FIG 6.

Exogenous alginate downregulates PQS quorum sensing. (A) The PQS quorum sensing regulon. PQS synthesis is dependent on the pqsABCD genes located in the pqs operon. Both HHQ and HQNO have direct antimicrobial properties, while PQS is the ligand for PqsR/MvfR. When the PQS level is high, this ligand interacts with PqsR/MvfR to positively regulate many downstream virulence factors. PQS has a direct iron-chelating function and promotes the expression of siderophore-encoding genes. The downstream effects listed here focus on effects relevant to this study and are not exhaustive. (B to F) LC-MS/MS was used to quantify HQNO (B), HHQ (C), PQS (D), PCA (E), and pyocyanin (F) produced by P. aeruginosa. Panel B includes the key for all graphs in this figure. Significance was determined for each experiment by one-way ANOVA with Dunnett’s posttest comparison to P. aeruginosa PAO1. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.