16S rRNA gene amplification, sequencing and analysis
The V3 ~ V4 hypervariable regions of the 16S rRNA gene were amplified using specific primers (338F: 5ʹ-ACTCCTACGGGAGGCAGCAG-3ʹ; 806R: 5ʹ-GGACTACHVGGGTWTCTAAT-3ʹ) with barcodes, and all PCRs were performed with PhusionUPARSE software (Uparse v7.0.1001, 