The repression of constitutive β-galactosidase in Escherichia coli by glucose and other carbon sources

Abstract

When Escherichia coli is grown in flask culture with various C sources, the activity of constitutive [beta]-galactosidase is correlated with the doubling time of the culture; the poorer the C source the higher is the enzyme activity. When bacteria are transferred from a flask to a continuous-culture apparatus and grown in a N2-limiting medium (i.e with excess of C source) the formation of the enzyme is severely repressed. The effect of glucose as a repressor is not unique. Under appropriate conditions of growth all utilizable C sources act as repressors. The repression produced by C compounds is not reversed by methyl [beta]-D-thiogalactoside (an inducer of the enzyme in wild-type bacteria). It is concluded that the synthesis of inducible [beta]-galactosidase in wild-type E. coli is controlled by 2 distinct types of repressor, 1 of which is still able to function in the constitutive mutant.