Killing in response to competition stabilises synthetic microbial consortia

The scale of the synthetic biological systems we can produce is limited by the burden that host microbes can bear. Division-of-labour can spread that burden across a community of cells but competitive exclusion inevitably leads to the removal of less fit community members over time. Here, we leverage competitive exclusion to develop a novel system to stabilise multi-species communities by engineering the dynamic secretion of a toxin. We show mathematically that such a system can produce stable populations with a composition that is tunable by easily controllable parameters. We implement the system in Escherichia coli and demonstrate community dynamics in a chemostat. This is the first system to use competitive exclusion to create a stable two-species consortia and the first to only require the engineering of a single strain.