Anionic sites on the envelope of Salmonella typhimurium mapped with cationized ferritin.

Binding of either ferritin (F) or cationized ferritin (CF) was employed to indicate the surface charge of the envelope of mainly two Salmonella typhimurium strains (395 MR10, a Rd-mutant, and LT2-M1, a UDP-galactose-4-epimerase-less mutant). Lowering the pH from 7 to 4 decreased binding of CF, but increased binding of F. At low concentrations, the distribution of CF on S. typhimurium 395 MR10 was in general random, with individual ferritin molecules often forming clusters of two or three particles. At ionic strengths of 0.25M NaCl, ferritin produced distinctive, larger clusters at relatively few sites (10-50/cell). Addition of galactose to cultures of growing S. typhimurium, LT2-M1 reduced the binding of CF in 1-10 min, and numerous ferritin-free areas became visible. Possibly this is caused by a pluri-focal reduction in the negative cell surface charge that was generated at the multiple sites of export of new, smooth-type lipopolysaccharide, which either exhibits lesser charge or masks a preexisting surface charge. Dividing cells may show unequal charges on the prospective daughter cells, and the difference in the capacity for ferritin adsorption of both daughter cells is sharply separated at the division site.