Mobilization of Escherichia coli R1 silver-resistance plasmid pJT1 by Tn5-Mob into Escherichia coli C600.

Escherichia coli R1 is an Ag(+)-resistant strain that, as we have shown recently, harbours at least two large plasmids, pJT1 (83 kb) and pJT2 (77 kb). Tn5-Mob was introduced into the E. coli R1 host replicon via conjugation on membrane filters. The transfer functions of plasmid RP4-4 were provided in this process and Tn5-Mob clones mated with E. coli C600 yielded Ag(+)-resistant transconjugants. This mobilization procedure allowed transfer and expression of pJT1 Ag+ resistance in E. coli C600. Prior to use of Tn5-Mob mobilization, it was not possible to transfer Ag(+)-resistant determinant(s) into E. coli by conjugation or transformation including high-voltage electroporation. E. coli C600 containing PJT1 and PJT2 displayed decreased accumulation of Ag+ similar to E. coli R1.E. coli C600 could not tolerate 0.1 and 0.5 mM Ag+, rapidly accumulated Ag+ and became non-viable. Tn5-Mob mobilization may be useful in the study of metal resistance in bacteria, especially in strains not studied for resistance mechanisms.