Response of spheroplasts and chelator-permeabilized cells of gram-negative bacteria to the action of the bacteriocins pediocin SJ-1 and nisin.

We have attempted to bypass the outer membrane (OM) barrier of Escherichia coli and Salmonella typhimurium with pediocin SJ-1 (as compared with nisin) using chelating agents as OM permeabilizers. EDTA, and to less extent EGTA, enabled nisin, but not pediocin SJ-1, to permeate the cell OM of E. coli, to have access to the cytoplasmic membrane and to cause subsequent permeability changes, indicated by an increase in ANS fluorescence intensity and a shift of its emission maximum. Such spectral changes did not occur when, prior to addition, EDTA was saturated with Ca2+ and Mg2+. ANS fluorescence data indicated that, in spite of the fact that pediocin SJ-1 did traverse the EDTA-permeabilized OM of E. coli, it did not cause perturbation of its cytoplasmic membrane and was, therefore, unable to cause cell death. Spheroplasts prepared from E. coli were lysed when treated with nisin but not with pediocin SJ-1. We suggest that the resistance of Gram-negative bacteria to pediocin SJ-1 is due not only to this material's inability to permeate the OM but also (in contrast to nisin) to its inability to interact with the cytoplasmic membrane.