Catalyzes the decarboxylation of carboxynorspermidine and carboxyspermidine. Involved in the regulation of biofilm formation and motility. carboxynorspermidine + H(+) = CO2 + norspermidine carboxyspermidine + H(+) = CO2 + spermidine Homodimer. Overexpression results in large increases in biofilm formation and vpsL exopolysaccharide gene expression as well as in significant decrease in motility. Overexpression does not lead to increased concentrations of norspermidine, putrescine, diaminopropane or spermidine in shaking cell cultures, planktonic cells or biofilm-associated cells of static biofilm cultures. Cadaverine levels are unchanged in shaking cell cultures, but largely increased in planktonic and biofilm-associated cells. Belongs to the Orn/Lys/Arg decarboxylase class-II family. NspC subfamily.