Dinoflagellates’ (microbial) friends and their functions

Marine phytoplankton live amongst a complex community of microbial associates that can afect their growth, physiology and behaviour. But what the relative importance of these microbial efects are, in comparison to the many other bottom-up and top-down controls of primary production, remain poorly characterised. Tis is largely because interrogating microscale interactions in natural samples is very difcult. Tis has resulted in the majority of investigations using ‘simple systems’, such as laboratory cultures with simplifed microbial communities. Nevertheless, such studies are now unravelling mechanisms by which phytoplankton and bacteria may interact. In this presentation, we report ongoing work with marine dinofagellates and their bacterial associates. Tis work has highlighted that some dinofagellates have an obligatory requirement for bacteria following periods of dormancy, but not always during vegetative growth. A bacterially-produced co-factor is suspected, but unconfrmed. Tis work, coupled with bacterial community analysis, identifed Marinobacter – a genus of oil-degrading bacteria – to be ubiquitous associates of dinofagellates and many other micro and macro-algae. Moreover, Marinobacter nearly always turn out to be benefcial in some way for the algal host. For example, production of photo-active iron-binding ligands has highlighted how bacteria may mediate enhanced iron uptake rates by phytoplankton. However, we believe Marinobacter’s importance extends beyond just producing siderophores, and one speculation is that they may represent a keystone microbial species in algal-associated communities.