Fig 3. Intracellular concentrations of polyamines determined.

A,B: Concentrations of putrescine (A), spermidine (B) and spermine were assessed by HPLC in exponentially growing wild-type S Typhimurium strain 14028s or the isogenic speE oat mutant (AAD58) in N-minimal medium with the indicated Mg²⁺ concentrations. Stars denote statistical significance compared to wild-type in 800 μM Mg²⁺. ***: p<0.001; *: p<0.05; ns: not significant (Student’s t-test, n = 3). C,D: Same as above but for wild-type E. coli strain MG1655. None of the tested polyamines was detectable in the speB speC speF mutant (AAD95). Spermine was not detected under the investigated conditions (detection limit = 0.2 mM).