Dynamics and consequences of extracellular superoxide in marine systems
Reactive oxygen species (ROS) are key players in the biogeochemistry of the ocean, where they have a critical role in the degradation of carbon, cycling of metals, and health of biotic systems. ROS are, in fact, both detrimental and beneficial to life. For instance, at low concentrations the ROS superoxide mediates a number of essential physiological processes, including cell differentiation, signaling, and defense. At high concentrations, superoxide degrades essential biomolecules and initiates programmed cell death.
Marine microbes, including bacteria, cyanobacteria and diatoms, have recently been shown to produce substantial levels of extracellular superoxide at rates that greatly contribute to in situ superoxide fluxes within the ocean. Yet, little is known about the physiological basis for extracellular superoxide production in marine microbes, how this production is regulated, and the impact of this production on global ROS levels and trace metal cycling. This presentation will summarize our current progress in addressing these knowledge gaps through investigations of superoxide dynamics within laboratory and shipboard incubations coupled with field-based measurements.
In total, we find widespread dark production of superoxide by marine organisms that is tightly controlled at the cellular level and having a possible link to growth regulation. Further, extrapolation of biologial superoxide production rates indicates that oxygen reduction to superoxide could represent an overlooked O2 sink within the ocean, accounting for a substantial portion of the marine O2 budget and thus having implications for global biogeochemical cycling.