The creation of milk products such as cheeses and yogurts is dependent on the conversion by various anaerobic bacteria, including several Lactobacillus species, of lactose to glucose and galactose, ultimately producing lactic acid. These conversions are dependent on both permease and β-galactosidase as part of the lac operon. After selection for rapid fermentation for the production of yogurt, one Lactobacillus subspecies lost its ability to regulate lac operon expression [Lapierre, L., et al. (2002). J. Bacteriol. 184:928–935]. Would you consider it likely that in this subspecies the lac operon is on or off? What genetic events would likely contribute to the loss of regulation as described above?

Key Concepts

Lac Operon

The lac operon is a set of genes in bacteria that are involved in the metabolism of lactose. It includes genes for β-galactosidase, which breaks down lactose into glucose and galactose, and permease, which facilitates lactose entry into the cell. The operon is regulated by the presence or absence of lactose, allowing bacteria to efficiently use lactose as an energy source when available.

Gene Regulation

Gene regulation refers to the mechanisms that control the expression of genes, determining when and how much of a gene product is made. In the context of the lac operon, regulation is achieved through the binding of repressor proteins and the presence of inducers like lactose, which can activate or deactivate the operon. Loss of regulation can lead to continuous expression of the operon, regardless of lactose availability.

Mutations and Genetic Events

Mutations are changes in the DNA sequence that can affect gene function and regulation. In the case of the Lactobacillus subspecies, genetic events such as point mutations, deletions, or insertions in the regulatory regions of the lac operon could lead to a loss of regulation. These mutations may result in the operon being constitutively active (always 'on') or inactive, impacting the organism's ability to metabolize lactose effectively.