What physiological function is induced in E. coli following glucose depletion?

Following glucose depletion, E. coli induces the lac operon, which is responsible for the transport and metabolism of lactose. The lac operon contains genes coding for lactose permease and beta-galactosidase, enzymes that are crucial for utilizing lactose when glucose, the preferred carbon source, is scarce.

When glucose is available, the cAMP levels are low, which inhibits the expression of the lac operon. However, upon glucose depletion, the cAMP levels rise, leading to the activation of the catabolite activator protein (CAP) which, when combined with cAMP, enhances the binding of RNA polymerase to the promoter of the lac operon. This results in increased expression of genes necessary for lactose utilization. Thus, E. coli transitions from glucose metabolism to using lactose, making the induction of the lac operon a physiological response to glucose scarcity.

This metabolic adaptation highlights E. coli's ability to efficiently utilize available nutrients and demonstrates the regulation of gene expression in response to environmental changes.