Con--mutants: class of mutants in Escherichia coli K-12 lacking a major cell wall protein and defective in conjugation and adsorption of a bacteriophage.

We describe a new class of mutants of Escherichia coli K-12 defective in conjugation (Con(-) mutants). They lack a major protein of the outer membrane and are defective as recipients with Hfr and F' donors and as recipients for several F-like R factors and Col factors. In the case of crosses with an Hfr donor, we have shown that the Con(-) recipient is defective in pair formation. The mutants are resistant to certain phages due to loss of receptor activity.