Repression by H- NS of genes required for the biosynthesis of the V ibrio cholerae biofilm matrix is modulated by the second messenger cyclic diguanylic acid.

Expression of V ibrio 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. [ABSTRACT FROM AUTHOR]