Elevated levels of the norspermidine synthesis enzyme N sp C enhance V ibrio cholerae biofilm formation without affecting intracellular norspermidine concentrations

Biofilm formation in V ibrio cholerae is in part regulated by norspermidine, a polyamine synthesized by the enzyme carboxynorspermidine decarboxylase ( N sp C ). The absence of norspermidine in the cell leads to a marked reduction in V . cholerae biofilm formation by an unknown mechanism. In this work, we show that overexpression of nspC results in large increases in biofilm formation and vps gene expression as well as a significant decrease in motility. Interestingly, increased N sp C levels do not lead to increased concentrations of norspermidine in the cell. Our results show that N sp C levels inversely regulate biofilm and motility and implicate the presence of an effective feedback mechanism maintaining norspermidine homeostasis in V . cholerae . Moreover, we provide evidence that N sp C and the norspermidine sensor protein, NspS , provide independent and distinct inputs into the biofilm regulatory network.