NtrC adds a new node to the complex regulatory network of biofilm formation and vps expression in Vibrio cholerae

Abstract

The biofilm growth mode is important in both the intestinal and environmental phases of the Vibrio cholerae life cycle. Regulation of biofilm formation involves several transcriptional regulators and alternative sigma factors. One such factor is the alternative sigma factor RpoN, which positively regulates biofilm formation. RpoN requires bacterial enhancer-binding proteins (bEBPs) to initiate transcription. The V. cholerae genome encodes seven bEBPs (LuxO, VC1522, VC1926 [DctD-1], FlrC, NtrC, VCA0142 [DctD-2], and PgtA) that belong to the NtrC family of response regulators (RRs) of two-component regulatory systems. The contribution of these regulators to biofilm formation is not well understood. In this study, we analyzed biofilm formation and the regulation of vpsL expression by RpoN activators. Mutants lacking NtrC had increased biofilm formation and vpsL expression. NtrC negatively regulates the expression of core regulators of biofilm formation (vpsR, vpsT, and hapR). NtrC from V. cholerae supported growth and activated glnA expression when nitrogen availability was limited. However, the repressive activity of NtrC toward vpsL expression was not affected by the nitrogen sources present. This study unveils the role of NtrC as a regulator of vps expression and biofilm formation in V. cholerae.