Tn library used for infection (group 1)
Genomic DNA was digested with MmeI (New England Biolabs)  for 2.5 h. After 1-h treatment with rAPid alkaline phosphatase (Roche), the genomic DNA was re-extracted using phenol:chloroform:isoamyl alcohol (25:24:1) and precipitated by ethanol. The MmeI-digested fragments were ligated with adapters for Illumina sequencing and amplified with PCR using primers Linker and Tn-index (Tn-index1 ~ Tn-index6 for each sample). After PCR, the amplified fragments of ~120 bp, which contain a 20-bp bacterial genome sequence with transposon junctional region, the adapter sequence, and a unique barcode for distinguishing each sample, were purified by size exclusion