Metabarcoding of extraction blank
Extraction blank using 300 mL of dH20 following in place of bulk community sample was performed using a modified protocol for the E.Z.N.A Blood Maxi Kit (OMEGA Bio-Tek, Georgia, USA). The V7-V8 region of the nuclear 18S rRNA gene (18S V7-V8) using primers 3F: 5' GYGGTGCATGGCCGTTSKTRGTT 3' and 5' GTGTGYACAAAGGBCAGGGAC 3' (∼325 bp; (Machida and Knowlton 2012) was amplified using polymerase chain reaction (PCR)PCR amplification was conducted in duplicate and products were pooled for library preparation. Pooled amplicons were purified using AMPure® XP beads (Beckman Coulter®), quantified using a Qubit® 1X dsDNA High Sensitivity Fluorescence kit (Thermofisher Scientific). Full methods description is reported at publication in Supplementary file S1.