design: 16S DNA libraries were prepared according to Illumina workflow http://support.illumina.com/documents/documentation/chemistry_documentation/16s/16s-metagenomic-library-prep-guide-15044223-b.pdf with primers targeting the V3 and V4 regions of the SSU ribosomal RNA (rRNA) gene such as forward S-D-Bact-0341-b-S-17 and reverse S-D-Bact-0785-a-A-21 [Klindworth et al., 2013]. The libraries were sequenced in MiSeq (Illumina) using 2  300 bp paired-end MiSeq v3 reagent kit.