design: PCR was performed on V4 region of 16S rRNA gene using primers 515F (Parada et al., 2016) and 806R (Apprill et al., 2015). For each sample, triplicate PCR reactions were carried out using high-fidelity polymerase Q5 polymerase (New England Biolabs, Ipswich, USA)The thermal profile consisted of initial denaturation at 98C for 30 sec, followed by 30 cycles of 98 C for 10 sec, 52 C for 30 sec, and 72 C for 30 sec and a final extension step at 72 C for 7 min. Triplicate PCR products were pooled ans sequenced on a Illumina MiSeq with 2x300 cycles and V3 chemistry.