2.6 DNA extractions and sequencing groups
DNA was extracted from 0.25 ml of high biomass samples by the Nucleospin® soil kit (Macherey-Nagel): three samples of the recipient sewage community, filter mated alone; three samples of enriched sewage community/R27; four samples of enriched sewage community/R27; 1 sterile control sample of 0.9 % NaCl solution and 1 sterile control sample of nuclease-free water (Sigma Aldrich). For sample groups with low biomass, DNA was extracted using the GenePurgeDirect™(Nimagen) kit: 4 samples of sewage community/R27 with ~ 10000 transconjugant cells per sample; 4 samples of sewage community/pB10 with ~ 10000 transconjugant cells per sample; 1 sterile control sample of 0.9 % NaCl solution and 1 sterile control sample of nuclease-free water (Sigma Aldrich). For information on sequenced samples see supplementary table 3.