal lacIq-Plpp-132