Cathode solution_16S amplicon NGS
Solution samples (~ 40 mL) were pelleted at 13000 rpm for 20 min. From each pellet and biofilm, DNA was extracted using the DNeasy PowerSoil Kit (Qiagen, Germany) accord-ing to manufacturers instructions after an initial thermal treatment (5 cycles of 10 min at -20C and 10 min at 65C). DNA yield and purity was quantified on a Nanodrop 1000 spec-trophotometer (Thermo Fisher Scientific) while quality was determined through gel elec-trophoresis 1% (w/v) 1TAE agarose gels. DNA was stored at -80C until analyses.  The NGS was performed at Novogene Co. Ltd (Cambridge, UK). Sequencing targeted the V3 and V4 regions of the bacterial 16S rRNA gene using primers 341F (CCTAYGGGRBG-CASCAG) and 806R (GGACTACNNGGGTATCTAAT) (Youngseob et al., 2005). The gen-erated DNA libraries were sequenced with an Illumina NovaSeq PE264