Biological Functions of Type II Toxin-Antitoxin Systems in Bacteria

Abstract

After the first discovery in the 1980s in F-plasmids as a plasmid maintenance system, a myriad of toxin-antitoxin (TA) systems has been identified in bacterial chromosomes and mobile genetic elements (MGEs), including plasmids and bacteriophages. TA systems are small genetic modules that encode a toxin and its antidote and can be divided into seven types based on the nature of the antitoxin molecules and their mechanism of action to neutralise toxins. Among them, type II TA systems are widely distributed in chromosomes and plasmids and the best studied so far. Maintaining genetic material may be the major function of type II TA systems associated with MGEs, but the chromosomal TA systems contribute largely to functions associated with bacterial physiology, including the management of different stresses, virulence and pathogenesis. Due to growing interest in TA research, extensive work has been conducted in recent decades to better understand the physiological roles of these chromosomally encoded modules. However, there are still controversies about some of the functions associated with different TA systems. This review will discuss the most current findings and the bona fide functions of bacterial type II TA systems.

Plasmidome of Listeria spp.—The repA-Family Business

“…In addition, putative toxins of type III TA systems were Many repA-family plasmids (but none of the small Listeria RCR plasmids) contain additional stabilization modules, which act by a mechanism involving post-segregational killing of plasmid-less cells. Such systems are usually two-gene operons, encoding a stable toxic protein and a labile antitoxin that neutralizes the toxin's activity [30].…”

Plasmid-Mediated Stabilization of Prophages

“…2 ). Each plasmid encodes at least one type II toxin-antitoxin system, all of which are unique and predicted to be involved in plasmid maintenance ( 39 ). pSpoCB-1 possesses the only flagellar gene cluster in the genome (similar to other roseobacter plasmids [ 18 , 40 ]), cytochrome c oxidase genes, and several genes implicated in cellular stress responses (e.g., beta lactamase, thioredoxin peroxidase, and a cbb3-type cytochrome c oxidase).…”

A centimeter-long bacterium with DNA compartmentalized in membrane-bound organelles

“…T. magnifica genomes were riddled with a myriad of toxin/antitoxin systems (Table S11). While some of these systems may be involved in maintaining genetic material, such as mobile genetic elements, others may play regulatory roles in stress response, adaptation, as well as contribute to the complex lifestyle ( 72 ).…”