Polycations which disorganize the outer membrane inhibit conjugation in Escherichia coli.

Outer membrane disorganizing polycation, polymyxin B nonapeptide (PMBN), reduced drastically the production of recombinants when present at sub-MIC concentrations during F'-mediated Escherichia coli conjugation. The decrease of recombinants was accompanied by a less marked decrease of viability in the recipient population in a manner resembling lethal zygosis. No reduction was seen when either donor or recipient was grown in the same PMBN concentration, washed and resuspended to PMBN-free medium before mating. The same concentration of outer membrane disorganizing polycations of higher bactericidal activity (protamine and polylysine) caused only a moderate reduction in transconjugant frequency when present during mating. Spermine and tetralysine, which are not effective disorganizers of the outer membrane, did not reduce the recombinant frequency or the viability of the recipients.