title: metagenomics
design: DNA extraction was accomplished by using a DNA extraction kit (Vigen, China), followed by using the bacterial 16S rRNA V3-V4 primers (upstream primer: 5' CCTAYGGGRBGCAAG 3 ', downstream primer: 5' GGACTACNNGGGTATCTAAT 3 ') to amplify the DNA template. PCR amplification was conducted in a total volume of 10 L containing 5 L of 2X Taq PCR Mix (CWbio, China), 0.4 L of each primer, 0.5 L of DNA template and 3.7 L of ddH2O. PCRs were performed under the following conditions: initial denaturation at 94C for 3 min; 30 cycles of 94C for 30 s, 53C for 30 s, and 72C for 30 s; and a final extension at 72C for 3 min. The Vazyme Universal DNA Library Prep Kit for ILLUMINAV2 was used to prepare libraries of the PCR amplification products for next-generation sequencing.