A microbial source of phosphonates in oligotrophic marine systems

Phosphonates, compounds with a carbon-phosphorus bond, are a key component of the marine dissolved organic phosphorus pool(1). These compounds serve as a phosphorus source for primary producers, including the nitrogen-fixing cyanobacteria Trichodesmium(2). Phosphonates can therefore support marine primary production, as well as climate-driven increases in marine nitrogen fixation(3), carbon sequestration(4) and possibly methane production, through the breakdown of methylphosphonate(5). Despite their importance, the source of phosphonates to the open ocean has remained uncertain. Here, we use solid-state nuclear magnetic resonance spectroscopy to screen for the presence of phosphonates in cultured strains of Trichodesmium erythraeum. We show that phosphonates comprise an average of 10% of the cellular particulate phosphorus pool in this species. We therefore suggest that these cyanobacteria produce phosphonates, and might be a significant source of these compounds in the ocean, particularly in nutrient-poor regions, where Trichodesmium blooms occur. Given that Trichodesmium also thrives in a warm, carbon-dioxide-rich environment(3), phosphonate production may increase in the future. This, in turn, might select for a microbial community that can use phosphonate, and could have implications for nitrogen fixation, carbon sequestration and greenhouse-gas production.