Reactive oxygen species (ROS) is a diverse group of small molecules with different reactivity, sources of production, and, ultimately, biological functions. Some of these molecules are important contributors to pathogenesis of major chronic diseases including cancer, diabetes, and atherosclerosis. Others play major roles in environmental, radiation and space biology. In normal state, specific ROS carry out homeostatic functions such as innate immunity and signaling. However, the word “ROS” is still often used in the literature as a generic term synonymous to oxidative stress. This review provides a brief description of ROS diversity, interrelations and main biological functions.

Reactive oxygen species

Reactive oxygen species (ROS) are produced ubiquitously across the tree of life. Far from being synonymous with toxicity and harm, biological ROS production is increasingly recognized for its essential functions in signaling, growth, biological interactions, and physiochemical defense systems in a diversity of organisms, spanning microbes to mammals. Part of this shift in thinking can be attributed to the wide phylogenetic distribution of specialized mechanisms for ROS production, such as NADPH oxidases, which decouple intracellular and extracellular ROS pools by directly catalyzing the reduction of oxygen in the surrounding aqueous environment. Furthermore, biological ROS production contributes substantially to natural fluxes of ROS in the ocean, thereby influencing the fate of carbon, metals, oxygen, and climate-relevant gases. Here, we review the taxonomic diversity, mechanisms, and roles of extracellular ROS production in marine bacteria, phytoplankton, seaweeds, and corals, highlighting the ecological and biogeochemical influences of this fundamental and remarkably widespread process.

Production of Extracellular Reactive Oxygen Species by Marine Biota.

The balance between sources and sinks of molecular oxygen in the oceans has greatly impacted the composition of Earth's atmosphere since the evolution of oxygenic photosynthesis, thereby exerting key influence on Earth's climate and the redox state of (sub)surface Earth. The canonical source and sink terms of the marine oxygen budget include photosynthesis, respiration, photorespiration, the Mehler reaction, and other smaller terms. However, recent advances in understanding cryptic oxygen cycling, namely the ubiquitous one-electron reduction of O2 to superoxide by microorganisms outside the cell, remains unexplored as a potential player in global oxygen dynamics. Here we show that dark extracellular superoxide production by marine microbes represents a previously unconsidered global oxygen flux and sink comparable in magnitude to other key terms. We estimate that extracellular superoxide production represents a gross oxygen sink comprising about a third of marine gross oxygen production, and a net oxygen sink amounting to 15 to 50% of that. We further demonstrate that this total marine dark extracellular superoxide flux is consistent with concentrations of superoxide in marine environments. These findings underscore prolific marine sources of reactive oxygen species and a complex and dynamic oxygen cycle in which oxygen consumption and corresponding carbon oxidation are not necessarily confined to cell membranes or exclusively related to respiration. This revised model of the marine oxygen cycle will ultimately allow for greater reconciliation among estimates of primary production and respiration and a greater mechanistic understanding of redox cycling in the ocean.

https://www.pnas.org/content/pnas/117/7/3433.full.pdf

Dark biological superoxide production as a significant flux and sink of marine dissolved oxygen.

The role of organic nutrients in structuring freshwater phytoplankton communities in a rapidly changing world.

Hedonic Price Estimates of Lake Water Quality: Valued Attribute, Instrumental Variables, and Ecological-Economic Benefits

The limiting nutrient for freshwater phytoplankton productivity can vary within and between geographic regions. Understanding how local (i.e., lake and catchment) and regional (i.e., multiple catch...

Prevalence of phytoplankton limitation by both nitrogen and phosphorus related to nutrient stoichiometry, land use, and primary producer biomass across the northeastern United States

In marine waters, ubiquitous reactive oxygen species (ROS) drive biogeochemical cycling of metals and carbon. Marine phytoplankton produce the ROS superoxide (O2-) extracellularly and can be a dominant source of O2- in natural aquatic systems. However, the cellular regulation, biological functioning, and broader ecological impacts of extracellular O2- production by marine phytoplankton remain mysterious. Here, we explored the regulation and potential roles of extracellular O2- production by a noncalcifying strain of the cosmopolitan coccolithophorid Emiliania huxleyi, a key species of marine phytoplankton that has not been examined for extracellular O2- production previously. Cell-normalized extracellular O2- production was the highest under presumably low-stress conditions during active proliferation and inversely related to cell density during exponential growth phase. Removal of extracellular O2- through addition of the O2- scavenger superoxide dismutase (SOD), however, increased growth rates, growth yields, cell biovolume, and photosynthetic efficiency (Fv/Fm ) indicating an overall physiological improvement. Thus, the presence of extracellular O2- does not directly stimulate E. huxleyi proliferation, as previously suggested for other phytoplankton, bacteria, fungi, and protists. Extracellular O2- production decreased in the dark, suggesting a connection with photosynthetic processes. Taken together, the tight regulation of this stress independent production of extracellular O2- by E. huxleyi suggests that it could be involved in fundamental photophysiological processes.

/pdf/dynamic-regulation-of-extracellular-superoxide-production-by-1sebpvjk61.pdf

Dynamic Regulation of Extracellular Superoxide Production by the Coccolithophore Emiliania huxleyi (CCMP 374).

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Prevalence of phytoplankton limitation by both nitrogen and phosphorus related to nutrient stoichiometry, land use, and primary producer biomass across the northeastern United States

Dynamic Regulation of Extracellular Superoxide Production by the Coccolithophore Emiliania huxleyi (CCMP 374).