The elusive chemical currencies of the microbial loop

Marine dissolved organic matter (DOM) acts as a critical control on Earth’s climate by simultaneously serving as a reservoir for long-term carbon storage and as the fuel of marine microbes. DOM is a heterogenous soup comprised of thousands of diverse organic molecules that reflect a spectrum of reactivity. Labile DOM is the most reactive and is comprised of metabolites, the products of biological metabolism, which act as chemical currencies traded by marine microbes through a tightly regulated network. While the flux of carbon through this network is one of the largest annual turnovers of carbon on Earth, labile DOM has eluded oceanographers for decades due to its short half-life of minutes to days. Recent advances in high-resolution mass spectrometry have enabled direct detection of these chemical currencies. In this talk, I will present my research which aims to quantify the composition and activity of labile DOM alongside the biological mechanisms regulating its flux. I will first present a depth-resolved time-series in the oligotrophic Atlantic Ocean that links metabolites to prokaryotic sources and sinks, and then specifically focus on the mechanisms controlling the production of a model marine metabolite, dimethylsulfoniopropionate. I will also highlight a new stable isotope approach for tracking macronutrient-containing metabolites through the microbial loop. The work presented will provide molecular-level insights with global scale implications for DOM biogeochemistry.