Involved in norspermidine biosynthesis. Catalyzes the synthesis of carboxynorspermidine from L-aspartate 4-semialdehyde and 1,3-diaminopropane. Is also active with putrescine as a substrate. Essential for biofilm formation. carboxynorspermidine + H2O + NADP(+) = H(+) + L-aspartate 4-semialdehyde + NADPH + propane-1,3-diamine carboxyspermidine + H2O + NADP(+) = H(+) + L-aspartate 4-semialdehyde + NADPH + putrescine Deletion of the gene abolishes norspermidine and spermidine biosynthesis, and results in increased accumulation of diaminopropane. Deletion leads to a reduction in growth rate of planktonic cells and severely reduced biofilm formation. Belongs to the saccharopine dehydrogenase family. carboxynorspermidine synthase subfamily.