Lipid mediators in marine diatoms

Diatoms are eukaryotic microalgae representing one of the major groups in the marine phytoplankton, accounting for up to 40% of annual productivity at sea. They are widely distributed in all aquatic environments, including extreme ones. To adapt and thrive in such different environments, diatoms have evolved several strategies, including the production of secondary metabolites and toxins as defence mechanisms. Despite the great ecological relevance of these organisms, the study of chemical interactions underlying intraspecific and interspecific communication is still an open field of research. To date, the best known example of chemical mediators in diatoms is represented by oxylipins. These compounds have multiple functions such as antipredator, antibacterial, infochemical and allelochemical, influencing the abundance and distribution of other species in the surrounding environments and eventually shaping the ecosystem functioning. Other lipidic compounds involved in chemical signalling in many organisms have been identified in diatoms, but their role in these microalgae is still poorly understood. In this review, we focus on lipidic secondary metabolites produced by diatoms, i.e. oxylipins, prostaglandins and sterols, their biosynthetic pathways and their established or putative role as infochemicals.