ADAPTIVE MUTATION IN ESCHERICHIA-COLI - A ROLE FOR CONJUGATION

When subjected to selective conditions that impose starvation, a bacte rial population can accumulate mutations, called adaptive, that allow colony formation. Here, the reversion of a lac allele under selective conditions, in a model system using Escherichia coli with the lac muta tion on an F' plasmid, was shown to require the conjugational capacity of the plasmid. Reversion associated with transfer was shown, and whe n the same lac allele was chromosomal, reversion to Lac(+) was 25 to 5 0 times less frequent. Postplating reversion was 25 times less when ma ting was inhibited by the presence of detergent. Mutability associated with conjugation provides new ways of thinking about the origin of ad aptive mutations.