Fig. 4

Yield detection of butenyl-spinosyn and expression levels analysis of polyketide synthase genes. a HPLC detection of the production of butenyl-spinosyn in the wild-type and the mutant strains. b Morphological differences of the surviving insects. c The difference in insecticidal toxicity of the fermentation broth supernatant between the wild-type and mutant strains. d qRT-PCR analysis of the expression levels of polyketide synthase genes in the wild-type and mutant strains. The transcriptional levels of these genes (busA, busB, busC, busD, busE) in ::bfr were 2.40-, 1.69-, 3.05-, 2.33-, and 2.55-fold higher than those in the wild-type, respectively. The transcriptional levels of them in Δbfr were 0.43, 0.60, 0.49, 0.53, and 0.64 times that of the wild-type, respectively. 16S rRNA served as the normalization control. Averages from three biological replicates are shown. Error bars represent the standard deviation of the mean. *, **and *** indicate P < 0.05, P < 0.01 and P < 0.005, respectively, compared to the wild-type under the same conditions