2.6. Fecal 16S rRNA Gene Sequencing

The QiaAmp DNA Stool Mini Kit (Qiagen, Valencia, CA, USA) was used to extract genomic DNA from the collected fecal pellets. Sequencing libraries of the 16S V3-4 region were prepared according to the Illumina 16S Metagenomic Sequencing Library Preparation Guide [16,18,32,38], and 16S rRNA gene sequencing was performed exactly as described previously [16,18,32,38].