design: Amplification was performed with primers for the V3-V4 region of the 16S rRNA gene, 341F (CCTACGGGRSGCAGCAG, doi: 10.1371/journal.pone.0007401) and 806R (GGACTACHVGGGTWTCTAAT, doi: 10.1038/ismej.2012.8). The libraries were sequenced using the MiSeq Sequencing System equipment (Illumina Inc., USA).