Stripping the molecular basis of marine microbial interactions

Marine primary production is mainly driven by microscopic phytoplankton since phototrophic picocyanobacteria and picoeukaryotes contribute to almost all photosynthesis that takes place in the vast photic zones of the oligotrophic open ocean. Picocyanobacteria, green algae, diatoms and prymnesiophytes are the numerically most abundant primary producers on Earth and the abundance of some of them is predicted to increase due to climate change. Marine planktonic microorganisms generally show stable cell numbers, with growth and loss largely balanced. Ultimately, all primary production will be converted into particulate or dissolved organic matter (DOM) which becomes the main source of carbon and energy for the complex marine food web (mainly, heterotrophic bacteria). DOM is thought to be generated by cell death, viral lysis and inefficient grazing, but also living organisms are known to be, per se, inevitably or 'intentionally' leaky, e.g. through the production of extracellular vesicles, active efflux processes or, simply, permeable membrane leakage. In this sense, phytoplankton drive bacterial community dynamics as they are the main suppliers of organic matter. We recently observed that nutrient exchange plays a key role in phototroph-heterotroph interactions and current work in the group has shown that different phytoplankton species generate a variety of metabolites that condition the response and behaviour of their co-occurring heterotrophic bacteria. Of these, phosphorus is of notable import. Recent modelling has found preferential remineralisation of phosphorus to increase the strength of the biological pump and global net primary production in general, including increased utilisation of other metabolites such as nitrogen. Hence, this project aims to dissect the key metabolites produced in these systems and determine how these exert an influence on other species.