The redox fate of hydrogen peroxide in the marine water column

Abstract

Marine microbes produce extracellular reactive oxygen species (ROS) such as superoxide and hydrogen peroxide (H 2 O 2 ) as a result of regulated and nonregulated physiological and metabolic reactions. ROS production can be a sink and cryptic recycling flux of dissolved oxygen that may rival other key fluxes in the global oxygen cycle; however, the low abundance and high turnover rate of ROS makes this figure difficult to constrain. One key step in determining the disparity between the gross production of ROS and the net sink of dissolved oxygen lies in understanding the degradation pathways of H 2 O 2 in the marine water column. In this study, we use isotope-labeling techniques to determine the redox fate of H 2 O 2 in a range of marine environments off the West Coast of California. We find that H 2 O 2 reduction is greater than or equal to H 2 O 2 oxidation at most sampled depths, with notable exceptions in some surface and intermediate water depths. The observation that H 2 O 2 oxidation can exceed reduction in the dark ocean indicates the presence of an oxidizing decay pathway that is not among the known suite of microbially mediated enzymatic pathways (i.e., catalase and peroxidase), pointing to an abiotic and/or a nonenzymatic decay pathway at intermediate water depths. These results highlight the complexity and heterogeneity of ROS decay pathways in natural waters and their unconstrained regulation of oxygen levels within the ocean.2 and H 2 O 2 have been observed in both freshwater and seawater, and have been found to result directly

Depth-resolved photochemical production of hydrogen peroxide in the global ocean using remotely sensed ocean color

“…While the oxygenwater redox pair controls redox conditions over longgeological timescales, the situation is more complex, especially on timescales at which many biogeochemical processes occur (Rose, 2016). Along the four-electron pathway between oxygen and water are a set of reactive oxygen species (ROS), namely superoxide (O 2 − ), hydrogen peroxide (H 2 O 2 ) and hydroxyl radical (OH • ), that individually participate in critical redox chemistry (Petasne and Zika, 1987;Sawyer, 1991;Wuttig et al, 2013;Sutherland et al, 2021), and ultimately have significant impacts on the biogeochemical cycling of essential trace elements and reduced carbon in the ocean (Zepp et al, 1992;Scully et al, 2003;White et al, 2003;Rose and Waite, 2006;Rose, 2016). The low seawater concentrations of these ROS (at fM to nM levels) reflect a balance of sources and sinks for each ROS in the system, revealing just how fast the redox cycle spins (Haag and Hoigne, 1986;Mopper and Zhou, 1990;Goldstone and Voelker, 2000).…”

“…It is currently unclear what, if any, changes in observed rates and pathways result from sunrise turning the nighttime into the day, with its myriad of UVR-generated chemical transients. While reduction (via catalase or peroxidase) is typically the dominant pathway for H 2 O 2 decay, oxidation pathways have been reported to exceed reduction in some surface coastal waters, suggesting contribution of unknown abiotic or metabolic pathways (Sutherland et al, 2021).…”

Exploring the role of reactive oxygen species (ROS) in marine ecosystem health and function

“…Superoxide can undergo catalyzed and uncatalyzed dismutation to form hydrogen peroxide, which has a longer half-life spanning hours to days (Armoza-Zvuloni and Shaked, 2014). Hydrogen peroxide can react with iron (Fenton reaction) to form the highly reactive hydroxyl radical ( • OH) or decay through several pathways that are mostly mediated by enzymes such as catalase and peroxidase (Moffett and Zafiriou, 1993;Winterbourn, 2013;Sutherland et al, 2021). Catalase dismutates hydrogen peroxide to water and oxygen, while peroxidase decays hydrogen peroxide to water.…”

“…Therefore, it is valuable to understand the controls on various biogeochemical cycles and the system redox state, which will have direct bearing on the fate of carbon. Reactive oxygen species (ROS) are emerging as major players influencing the redox state and biogeochemistry of marine ecosystems Wuttig et al, 2013;Sutherland et al, 2021). Yet, ROS associated with seagrass and within seagrass meadows have only been minimally investigated.…”

“…Although thought to be less significant of a decay flux compared to microbial processes (Moffett and Zafiriou, 1993), hydrogen peroxide can also be degraded through both oxidation and reduction reactions with trace elements (cobalt, nickel, iron, copper, manganese) (Moffett and Zika, 1987;Millero and Sotolongo, 1989;Sunda and Huntsman, 1997;Hansel, 2017), organic matter (CDOM, DOC) (Kieber and Blough, 1990;Pullin et al, 2004;Lester et al, 2013), and other compounds (N, P, and O) Sutherland et al, 2021). It is noteworthy that these constituents can also act with similar stoichiometries as the microbially mediated processes (Dole et al, 1952).…”