The E.coli bacteria utilize glucose and lactose as a substrate to produce various metabolites used to survive.
The bacteria use lac operon which represents a sequence of various genes aligned in a manner to use lactose as a substrate as the most favoured substrate is glucose.
The glucose metabolites regulate the transcription of the lactose operon as the presence of glucose prevent the production of cAMP which shuts off the lac operon even in the presence of the lactose.
When the glucose level is low in medium, the level of cAMP increase which binds with CAP and then activates the lac operon whereas when the glucose level is high, then the low level of cAMP does not activate the lac operon.
