Abstract:Toxin-antitoxin systems (TAs) are prevalent genetic elements in bacteria, archaea, and prophages, which are usually composed of a growth-inhibiting toxin and its cognate antitoxin. Toxins are stable in bacterial cells, while antitoxins are prone to be degraded by the ATP-dependent proteases. Most toxins are proteins and have enzyme activity, which inhibit bacterial growth by affecting important life activities such as protein translation and DNA replication. Antitoxins are either proteins or noncoding RNAs that neutralize the toxicity of toxins to bacteria in diverse ways. The available studies have demonstrated that TAs function as plasmid-stabilization elements, provide defense against phages, and promote biofilm formation. As the research deepens, increasing novel TAs have been discovered, which improves our understanding of TAs. At present, the classification of TAs has been extended to types Ⅰ-Ⅷ. This paper summarizes the recent discoveries of new TAs and focuses on the type Ⅶ TA in which the enzymatic antitoxin chemically modifies the toxin to neutralize it. Since TAs are closely associated with the pathogenicity of pathogenic microorganisms, in-depth study of these TAs can provide new targets for the treatment of drug-resistant microorganisms.
