16S rDNA Amplicon Sequencing
The V4-V5 regions of the 16S rDNA were amplified using universal primers (515F and 907R). Only sequences between 400-450 bp in length were chosen for further experiments. Sequencing libraries were generated using the TruSeq DNA PCR-Free Sample Preparation Kit (Illumina, USA) following manufacturer's recommendations; index codes were added and then sequenced at Novogene Co., Ltd (Tianjin, China), using an Illumina HiSeq2500 platform with 250 bp paired-end reads generated.