Practice question

Diauxic growth describes biphasic exponential growth observed by Monod when Escherichia coli is cultured with two fermentable sugars such as glucose plus lactose. Glucose is consumed first, supporting rapid growth while suppressing adenylate cyclase activity, lowering intracellular cAMP levels, preventing CAP-cAMP activation, and causing inducer exclusion where unphosphorylated EIIA-Glc blocks LacY permease function. Lac enzymes remain at basal level. After glucose exhaustion, metabolic adaptation triggers lac operon induction, cAMP rises, and second exponential phase on lactose follows, separated by intermediate lag producing characteristic double sigmoidal optical density growth curve.