Toxin-antitoxin systems in bacteria: Apoptotic tools or metabolic regulators

The results of recent (10-12 years) research in the functions of two-gene chromosomal modules are considered and generalized. One of the genes encodes a toxin protein; the product of the other gene is an antitoxin protein. In the course of balanced bacterial growth, the toxin is constantly neutralized by the antitoxin; however, certain metabolic changes (amino acid starvation, etc.) disturb the balance and then the toxin “poisons” the cell (in most cases, by destroying mRNA). As a result, bacterial growth ceases. In accordance with one group of the data, long-term inhibition of growth of most cells results in their programmed death and destruction, corresponding to apoptosis; this allows a minor part of the population to survive due to an additional nutrient source. The results of other works show that growth inhibition is mostly reversible and the functions of the relevant gene modules are restricted to the regulation of cell metabolism, i.e., transition of bacteria to the hypometabolic state. There is also a compromise point of view. The possibilities of biotechnological applications for “toxin-antitoxin” systems are discussed.