Bacterial putrescine biosynthesis by arginine and ornithine routes

A reusable bacterial module for putrescine supply through alternative amino-acid routes. In the two-reaction arginine/agmatine route, SpeA decarboxylates L-arginine to agmatine and SpeB hydrolyzes agmatine to putrescine. In the direct ornithine route, SpeC decarboxylates L-ornithine to putrescine. Organisms may encode either or both routes. Upstream amino-acid supply, downstream spermidine synthesis, uptake, and putrescine catabolism are outside the boundary.

The route choice is modeled with variants rather than three optional linear steps: SpeA and SpeB are connected only inside the arginine/agmatine route, while SpeC is an independent alternative. The module is species-neutral; KT2440 proteins are exact exemplars rather than universal members. The lineage-variable AguA plus N-carbamoylputrescine-amidohydrolase route is not modeled here because the commissioned KT2440 review found AguA but no verified completing enzyme. PP_3019 remains an untested candidate, and convergently evolved AguY enzymes mean absence of a canonical AguB does not prove absence of activity. The consolidated OpenScientist module+ppu00330+ PSEPK report and its HTML/PDF artifacts were consumed; no separate gene-level or generic-module report files materialized in this worktree.