Data from: The role of bacteriocins as selfish genetic elements

Bacteria produce a wide arsenal of toxic compounds in order to kill
competing species. Bacteriocins, protein-based toxins produced by nearly
all bacteria, have generally been considered a ubiquitous anti-competitor
strategy, used to kill competing bacterial strains. Some of these
bacteriocins are encoded on plasmids, which also code for closely linked
immunity compounds (thereby rendering toxin producing cells immune to
their own toxin). However, the production of bacteriocins can also be
interpreted as a means to promote plasmid stability by preferentially
selecting for cells carrying the plasmid. If, for example, a cell were to
lose the plasmid, it would no longer produce the immunity compound and
would be killed by its bacteriocin-producing clone mates. In this respect,
bacteriocins can be regarded as similar to previously described
toxin–antitoxin systems that are able promote the stable transmission of
plasmids to daughter cells. In order to test this prediction, we carried
out an experimental evolution study using the bacterium Escherichia coli,
finding that bacteriocins can indeed select for the stable maintenance of
plasmids. This suggests that bacteriocins can act primarily as selfish
genetic elements promoting their own transmission in the population, which
may help explain their unique ecology and evolution.