Biofilm samples were taken with a sterile cannula directly from the electrode (n = 2 for each reactor). Genomic DNA was extracted with the NuceloSpin Tissue Kit (Macherey-Nagel, Germany). The microbial community composition on DNA level was analysed with a standard TRFLP procedure using the primers UniBac27f (FAM labelled) and Univ1492r for amplifying the partial sequence of the 16S rRNA gene of bacteria [54 ].
The PCR Master Mix contained 6.25 μL enzyme mix (MyTaq HS Red Mix, 2x,Bioline, Germany), 0.25 μL of each primer (5 ρmol μL−1, MWG Biotech, Germany), 4.75 μL nuclease-free water, and 1 μL genomic DNA (about 360–720 ng). The PCR cycle parameters were as follows: 1 min at 95°C, 25 cycles of 15 s at 95°C, 15 s at 54°C, and 2 min at 72°C, followed by a 10 min final extension step at 72°C [55 (link)]. PCR products were purified (Sure Clean Plus, Bioline) and digested with restriction endonucleases HaeIII and RsaI (New England Biolabs GmbH, Germany). After product precipitation (EDTA/EtOH), TRFLP analysis was performed using an ABI PRISM Genetic Analyzer 3130xl (Applied Biosystems, USA) and MapMarker® 1000 (BioVentures Inc., USA) as size standard.
The PCR Master Mix contained 6.25 μL enzyme mix (MyTaq HS Red Mix, 2x,Bioline, Germany), 0.25 μL of each primer (5 ρmol μL−1, MWG Biotech, Germany), 4.75 μL nuclease-free water, and 1 μL genomic DNA (about 360–720 ng). The PCR cycle parameters were as follows: 1 min at 95°C, 25 cycles of 15 s at 95°C, 15 s at 54°C, and 2 min at 72°C, followed by a 10 min final extension step at 72°C [55 (link)]. PCR products were purified (Sure Clean Plus, Bioline) and digested with restriction endonucleases HaeIII and RsaI (New England Biolabs GmbH, Germany). After product precipitation (EDTA/EtOH), TRFLP analysis was performed using an ABI PRISM Genetic Analyzer 3130xl (Applied Biosystems, USA) and MapMarker® 1000 (BioVentures Inc., USA) as size standard.