2.4. DNA extraction and PCR amplification
Microbial DNA was extracted from grass carp intestine samples
by using the Bacterial DNA Kit (50) (Omega, USA) following manufacturer's
instruction. For each sample, DNA was extracted in triplicate
to avoid bias, and the extracts from the same sample were
pooled [30]. Purity of DNA extractedwas verified by electrophoresis
on ethidium bromide staining 1% agarose gels, and concentration
was analyzed spectrophotometrically using the M200pro (TECAN,
Switzerland). The extracted DNAwas stored at 80 C until use. The
V4eV5 region of the bacteria 16S ribosomal RNA gene were
amplified by PCR (95 C for 2 min, followed by 25 cycles at 95 C for
30 s, 55 C for 30 s, and 72 C for 30 s and a final extension at 72 C
for 5 min). The primers used were 515F 50-barcode-
GTGCCAGCMGCCGCGG-30 and 907R 50-CCGTCAATTCMTTTRAGTTT-
30 , where barcode is an eight-base sequence unique to each sample.
PCR reactions were performed in triplicate 20 mL mixture containing
4 mLof5FastPfu Buffer, 2 mL of 2.5mMdNTPs, 0.8 mL of each primer
(5 mM), 0.4 mL of FastPfu Polymerase, and 10 ng of template DNA.