sequences of bacteria
The extracted DNA was amplifed using the universal primer set 338F (5-ACTCCTACGGGAGG CAGCAG-3) and 806R (5-GGACTACHVGGGTWTCTAAT-3), which targeted the V3-V4 region of the bacterial 16S ribosomal RNA (rRNA) genes. For all reactions, a 25-L system with 25ng DNA template, 12.5 L PCR premix, and 2.5 L forward primer and reverse primer were used and fnally adjusted to 25 L with ddH2O. The PCR amplifcation conditions were as follows: pre-denaturation (95C, 3min), 30 cycles of amplifcation (95C denaturation for 30s, 60C annealing for 30s, 72C extension for 45s), and fnal extension at 72C for 10min. The PCR products were examined on a 1.5% agarose gel and purifed using a QIAGEN Gel Extraction Kit (Qiagen, Dusseldorf, Germany).