2.2 | DNA extraction and sequencing
Fecal DNA extraction was performed using the QIAamp DNA Stool Mini Kit (Qiagen, Valencia, CA, USA) according to the standard protocol. The quality and concentration of the DNA were determined using a Nanodrop (ND-1000) spectrophotometer (Nanodrop Technologies, Wilmington, DE, USA), and the integrity was confirmed by agarose gel electrophoresis. DNA samples were stored at -20°C until use. Shotgun sequencing was performed using an Illumina NovaSeq 6000, with at least 10 Gb per sample.