3.1 HI1A and P1 plasmids transfer to the sewage community
To investigate the transfer dynamics of the HI1A plasmid R27 across the selected sewage communities, we inserted the gfp tag into the Tn10 tetracycline resistance region (supplementary figure 4), resulting in its deletion. Performing conjugation assays, we introduced the donor strain, E. coli MG1655, carrying R27 into sewage communities from three Swedish urban area WWTPs (Ellinge-, Klagshamn-, and Sjölunda-WWTP). In parallel, we performed analogous matings with the IncP1 plasmid, pB10, as a benchmark for broad host range transfer (figure 2a).
We consistently observed plasmid transfer ranging from 2.6 x 10-5 to 2.8 x 10-4 T/R for R27 while the transfer of pB10 ranged from 2.6 x 10-2 to 3.2 x 10-1 T/R in all three sewage communities. This corresponds to an average ~1150-fold lower transfer of R27 than pB10 (p<0.001) (figure 2a).