Control
We exctracted DNA from sterile water with prepGEM Bacteria Kit cell lysing kit following manufacturer instructions (New England Biolabs) .  We used 515f-Y (GTGYCAGCMGCCGCGGTAA, Parada 2016), and 806R-B GGACTACNVGGGTWTCTAAT, Apprill 2015) primers to amplify the 16S rRNA gene with illumina adapter overhangs. Samples sequenced on Illumina MiSeq platform using 250 bp x 250 bp paired-end sequencing and aiming at 100,000 reads per sample