Isolation and characterization of catabolite repression-resistant mutants of Escherichia coli

A method has been developed for the isolation of Escherichia coli mutants which are resistant to catabolic repression. The method is based on the fact that a mixture of glucose and gluconate inhibits the development of chemotactic motility in the wild type, but not in the mutants. A motile E. coli strain was mutagenized and grown in glucose and gluconate. Mutants which were able to swim into a tube containing a chemotactic attractant (aspartic acid) were isolated. Most of these mutants were able to produce beta-galactosidase in the presence of glucose and gluconate and were normal in their ability to degrade adenosine 3',5-cyclic monophosphate. Some of these mutants were defective in the glucose phosphotransferase system.