A spermidine retroconversion activity in A. tumefaciens. Polyamine content assessed by HPLC in the ΔODC strain after growth in CDM containing either (A) putrescine (Put) or (B) spermidine (Spd) at the indicated concentrations. After the second subculture (30°C), cell numbers were adjusted through OD600 nm equalization and, after centrifugation of equal cell number aliquots, the cell pellet was washed three times with PBS. Orn, ornithine; Fl, AccQ-Fluor tag; IS, internal standard (1,7-diaminoheptane).