library_construction_protocol: V3 and V4 regions of 16S rRNA were amplified by PCR with primers of 341F:5'-CCTA CGGG NGGC WGCA G-3' and 805R: 5'-GACT ACHV GGGT ATCT AATC C-3'. The amplified DNA was then processed for gene sequencing with Illumina MiSeq-PE250 system. QIIME2 was adopted to analyze the gene sequences and classify the operational taxonomic units (OTUs) on the basis of 97% sequence identity.