2.7 qRT-PCR
The genes correlated with biosynthesis of surfactin, includingsrfA , sfp , spx and perR were analyzed by qRT-PCR. Single colony of each strain was selected for inoculating LB medium and cultured at 37 oC overnight, then the broth was transferred into fresh LB medium, or LB medium added with glucose (10 g/L) or H2O2 (2.0 mM) at a ratio of 1% (v/v). After incubation at 37 oC for 24 h, the broth was collected for isolating mRNA with RNeasy Mini Kit (Qiagen, German). cDNA was produced by reverse transcription with 1 µg RNA, iScript Select cDNA Synthesis Kit and random oligonucleotide primers. qRT-PCR was performed with cDNA, SsoAdvanced Universal SYBR Green Supermix (Bio-Rad) and target-specific primers in Table S4 (Supplementary materials) in CF96 Real-Time System (Bio-Rad) as following: 1 cycle of 95 oC for 5 min, 40 cycles of 95oC for 10 s, 45 oC for 20 s and 70oC for 30 s. All expression data were normalized to the copy number of 16S rRNA in each sample [38].