Fecal sample collection and DNA extraction
We followed the standard protocols of fecal sample collection and processing [Samples were sent in cold-chain with dry ice to Novogene Co., Led. (Beijing, China) for subsequent procedures. Genomic DNA was extracted from feces using the QIAamp Fast DNA Stool Mini Kit (Qiagen, Hilden, Germany) according to the manufacturer’s instructions. After the evaluation of genomic DNA concentration and quality, DNA samples, greater than 1 µg and with an OD value between 1.8 ~ 2.0, were qualified for further analysis.