Library preparations, sequencing and bioinformatic processing

Library preparations and 16S rRNA sequencing of the V4 region were performed at BGI (Shenzhen, China), on the Illumina MiSeq platform (San Diego, CA, USA). The Quantitative Insights Into Microbial Ecology (QIIME) platform (version 1.8.0) [19], was used for further bioinformatic processing using closed-reference operational taxonomic unit (OTU) mapping to the Greengenes database [20]. Detailed methods are included in the Supplementary Material.