Biosynthesis of putrescine and spermidine in Pseudomonas aeruginosa. AguA, agmatine deiminase; AguB, N-carbamoylputrescine aminotransferase; SpeA, arginine decarboxylase; SpeC, ornithine decarboxylase; SpeD, SAM decarboxylase; SpeE, spermidine synthase; SpuDEFGH, spermidine ABC transporter substrate-binding protein; PotABCD, polyamine ABC transporter substrate-binding protein; SAM, S-adenosyl methionine; dSAM, decarboxylated SAM.