Identification of QS-activating compounds in <i>V. cholerae</i>.

<p>(A) Chemical structures of the eleven QS-activating compounds. The structure of CAI-1 is shown for reference. (B) Differential responses to Class 1 and Class 2 compounds by the <i>V. cholerae</i> Δ<i>cqsA</i> Δ<i>luxS</i> double synthase mutant (BH1578) and the <i>luxO</i>^D47E mutant (BH1651). The normalized light (RLU, relative light units) produced was monitored in the absence (white) and presence of Class 1 (gray) or Class 2 (black) compounds. A representative experiment is shown using compound 1 (Class 1) and compound 11 (Class 2) from (A). (C) QS dose-response curves of <i>V. cholerae</i>. The normalized light (RLU, relative light units) produced by the <i>V. cholerae</i> Δ<i>cqsA</i> Δ<i>luxS</i> mutant carrying the <i>lux</i> operon (BH1578) is plotted as a function of the concentration of the eleven QS-activating compounds shown in (A). Black curves denote responses to Class 1 compounds. Blue curves denote responses to Class 2 compounds. The red curve denotes the response to the native autoinducer CAI-1, which is the positive control. Error bars are present, but are too small to be observed in the plot. The bars represent standard errors of the mean for three independent trials. (D) Effect of compound 11 on expression of <i>qrr</i>4. Expression of <i>qrr</i>4 was monitored in a <i>V. cholerae luxO</i>^D47E strain carrying a <i>qrr</i>4-<i>gfp</i> transcriptional reporter (SLS353). The response is shown in the presence and absence of 50 µM compound 11. Expression of <i>qrr</i>4-<i>gfp</i> from the Δ<i>luxO</i> mutant (SLS373) is shown for reference. AU denotes arbitrary units. Error bars represent standard errors of the mean for three independent trials.