NtrC Adds a New Node to the Complex Regulatory Network of Biofilm Formation and vps Expression in Vibrio cholerae

The biofilm growth mode is important in both the intestinal and environmental phases of the 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 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 expression by RpoN activators. Mutants lacking NtrC had increased biofilm formation and expression. NtrC negatively regulates the expression of core regulators of biofilm formation ( , , and ). NtrC from supported growth and activated expression when nitrogen availability was limited. However, the repressive activity of NtrC toward expression was not affected by the nitrogen sources present. This study unveils the role of NtrC as a regulator of expression and biofilm formation in Biofilms play an important role in the life cycle, contributing to both environmental survival and transmission to a human host. Identifying key regulators of biofilm formation is necessary to fully understand how this important growth mode is modulated in response to various signals encountered in the environment and the host. In this study, we characterized the role of RRs that function as coactivators of RpoN in regulating biofilm formation and identified new components in the biofilm regulatory circuitry.