H-062. Regulation of Vibrio cholerae Biofilm by NspS and MbaA

J. P. Zayner, E. karatan;
Appalachian State Univ., Boone, NC.

Vibrio cholerae, the gram-negative bacterium and the pathogenic agent of the diarrhoeal disease cholera can form biofilms on a variety of biotic and abiotic surfaces. Our research has shown that V. cholerae biofilm formation can be regulated by a pathway involving two proteins, a putative periplasmic polyamine binding protein, NspS, and a GGDEF/EAL family membrane protein, MbaA. NpsS is an activator of biofilm formation; MbaA is a repressor of biofilm formation and a putative c-diGMP phosphodiesterase. Norspermidine, a polyamine, has been shown to increase biofilm formation in an NspS-dependent manner, suggesting that it is the ligand for NspS. We have shown that NspS is able to interact with MbaA and this interaction is amplified with increasing norspermidine concentrations. Alanine replacements of a number of amino acids (D67, D70, D90, D170, W261 and D263) predicted to be in the norspermidine binding site of NspS based on a homology model, lead to a decrease in biofilm formation as well as a decrease of NspS with MbaA interaction. These results suggest that the predicted residues indeed function in norspermidine binding and point to the importance of norspermidine binding in NspS function. From these data we suggest a model in which norspermidine functions as a signal to induce NspS to bind MbaA. We predict that the binding of NspS to MbaA inhibits its putative phosphodiesterase activity, thereby increasing the local or global c-diGMP pools and causing an increase in biofilm formation.