Cyclic diguanylate regulates Vibrio cholerae virulence gene expression

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• Cyclic diguanylate (c-diGMP) is a crucial bacterial second messenger.
• In Vibrio cholerae, c-diGMP regulates cell surface properties, including biofilm formation.
• The VieSAB system and its regulator VieA are involved in c-diGMP metabolism.

Purpose of the Study:

• To investigate the role of VieA's c-diGMP phosphodiesterase activity in cholera toxin (CT) production.
• To elucidate the regulatory mechanisms of c-diGMP in V. cholerae virulence and biofilm formation.
• To determine the impact of c-diGMP levels on V. cholerae pathogenesis in a host model.

Main Methods:

• Analysis of ctxAB and toxT transcription under varying c-diGMP conditions.
• Ectopic expression of diguanylate cyclase and phosphodiesterase enzymes.
• Site-directed mutagenesis of VieA to alter c-diGMP levels.
• Assessment of V. cholerae virulence in an infant mouse model.

Main Results:

• VieA's c-diGMP phosphodiesterase activity is essential for enhancing CT production at the transcriptional level.
• Altering intracellular c-diGMP concentrations directly impacts ctxAB transcription.
• VieA activity is required for maximal toxT transcription, independent of ToxR or TcpP.
• A mutation in VieA leading to increased c-diGMP resulted in V. cholerae attenuation in mice.

Conclusions:

• c-diGMP signaling plays a dual role in V. cholerae, repressing virulence genes (ctxA, toxT) at high concentrations and activating biofilm genes.
• VieA's phosphodiesterase activity is critical for promoting virulence by lowering c-diGMP levels.
• c-diGMP signaling is vital for V. cholerae's adaptation and transition from environmental survival to host colonization.