design: Filtering of water samples and extraction of DNA using the standard protocol for Dneasy PowerWater Kit (Qiagen, Germany). Duplicate amplification of the 16S rRNA gene region 18 (bV18A): [8F] AGRGTTYGATYMTGGCTCAGand [1391R] GACGGGCGGTGWGTRCA. Initial denaturation at 98 C for 3 min, 25 cycles of amplification (98 C for 30 s, 62 C for 20 s,72 C for 2 min) and a final elongation at 72 C for 5 min. Sequencing was performed using a MinION R10.4.1 flowcell (Oxford Nanopore Technologies, UK)