The second messenger cyclic dimeric guanosine monophosphate (c-di-GMP) plays a central role in controlling decision making processes of vital importance for the environmental survival of the human pathogenVibrio parahaemolyticus. The mechanisms by which c-di-GMP levels are dynamically controlled inV. parahaemolyticusare poorly understood. Here we report our findings regarding the involvement of OpaR in controlling c-di-GMP metabolism in planktonic and surface-attached cells through controlling the expression of the trigger phosphodiesterase (PDE) TpdA and other PDEs such as ScrC. Our results revealed that OpaR negatively modulates the expression oftpdAby maintaining a baseline level of c-di-GMP. The OpaR-regulated PDEs ScrC, ScrG and VP0117 enable the upregulation oftpdA, to a different degree, in the absence of OpaR. We also found that TpdA plays the dominant role in c-di-GMP degradation under planktonic conditions compared to the other OpaR-regulated PDEs. In cells growing over solid media the dominant c-di-GMP degrader role is played by ScrC for 72 hours and passes to TpdA after 96 hours of growth. We also report negative and positive effects of the absence of OpaR oncpsAexpression in cells growing over solid media or forming biofilms over glass, respectively. These results suggest that OpaR can act as a double-edged sword to control c-di-GMP accumulation andcpsAexpression positively or negatively in response to poorly understood environmental factors. Finally, through an in-silico analysis we point out outlets of the OpaR regulatory module that can impact decision making during the motile to sessile transition inV. parahaemolyticus.

The second messenger c-di-GMP is extensively used by bacterial cells to control crucial social adaptations such as biofilm formation. Here, we explore the role of the quorum-sensing regulator OpaR, from the human pathogen V. parahaemolyticus , on the dynamic control of c-di-GMP signaling and biofilm-matrix production.