Regulation of VfqI-VfqR Quorum sensing circuit on vgrG operon in VflT6SS orphan cluster of Vibrio fluvialis

  Objective  To explore the regulation of the vgrG operon in the VflT6SS2 orphan clusters by the Quorum sensing system VfqI-VfqR of Vibrio fluvialis.

  Methods  Quantitative reverse transcription PCR was used to detect the relative expression of vgrG mRNA level in wild V. fluvialis strain and VfqI-VfqR system deletion mutant strains. Luminescence of promoter-lux fusion was measured to determine the vgrG promoter activity in wild V. fluvialis strain, derivative mutants and corresponding complemented strains. VfqR-overexpressed plasmid was introduced into Escherichia coli, the luminescence of vgrG promoter-lux fusion was compared to determine the direct effect of VfqR on vgrG operon activation.

  Results  The vgrG mRNA and its promoter activity significantly decreased in the VfqI-VfqR deletion mutants compared with wild V. fluvialis strain. Furthermore, the vgrG promoter activity of ∆vfqR was restored either with trans-complemented plasmid or supplemented with exogenous 3-oxo-C₁₀-HSL, C₁₀-HSL or 3-oxo-C₁₂-HSL AHL molecules. The effects of the three AHLs were similar. However, overexpression of VfqR combined with addition of AHLs had no effect on the promoter activity of vgrG in E. coli.

  Conclusion  The VfqI-VfqR system is one of positive regulators of vgrG operator indirectly tuning the activation of its promoter.