Toxin Inactivation in Toxin/Antitoxin Systems

Toxin/antitoxin (TA) systems are used primarily to inhibit phage, reduce metabolic activity during stress, and maintain genetic elements. Given the extreme toxicity of some of the toxins of these TA systems, we were curious how the cell silences toxins, if the antitoxin is inactivated or when toxins are obtained without antitoxins via horizontal gene transfer. Here we find that the RalR (type I), MqsR (type II), GhoT (type V), and Hha (type VII) toxins are inactivated primarily by a mutation that inactivates the toxin promoter or via the chromosomal mutations iraM and mhpR.