Comparative distribution of antisense-RNA regulated toxin-antitoxin systems

Toxin-antitoxin (TA) systems are gene modules that appear to be widely horizontally mobile. It has been proposed that type I TA systems, with an antisense RNA-antitoxin, are less mobile than other TAs but no direct comparisons have been made. We searched for type I, II and III toxin families on chromosomes, plasmids and phages across bacterial phyla.The distribution of type I TA systems were more narrow than most type II and III system families, though this was less true of more recently discovered families.We discuss how the function and phenotypes of type I TA systems as well as biases in our databases and discovery of these modules may account for differences in their distribution.