FIG 7.

The size of the VNTR region affects colibactin production via altered clbR transcription. The VNTR region is part of the untranslated 5′ region of the clbR transcript. (A and B) As VNTR regions of various sizes have been observed in different E. coli isolates, we tested the impact of five VNTRs versus 20 VNTRs on clbR promoter activity by the use of λ-attB site-inserted luciferase reporter fusions in E. coli strain M1/5 rpsLK42R grown in M9 medium supplemented with Casamino Acids (A) and in LB (B). Measurements were performed in biological and technical triplicates, and representative graphs are shown. (C and D) We also measured the impact of the size of the VNTR region and of M9 medium (C) or LB (D) on colibactin production of E. coli M1/5 rpsLK42R with altered numbers of VNTRs in the native VNTR site via quantification of the precolibactin cleavage product N-myristoyl-d-asparagine (C14-Asn). The data presented in the graphs were obtained from three biological replicates. *, P < 0.05, unpaired t test.