AlgR is a key transcriptional regulator required for the expression of multiple virulence factors, including type IV pili and alginate in Pseudomonas aeruginosa. However, the regulon and molecular regulatory mechanism of AlgR have yet to be fully elucidated. Here, among 157 loci that were identified by a ChIP-seq assay, we characterized a gene, mucR, which encodes an enzyme that synthesizes the intracellular second messenger cyclic diguanylate (c-di-GMP). A ΔalgR strain produced lesser biofilm than did the wild-type strain, which is consistent with a phenotype controlled by c-di-GMP. AlgR positively regulates mucR via direct binding to its promoter. A ΔalgRΔmucR double mutant produced lesser biofilm than did the single ΔalgR mutant, demonstrating that c-di-GMP is a positive regulator of biofilm formation. AlgR controls the levels of c-di-GMP synthesis via direct regulation of mucR. In addition, the cognate sensor of AlgR, FimS/AlgZ, also plays an important role in P. aeruginosa virulence. Taken together, this study provides new insights into the AlgR regulon and reveals the involvement of c-di-GMP in the mechanism underlying AlgR regulation.
© The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.