Penetration of colicin M into cells of Escherichia coli.

A new class of colicin M-tolerant mutants of Escherichia coli K-12 was isolated. The mutants exhibited an unusually high tolerance in that they were unaffected by colicin titers of 10(6). The tolerance was confined to colicin M. It was mapped at a locus called tolM, which is close to rpsL. The following gene order was determined: aroE, tolM, rpsL, cysG. The tolerance could be caused by a defect in the uptake of colicin M or by a mutation at the site of action. Insensitive tonA and tonB mutants became sensitive to colicin M upon treatment by osmotic shock, whereas the tolM mutants remained insensitive. Trypsin rescue experiments showed that the tonB-dependent uptake of colicin M required energy like the other tonB-related transport processes. When bound to energy-depleted cells, colicin M prevented adsorption of phage T5. The receptor became accessible to the phage when the cells were energized, except in tonB mutants. These data suggest that the function controlled by the tonB gene is required for the translocation of colicin M from its initial binding site at the tonA-coded receptor protein to the target.