EAPS

Special Seminar: "Nutrients and Toxic Signals: The Role of Phytoplankton in Cryptic Biogeochemical Cycles"
Date Time Location
April 27th, 2015 3:45pm-5:00pm 54-915
Speaker: Julia Diaz, Postdoctoral Fellow, Department of Marine Chemistry and Geochemistry, WHOI

"Nutrients and Toxic Signals: The Role of Phytoplankton in Cryptic Biogeochemical Cycles"

Microorganisms control the geochemistry of our planet via metabolic pathways that link the global cycles of key elements, such as carbon, nitrogen, phosphorus, oxygen, and metals. However, many biogeochemical transformations are cryptic. Cryptic biogeochemistry involves a chemical species with an exceedingly low residence time, typically driven by high rates of reactive consumption. Based on their intense reactivity, cryptic chemicals can profoundly alter the natural environment. But for the same reason, they are usually present at low concentrations, which masks their importance and makes them difficult to detect directly. Identifying and understanding the cryptic biogeochemistry that shapes the natural world therefore remains a fundamental challenge. In this talk, I will present results on the biogeochemical dynamics of two cryptic chemicals: superoxide, a form of reactive oxygen; and polyphosphate (poly-P), a polymer of three or more phosphate molecules. These chemical species play an important role in phytoplankton nutrient acquisition, population dynamics, and ultimately carbon sequestration and therefore climate. By pairing field work with phytoplankton cultivation, we have identified physiological pathways and molecular-level targets that underpin the cryptic biogeochemistry of superoxide and polyphosphate. An emerging theme is the discovery of potentially overlooked cell-free and cell surface-associated exoenzymes that catalyze the rapid transformation of these chemicals. Since these exoenzymes may be more stable than the chemicals they react with, tracking their regulation, abundance, and activity may provide unique windows into cryptic biogeochemistry in diverse marine systems. Future work has the potential to reveal cryptic biogeochemical pathways that can help explain enduring oceanographic mysteries, including the rise and fall of phytoplankton blooms and widespread iron limitation in high nutrient low chlorophyll (HNLC) regions.

4:00PM in 54-915, reception preceding seminar at 3:45. All are welcome to attend.