Catalyzes the formation of putrescine from agmatine. agmatine + H2O = putrescine + urea Amine and polyamine biosynthesis; putrescine biosynthesis via agmatine pathway; putrescine from agmatine: step 1/1. Cells show a delay in differentiation to swarmer cells and are unable to migrate effectively on agar surfaces. Putrescine restores normal cell differentiation and migration ability. Belongs to the arginase family. Agmatinase subfamily.