The Diatom Microbiome: New Perspectives for Diatom-Bacteria Symbioses

Since their relatively recent evolution, diatoms have come to dominate today’s oceans, playing a critical role in major biogeochemical cycles, including carbon and silicon, and supporting coastal and polar food webs. A key factor underpinning diatom ecological success is their secretion of dissolved organic matter (DOM) that attracts a variety of heterotrophic bacteria in aquatic environments; in turn, these heterotrophs supply diatoms with nutrients and cofactors essential for their survival in different environmental regimes. These symbiotic exchanges occur in the diffusive boundary layer surrounding phytoplankton cells, including diatoms, known as the phycosphere. Research efforts over the past few decades have explored the nature and range of associations between diatoms and bacteria and illuminated the profound influence they can have on diatom physiology and ecology. Recent advances in genomics, microscopy, mass spectrometry, microbial cultivation, and microfluidic devices have revolutionized the study of diatom-bacteria symbiosis and promise to provide an unprecedented view of the importance of this microbial symbiosis to the oceanic ecosystem. In this chapter, we discuss DOM, alongside other nutrients, as major drivers of diatom-bacteria symbiosis, and outline new concepts in interkingdom signaling, exploring their role in diatom microbiome assembly and maintenance. We synthesize the current knowledge in light of new discoveries and highlight novel directions to further expand our understanding of diatoms and their success in the modern ocean living alongside bacteria.