title: 16S amplicon sequences of soil metagenome
design: Microbial genomic DNA was extracted by a freeze-grinding method as described previously (Zhou et al., 1996)  and purified by using DNeasy PowerSoil DNA isolation Kit (QIAGEN; bead tubes were not used). DNA quality was checked by NanoDrop, and double-strand DNA concentration was measured by Quant-iT PicoGreen dsDNA Assay Kit. A two-step PCR was used for library preparation as described previously (Wu et al., 2015). In the first step, the standard primers were used to amplify the V4 region of prokaryotic 16S rRNA genes (515F [5-GTGCCAGCMGCCGCGGTAA-3] and 806R [5-GGACTACHVGGGTWTCTAAT-3]). In the second step, phasing primers were designed and used to increase the base diversity in sequences of sample libraries. The PCR was performed for 11 cycles in the first and 22 cycles in the second step.