2.4. Microbial DNA Extraction and the 16S rRNA Gene Sequencing
Fecal samples from the participants were collected using a fecal collection kit and delivered on ice bags before and after intervention. Samples were frozen and stored at −20 °C until use. DNA was extracted using a QIAamp Fast DNA Stool Mini Kit (Qiagen, Valencia, CA, USA) according to the manufacturer’s instructions. The purity of the DNA samples was quantified by measuring the A260/280 ratio with the Nanodrop OneC spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA). DNA samples were frozen and stored at −20 °C until use. 110 DNA samples were sent to Novogene Bioinformatics Technology Co., Ltd. (Beijing, China) for paired-end 16S rRNA gene sequencing. The quality and quantity of samples were checked using an Agilent 5400 Bioanalyzer (Agilent, Santa Clara, CA, USA) before library preparation. The V4 region of the 16S rRNA gene was amplified with PCR using 515F (5′-GTGCCAGCMGCCGCGGTAA-3′) and 806R (5′-GGACTACHVGGGTWTCTAAT-3′) primers connected with barcodes [