Abstract
This paper describes the isolation of mutants resistant to colicins of group B (i.e., colicins B, D, G, H, Ia, Ib, M, Q, S1, and V). The 145 mutants studied in detail can be divided into nine phentopyic classes, based on their colicin-resistance patterns. They include the previously isolated tonA, tonB exbB and cir mutants. Each of the different phenotypic classes of mutants has been partially characterized, and some approximately mapped. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis has revealed substantial changes in the composition of the outer membrane proteins of exbB and tonB mutants.