design: V4 region of the bacterial 16S rRNA gene was amplified with the conserved primers 515F (5_-GTGYCAGCMGCCGCGGTAA-3_) and 806R (5_-GGACTACNVGGGTWTCTAAT-3_). Bacterial amplicon sequencing was performed on Illumina Miseq with Miseq reagent kit V2.