The purified amplicons were prepared for Illumina sequencing by constructing a library using the TruSeq® DNA PCR-Free Sample Preparation Kit (Illumina, USA) following the manufacturer’s recommendations. The final library concentrations and quality were checked using a Qubit@ 2.0 Fluorometer (Thermo Scientific) and an Agilent Bioanalyzer 2100 system, respectively. Lastly, the library was sequenced on a Hiseq2500 PE250 platform at the Novogene Bioinformatics Technology Co., Ltd. (Beijing, China), and 250 bp paired-end reads were generated.