How mobile are type I toxin-antitoxin systems?

What is it about?

Toxin-antitoxin (TA) systems are gene modules that appear to be horizontally mobile across a wide range of prokaryotes. The systems consist of a small toxin protein and an RNA which binds to the transcript for the protein and triggers its degradation. If the system is lost, the antitoxin RNA degrades faster than the RNA coding for the toxin, causing the toxin to be produced and the cell to die or stop growing. As a result, once cells become hosts to these TA systems they can't lost them. It has been proposed that type I TA systems are less capable of jumping between different bacteria than other types, and instead rely mostly on inheritance, however this hasn't been well tested. We used profile hidden Markov models, a powerful tool for identifying distantly related proteins, to scan phage, plasmids and bacterial chromosomes on the European Nucleotide Archive and test this theory. We found that consistent with previous observations, type I TA systems showed less spread across diverse bacteria than type II and III systems, but that this was more true for TA systems that had been discovered a long time ago than ones discovered recently.

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