Characterizing The Domains Of The Biofilm Regulator MbaA In Vibrio Cholerae

Vibrio cholerae is a pathogen that is believed to survive within its environment in a biofilm state but can only cause infection in a planktonic state. Polyamines modulate biofilm formation and are sensed by the periplasmic protein NspS. NspS is then hypothesized to bind to the periplasmic region of MbaA: a membrane protein that has C-terminal GGDEF and EAL domains. GGDEF and EAL domains are associated with diguanylate cyclase and phosphodiesterase activity, respectively. Diguanylate cyclases produce the secondary messenger c-di-GMP while phosphodiesterases break down c-di-GMP. Increasing c-di-GMP enhances biofilm formation. MbaA is a phosphodiesterase; this study was to determine the function of the GGDEF domain. Individual domains were purified and the reaction products identified using HPLC. The EAL domain was independently functional and the GGDEF domain has no apparent activity in vitro. EAL and GGDEF domain deletions have similar phenotypes to the mbaA background. This indicates that both domains are necessary for phosphodiesterase function in vivo. The domains were then deleted within an overexpression plasmid pMbaA. MbaAGGDEF decreased biofilm formation similar to that of the biofilm formation of pMbaA. pMbaAEAL increased biofilm formation similar to that of a mbaA mutant. Indicating the GGDEF domain is not necessary for phosphodiesterase activity.