Abstract
Biological production and decay of the reactive oxygen species (ROS) hydrogen peroxide (H2O2) and superoxide (O) likely have significant effects on the cycling of trace metals and carbon in marine systems. In this study, extracellular production rates of H2O2 and O were determined for five species of marine diatoms in the presence and absence of light. Production of both ROS was measured in parallel by suspending cells on filters and measuring the ROS downstream using chemiluminescence probes. In addition, the ability of these organisms to break down O and H2O2 was examined by measuring recovery of O and H2O2 added to the influent medium. O production rates ranged from undetectable to 7.3 × 10−16 mol cell−1 h−1, while H2O2 production rates ranged from undetectable to 3.4 × 10−16 mol cell−1 h−1. Results suggest that extracellular ROS production occurs through a variety of pathways even amongst organisms of the same genus. Thalassiosira spp. produced more O in light than dark, even when the organisms were killed, indicating that O is produced via a passive photochemical process on the cell surface. The ratio of H2O2 to O production rates was consistent with production of H2O2 solely through dismutation of O for T. oceanica, while T. pseudonana made much more H2O2 than O. T. weissflogii only produced H2O2 when stressed or killed. P. tricornutum cells did not make cell-associated ROS, but did secrete H2O2-producing substances into the growth medium. In all organisms, recovery rates for killed cultures (94–100% H2O2; 10–80% O) were consistently higher than those for live cultures (65–95% H2O2; 10–50% O). While recovery rates for killed cultures in H2O2 indicate that nearly all H2O2 was degraded by active cell processes, O decay appeared to occur via a combination of active and passive processes. Overall, this study shows that the rates and pathways for ROS production and decay vary greatly among diatom species, even between those that are closely related, and as a function of light conditions.
Highlights
The reactive oxygen species (ROS), superoxide radical (O−2 ), hydrogen peroxide (H2O2), and hydroxyl radical (OH) are intermediates in the sequential one-electron reduction of oxygen to water, and are important to the biogeochemical cycling of trace metals and carbon.Photochemical production of O−2 in the marine environment has been well-studied, and occurs when photo-excited chromophoric dissolved organic matter (CDOM) transfers an electron to dissolved O2 to generate O−2 (Cooper et al, 1988; Shaked et al, 2010).Diatom Production of ROSBiological production of O−2 occurs in marine environments, but is less well-understood than photochemical production (Rose et al, 2010)
This study shows that diatoms have a wide range of values for PH2O2 that hint at a diversity of biological pathways involved in production
Phytoplankton such as diatoms may make major contributions to steady state concentrations of O−2 and H2O2 during blooms, when their abundance can increase 10-fold (Villareal et al, 2012); this corresponds to observations showing higher O−2 concentrations in Trichodesmium blooms (Rose et al, 2010)
Summary
The reactive oxygen species (ROS), superoxide radical (O−2 ), hydrogen peroxide (H2O2), and hydroxyl radical (OH) are intermediates in the sequential one-electron reduction of oxygen to water, and are important to the biogeochemical cycling of trace metals and carbon.Photochemical production of O−2 in the marine environment has been well-studied, and occurs when photo-excited chromophoric dissolved organic matter (CDOM) transfers an electron to dissolved O2 to generate O−2 (Cooper et al, 1988; Shaked et al, 2010).Diatom Production of ROSBiological production of O−2 occurs in marine environments, but is less well-understood than photochemical production (Rose et al, 2010). Photochemical production of O−2 in the marine environment has been well-studied, and occurs when photo-excited chromophoric dissolved organic matter (CDOM) transfers an electron to dissolved O2 to generate O−2 (Cooper et al, 1988; Shaked et al, 2010). The typical removal pathways for O−2 are by a dismutation reaction (Cooper and Zika, 1983; Zafiriou, 1990). By redox reactions with trace metals and organic matter (Goldstone and Voelker, 2000; Wuttig et al, 2013). H2O2 is produced through dismutation and reduction of O−2 ; it has the same photochemical and biological sources as O−2 In O−2 as a addition, H2O2 can precursor (Palenik be produced et al, 1987)
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