OpaR exerts a dynamic control over c-di-GMP homeostasis and cpsA expression in V. parahaemolyticus through its regulation of ScrC and the trigger phosphodiesterase TpdA.

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 pathogen Vibrio parahaemolyticus. The mechanisms by which c-di-GMP levels are dynamically controlled in V. parahaemolyticus are 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 of tpdA by maintaining a baseline level of c-di-GMP. The OpaR-regulated PDEs ScrC, ScrG and VP0117 enable the upregulation of tpdA, 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 on cpsA expression 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 and cpsA expression 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 in V. parahaemolyticus. ImportanceThe 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. We found that OpaR can regulate positively or negatively c-di-GMP accumulation depending on the growth conditions. This dual role has not been reported for orthologues of OpaR, such as HapR from V. cholerae. OpaR controls c-di-GMP homeostasis through PDEs that are absent in V. cholerae, pointing toward further differences in c-di-GMP signaling in these two pathogens. It is important to investigate the origins and consequences of these differences to better understand pathogenic bacterial behavior and its evolution.