Repression by H‐NS of genes required for the biosynthesis of the Vibrio cholerae biofilm matrix is modulated by the second messenger cyclic diguanylic acid

• Published in: Molecular microbiology 2015-08, Vol.97 (4), p.630-645
• Main Authors: Ayala, Julio C., Wang, Hongxia, Silva, Anisia J., Benitez, Jorge A.
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biofilms; Biofilms - growth & development; Biosynthesis; Chromatin; Cyclic GMP - analogs & derivatives; Cyclic GMP - metabolism; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Extracellular Matrix - metabolism; Gene Expression Regulation, Bacterial; Genes; Gram-negative bacteria; Protein Binding; Protein Biosynthesis; Proteins; Second Messenger Systems; Vibrio cholerae - genetics; Vibrio cholerae - metabolism; Vibrio cholerae - physiology
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.13058

Summary Expression of Vibrio cholerae genes required for the biosynthesis of exopolysacchide (vps) and protein (rbm) components of the biofilm matrix is enhanced by cyclic diguanylate (c‐di‐GMP). In a previous study, we reported that the histone‐like nucleoid structuring (H‐NS) protein represses the transcription of vpsA, vpsL and vpsT. Here we demonstrate that the regulator VpsT can disrupt repressive H‐NS nucleoprotein complexes at the vpsA and vpsL promoters in the presence of c‐di‐GMP, while H‐NS could disrupt the VpsT‐promoter complexes in the absence of c‐di‐GMP. Chromatin immunoprecipitation‐Seq showed a remarkable trend for H‐NS to cluster at loci involved in biofilm development such as the rbmABCDEF genes. We show that the antagonistic relationship between VpsT and H‐NS regulates the expression of the rbmABCDEF cluster. Epistasis analysis demonstrated that VpsT functions as an antirepressor at the rbmA/F, vpsU and vpsA/L promoters. Deletion of vpsT increased H‐NS occupancy at these promoters while increasing the c‐di‐GMP pool had the opposite effect and included the vpsT promoter. The negative effect of c‐di‐GMP on H‐NS occupancy at the vpsT promoter required the regulator VpsR. These results demonstrate that c‐di‐GMP activates the transcription of genes required for the biosynthesis of the biofilm matrix by triggering a coordinated VpsR‐ and VpsT‐dependent H‐NS antirepression cascade. This article shows how changes in the bacterial intracellular cyclic diguanylate (c‐di‐GMP) pool reversibly control the expression of vps and rbm genes required to make the biofilm extracellular matrix. The nucleoid associated protein H‐NS binds to the promoters of these genes to silence their expression when the c‐di‐GMP concentration is low. When the c‐di‐GMP pool is elevated, its receptors VpsR and VpsT sequentially displace H‐NS from promoters to turn on gene expression.