Lag phase in diauxic growth is due to
During diauxic transition, glucose depletion triggers transient growth arrest because cells initially lack sufficient lactose permease and beta-galactosidase to sustain energy generation from lactose. Lag corresponds to interval required for residual cAMP elevation, CAP-cAMP complex binding upstream of promoter, derepression of LacI repressor by allolactose derived from trace lactose entry through basal permease molecules, transcription of lacZYA polycistronic mRNA, translation, membrane insertion of functional LacY transporters, and establishment of positive feedback loop that amplifies intracellular inducer concentration. Once enzymatic capacity accumulates adequately, exponential growth on lactose resumes, so pause reflects induction kinetics rather than cell death or mutation event.
Ref: Journal of Bacteriology General Stress Sigma during diauxic shift – lag reflects lac permease and β-galactosidase induction after glucose exhaustion.