The Effects of Glycerol, Glucose, Galactose, Lactose and Glucose with Galactose on the Induction of ß-galactosidase in Escherichia coli

Abstract

Previous work has shown that lactose, added to an Escherichia coli culture grown in M9 media + glycerol, reduces the expression of β -galactosidase. Transcription of the lac operon is normally activated in the presence of lactose. To investigate the possibility that the metabolites of lactose, glucose and galactose, were responsible for this effect, we compared a culture supplemented with lactose to one supplemented with glucose + galactose. We also examined the effect of glucose and galactose alone on β -galactosidase induction. β – galactosidase induction was determined by an enzymatic assay. Separately, glucose and galactose exerted different effects on the lac operon. Both lactose and glucose + galactose showed similar effects in reducing β -galactosidase induction, suggesting that the effects on repression seen with lactose are due to its constituent carbohydrate monomers and that the effects of glucose and galactose are additive.