Fig. 5

Effect of tryptophol acetate on the expression of genes associated with quorum sensing in V. cholerae. a Relative gene expression in V. cholerae VC1 WT assessed by RT-qPCR. The blue bars correspond to bacteria untreated with tryptophol acetate, while the grey bars indicate gene expression levels recorded following addition of the compound. The relative magnitude of gene levels was defined as the copy number of cDNA of genes in the QS pathway normalized in relation to the expression of a reference housekeeping gene not affected by the treatment. Error bars indicate standard deviations of four independent cultures. *p < 0.002, **p < 0.0001, ***p < 0.05 versus the untreated bacteria calculated by ANOVA followed by Tukey’s post hoc analysis. b Scheme depicting the effects of tryptophol acetate upon QS gene regulation of biofilm formation and virulence of V. cholerae in high cell density conditions (as recorded in the RT-qPCR experiments). The solid black arrows indicate transcription activation, the grey arrows indicate inactivation, while the dashed lines account for transcription repression induced by tryptophol acetate. Genes shown in grey background with red borders—hapR and ctxA—were downregulated by tryptophol acetate, while blue backgrounds account for genes that were upregulated due to repression of hapR (mimicking low cell density conditions), see text