Plasmids are circles of DNA that are able to replicate autonomously in many organisms - including many bacteria. Plasmids are evolutionarily important for at least two reasons:

 

1. They often encode traits that are of economic and/or medical interest - e.g. antibiotic resistance, the ability to grow on synthetic compounds, and the ability to cause disease.

2. Many can move ‘horizontally’ between bacterial cells - mediating a form of genetic transfer known as conjugation (sometimes, ‘bacterial sex’)

 

We are carrying out a study that combines the two aspects listed above. Many bacteria carry a trait known as PSK - post-segregational killing - a form of plasmid revenge, whereby plasmids use toxin-antitoxin systems to kill or inhibit bacterial cells that lose them. We are interested in the ecological basis of this trait and in the evolutionary implications of this trait. We hope to understand the selective mechanisms relevant to PSK directly, and to use this trait as a model for understanding the selection for other plasmid encoded traits. To do this we use an interactive mix of direct microbiological experiments and mathematical simulations.