Control of salmonellosis pacifarin biosynthesis by iron.

Enterobacter cloacae strain SS4-56 produced salmonellosis pacifarins when grown in an iron-depleted synthetic medium to which 3.16 X 10-7 g-atom of iron had been added per liter, but did not do so when grown in iron-depleted medium supplemented with 3.16 X 10-4 g-atom of iron per liter. The addition of 3.16 X 10-4 g-atom of ferric iron per liter to a pacifarin-containing culture supernatant fluid had no significant effect upon the ability of the active pacifarins present, when administered per os, to protect mice from an otherwise fatal infection produced by a sequential injection of avirulent and virulent strains of Salmonella typhimurium.