Cell explosions: single cell death triggers an avoidance response in local populations of the ecologically prominent phytoplankton genus Micromonas

The global phytoplankton community, comprised of aquatic photosynthetic organisms, is acknowledged for being responsible for half of the global oxygen production Prominent among these is the pico-eukaryote Micromonas commoda (formally Micromonas pusilla of the genus Micromonas), which can be found in marine and coastal environments across the globe. Cell death of phytoplankton has been identified as contributing to the largest carbon transfers on the planet moving 109 tonnes of carbon in the oceans every day. During a cell death organic matter is released into the local environment which can act as both a food source and a warning signal for nearby organisms. Here we present a novel motility response to single cell death in populations of Micromonas sp., where the death of a single cell releases a chemical patch triggers surrounding cells to escape the immediate affected area. These so-called "burst events" are then modelled and compared with a spherically symmetric diffusing patch which is found to faithfully reproduce the observed behaviour. Finally, laser ablation of single cells reproduces the observed avoidance response, confirming that Micromonas sp. has evolved a specific motility response in order to escape harmful environments for example nearby predator-prey interactions or virus lysis induced cell death.