Fig. 1. Induction of putrescine production by mixed microbial cultures.

(A) Extracellular putrescine concentrations in cocultures and individual cultures of 14 bacterial strains in GAM medium supplemented with 2 mM arginine. (B) Extracellular putrescine concentrations in cocultures of each pair of 14 bacterial strains (total 91 combinations). N.D. means not detected; that is, the levels fell below the minimum detectable amount. (C) Extracellular concentration of l-arginine, putrescine, and agmatine in the medium after culture of E. coli for 24 hours (0 to 24 hours), followed by culture of En. faecalis for another 24 hours (24 to 48 hours) in the same medium; E. coli was removed by filtration after 24 hours. (D) Extracellular concentrations of l-arginine, putrescine, and agmatine in the medium after culture of En. faecalis for 24 hours (0 to 24 hours), followed by culture of E. coli for another 24 hours (24 to 48 hours) in the same medium. En. faecalis was removed by filtration after 24 hours.