Bypass of receptor-mediated resistance to colicin E3 in Escherichia coli K-12

Colicin E3 was found to kill, under conditions of osmotic shock, cells lacking a functional outer membrane receptor (bfe). Under such conditions, component A of the colicin, carrying endonucleolytic activity, also killed bfe cells, whereas fragment T2, obtained by tryptic digestion of the colicin and also active endonucleolytically, was inactive. Tolerance to the colicin caused by defects in the outer membrane could be overcome by osmotic shock, whereas tolerance probably caused by an altered plasma membrane could not.