design: The V3/V4 regions of the 16S rRNA gene were amplified using primers 341F (5-CCTACGGGRSGCAGCAG-3) and 806R (5-GGACTACHVGGGTWTCTAAT-3), with Illumina adapters. The amplification was performed in 35 cycles at 50 C of the annealing temperature. PCR reactions were performed in triplicate for each sample.