183 research outputs found
Spectroscopic insights into ferromanganese crust formation and diagenesis
No full textAuthor Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(11), (2020): e2020GC009074, doi:10.1029/2020GC009074.Marine ferromanganese deposits, often called the scavengers of the sea, adsorb and coprecipitate with a wide range of metals of great interest for paleo‐environmental reconstructions and economic geology. The long (up to ∼75 Ma), near‐continuous record of seawater chemistry afforded by ferromanganese deposits offers much historical information about the global ocean and surface earth including crustal processes, mantle processes, ocean circulation, and biogeochemical cycles. The extent to which the ferromanganese deposits hosting these geochemical proxies undergo diagenesis on the seafloor, however, remains an important and challenging factor in assessing the fidelity of such records. In this study, we employ multiple X‐ray techniques including micro–X‐ray fluorescence, bulk and micro–X‐ray absorption spectroscopy, and X‐ray powder diffraction to probe the structural, compositional, redox, and mineral changes within a single ferromanganese crust. These techniques illuminate a complex two‐dimensional structure characterized by crust growth controlled by the availability of manganese (Mn), a dynamic range in Mn oxidation state from +3.4 to +4.0, changes in Mn mineralogy over time, and recrystallization in the lower phosphatized portions of the crust. Iron (Fe) similarly demonstrates spatial complexity with respect to concentration and mineralogy, but lacks the dynamic range of oxidation state seen for Mn. Micrometer‐scale measurements of metal abundances reveal complex element associations between trace elements and the two major oxide phases, which are not typically resolvable via bulk analytical methods. These findings provide evidence of post‐depositional processes altering chemistry and mineralogy, and provide important geochemical context for the interpretation of element and isotopic records in ferromanganese crusts.This research is supported by NASA Exobiology NNX15AM046 to Scott D. Wankel and Colleen M. Hansel, NASA NESSF NNX15AR62H to Kevin M. Sutherland, and WHOI Ocean Exploration Institute to Colleen M. Hansel. The Stanford Synchrotron Radiation Lightsource was utilized in this study. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE‐AC02‐76SF00515.2021-04-2
jamesrco/LipidPhotoOxBox: LipidPhotoOxBox v1.0.0
No full textInitial release of data and code in LipidPhotoOxBox to support Collins, J. R., H. F. Fredricks, J. M. Diaz, J. S. Bowman, C. P. Ward, C. Moreno, K. Longnecker, A. Marchetti, C. M. Hansel, H. W. Ducklow, and B. A. S. Van Mooy (2017), The diverse products and biogeochemical significance of lipid photooxidation in coastal surface waters of West Antarctica
Tight regulation of extracellular superoxide points to its vital role in the physiology of the globally relevant Roseobacter clade.
No full text© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hansel, C. M., Diaz, J. M., & Plummer, S.. Tight regulation of extracellular superoxide points to its vital role in the physiology of the globally relevant Roseobacter clade. Mbio, 10(2), (2019):e02668-18, doi:10.1128/mBio.02668-18.There is a growing appreciation within animal and plant physiology that the reactive oxygen species (ROS) superoxide is not only detrimental but also essential for life. Yet, despite widespread production of extracellular superoxide by healthy bacteria and phytoplankton, this molecule remains associated with stress and death. Here, we quantify extracellular superoxide production by seven ecologically diverse bacteria within the Roseobacter clade and specifically target the link between extracellular superoxide and physiology for two species. We reveal for all species a strong inverse relationship between cell-normalized superoxide production rates and cell number. For exponentially growing cells of Ruegeria pomeroyi DSS-3 and Roseobacter sp. strain AzwK-3b, we show that superoxide levels are regulated in response to cell density through rapid modulation of gross production and not decay. Over a life cycle of batch cultures, extracellular superoxide levels are tightly regulated through a balance of both production and decay processes allowing for nearly constant levels of superoxide during active growth and minimal levels upon entering stationary phase. Further, removal of superoxide through the addition of exogenous superoxide dismutase during growth leads to significant growth inhibition. Overall, these results point to tight regulation of extracellular superoxide in representative members of the Roseobacter clade, consistent with a role for superoxide in growth regulation as widely acknowledged in fungal, animal, and plant physiology.We thank Mary Ann Moran and Alison Buchan for providing Roseobacter cultures, Kevin Sutherland for providing helpful feedback on the manuscript, and Elizabeth Harvey for use of her flow cytometer.
This research was supported by NSF OCE-1355720 and a WHOI Independent Study Award (27005303) to C.M.H., as well as a Junior Faculty Seed Grant from the University of Georgia Research Foundation to J.M.D. and a National Science Foundation Graduate Research Fellowship to S.P
Heterotrophic bacteria exhibit a wide range of rates of extracellular production and decay of hydrogen peroxide
No full text© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bond, R. J., Hansel, C. M., & Voelker, B. M. Heterotrophic bacteria exhibit a wide range of rates of extracellular production and decay of hydrogen peroxide. Frontiers in Marine Science, 7, (2020): 72, doi:10.3389/fmars.2020.00072.Bacteria have been implicated as both a source and sink of hydrogen peroxide (H2O2), a reactive oxygen species which can both impact microbial growth and participate in the geochemical cycling of trace metals and carbon in natural waters. In this study, simultaneous H2O2 production and decay by twelve species of heterotrophic bacteria were evaluated in both batch and flow-through incubations. While wide species-to-species variability of cell-normalized H2O2 decay rate coefficients [2 × 10–8 to 5 × 10–6 hr–1 (cell mL–1)–1] was observed, these rate coefficients were relatively consistent for a given bacterial species. By contrast, observed production rates (below detection limit to 3 × 102 amol cell–1 hr–1) were more variable even for the same species. Variations based on incubation conditions in some bacterial strains suggest that external conditions may impact extracellular H2O2 levels either through increased extracellular production or leakage of intracellular H2O2. Comparison of H2O2 production rates to previously determined superoxide (O2–) production rates suggests that O2– and H2O2 production are not necessarily linked. Rates measured in this study indicate that bacteria could account for a majority of H2O2 decay observed in aqueous systems but likely only make a modest contribution to dark H2O2 production.This research was supported by NSF grant OCE-1131734/1246174 to BV and CH
Exploring the role of reactive oxygen species (ROS) in marine ecosystem health and function
No full textSubmitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.With the rapid decline of coastal ecosystems such as coral reefs and seagrasses, it is crucial to better understand the health of these ecosystem to prevent future loss. Reactive oxygen speices (ROS), such as superoxide and hydrogen peroxide, play an
underappreciated role in both organism health and ecosystem biogeochemical cycles. This thesis lays the foundation to measure and identify ROS production by coral in situ and through genomic analysis while also highlighting the important role that ROS can play within biogeochemical cycling within seagrass ecosystems. To measure in situ extracellular superoxide, we develop the first DIver-operated Submersible Chemiluminescent sensOr (DISCO), enabling high resolution, non-invasive measurements in real time. We further refine DISCO by making it more compact, user-friendly, adaptable, and robust, enabling measurements of superoxide across a diversity of environments. Using DISCO, I observe species-specific variation in extracellular superoxide concentrations associated with healthy coral. Despite these variations across species, bioinformatic analysis of coral proteins reveal that nearly all coral species have the extracellular superoxide-producing enzyme NADPH oxidase (NOX), and thus the genetic potential to produce extracellular superoxide. This suggests that coral species likely exhibit differential NOX regulation and expression as a function of physiological responses to external stressors, which may play a role in coral immunity. I then turn to seagrass ecosystems, where I observe rapid hydrogen peroxide production and decay through predominantly reductive pathways. This has implications on the environmental redox state and biogeochemical cycling, impacting the ecosystem services that seagrasses provide to marine environments and coastal communities. Overall, this thesis highlights the potential role that ROS may be playing in organism and ecosystem health and lays the groundwork to further develop ROS as a tool to protect these coastal ecosystems against further degradation.Funding for this work was provided by the following grants: NSF GRFP (2016230168), Schmidt Marine Technology Partners (G-1801-57385 andG-2010-59878), WHOI Ocean Ventures Fund (2020 and 2021), and the MIT Wellington and Irene Loh Fund Fellowship (4000111995)
Dark biological superoxide production as a significant flux and sink of marine dissolved oxygen
No full text© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sutherland, K. M., Wankel, S. D., & Hansel, C. M. Dark biological superoxide production as a significant flux and sink of marine dissolved oxygen. Proceedings of the National Academy of Sciences of the United States of America, 117(7), (2020): 3433-3439, doi:10.1073/pnas.1912313117.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.This work was supported by NASA Earth and Space Science Fellowship NNX15AR62H to K.M.S., NASA Exobiology grant NNX15AM04G to S.D.W. and C.M.H., and NSF Division of Ocean Sciences grant 1355720 to C.M.H. This research was further supported in part by Hanse-Wissenschaftskolleg Institute of Advanced Study fellowships to C.M.H. and S.D.W. We thank Danielle Hicks for assistance with figures and Community Earth Systems Model (CESM) Large Ensemble Project for the availability and use of its data product. The CESM project is primarily supported by the NSF
Dynamic regulation of extracellular superoxide production by the coccolithophore Emiliania huxleyi (CCMP 374)
No full text© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Plummeer, S., Taylor, A. E., Harvey, E. L., Hansel, C. M., & Diaz, J. M. Dynamic regulation of extracellular superoxide production by the coccolithophore Emiliania huxleyi (CCMP 374). Frontiers in Microbiology, 10, (2019): 1546, doi: 10.3389/fmicb.2019.01546.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.This research was supported by a Junior Faculty Seed Grant from the University of Georgia Research Foundation (JD), a National Science Foundation (NSF) Graduate Research Fellowship (SP), and NSF grant OCE-1355720 (CH). The FlowCam® and FIRe were purchased through a NSF Equipment Improvement Grant (1624593)
Manganese in Marine Microbiology
No full textThe importance of manganese in the physiology of marine microbes, the biogeochemistry of the ocean and the health of microbial communities of past and present is emerging. Manganese is distributed widely throughout the global ocean, taking the form of an essential antioxidant (Mn2 +), a potent oxidant (Mn3 +) and strong adsorbent (Mn oxides) sequestering disproportionately high levels of trace metals and nutrients in comparison to the surrounding seawater. Manganese is, in fact, linked to nearly all other elemental cycles and intricately involved in the health, metabolism and function of the ocean's microbiome. Here, we briefly review the diversity of microbes and pathways responsible for the transformation of Mn within the three Mn pools and their distribution within the marine environment. Despite decades of interrogation, we still have much to learn about the players, mechanisms and consequences of the Mn cycle, and new and exciting discoveries are being made at a rapid rate. What is clear is the dynamic and ever-inspiring complexity of reactions involving Mn, and the acknowledgement that microorganisms are the catalytic engine driving the Mn cycle
Implications of widespread dark production and decay of reactive oxygen species in natural waters
No full text2015 Fall.Includes illustrations, color maps.Includes bibliographical references.Light dependent and independent reactions produce and consume reactive oxygen species (ROS), including hydrogen peroxide (H2O2) and superoxide (O2-), in natural waters. ROS can act as oxidants or reductants to biologically important metals such as Fe, Cu, and Mn influencing their bioavailability. ROS produced in natural waters have also been linked to global phenomena such as harmful algal bloom fish kills and coral bleaching. In this thesis, we focus on the light independent (dark) reactions of ROS that are produced and decomposed by particle-associated processes, most likely microorganisms. However, before microorganisms can be implicated in ROS reactions we need to understand where, why, and how microorganisms as well as abiotic processes produce and decompose ROS. Ecological and geochemical stress factors that trigger ROS production and decomposition in natural waters are largely unknown. Therefore, we set out to measure the temporal and spatial variability of dark H2O2 production rates (PH2O2) and dark decay rate coefficients (kloss,H2O2) in freshwaters with a range of trophic states. Production rates were found to be comparable to production by photochemical processes. Furthermore, kloss,H2O2 correlated well with biological indicators (chlorophyll and cell counts) while PH2O2 did not. This suggests that while microorganisms are a common sink of H2O2, dark production may vary with microbial composition. We suspect that both a lake’s trophic state and the specific microbial consortia present in the system, at a given time, lead to the observed variability of ROS production in freshwater. The method for measuring dark PH2O2 in project one, which utilized an isotope tracer (H218O2), proved tedious, costly, and time consuming. Therefore, we used Amplex Red (AR) oxidation by H2O2 in the presence of horseradish peroxidase (HRP) catalyst as an effective alternative. We show that AR/HRP is suitable for measuring dark PH2O2 in freshwater by examining possible false positive and negative interferences, and methods to eliminate them. Catalase and HRP-free controls helped validate the AR method and revealed dark PH2O2 values of comparable magnitude and natural variability as previous studies. The dark redox cycling of mercury (Hg), especially the production of Hg(II), can lead to the formation of toxic methylated Hg compounds. Because dark reactions of Hg are largely an enigma and ROS are known to affect the redox cycling of metals in the ocean (e.g. Cu and Mn), we set out to understand if O2- plays a role in the dark biogeochemical cycle of Hg. Here, we measured O2- oxidation and reduction of Hg in filtered coastal (Vineyard Sound) seawater. O2- appeared to indirectly oxidize Hg0 in two seawater samples and O2- reduced Hg(II) in one seawater sample. We did not observe evidence of oxidation or reduction of Hg via secondary O2- reactions involving Mn, Cu, and nicotinamide adenine dinucleotide (NADH). However, our samples were filtered, and the proximity of NADH to cell surfaces may reveal a potential biological mechanism of Hg(II) reduction. The calculated reduction rate constant of Hg(II), 6.9 (3.1) x102 M-1 s-1, would cause a Hg(II) reduction rate of ~1% day-1 similar to the rate observed in previous studies of dark microbial Hg(II) reduction. Our study suggests that O2- may play an important role in the dark biogeochemical cycling of Hg in coastal ocean waters by indirectly oxidizing Hg0 and slowly reducing Hg(II)
Oxygen consumption, hydrogen accumulation, iron accumulation and sulfate reduction measured in incubations of sediment collected from the intertidal sandbank Janssand
No full textThis data set was collected from incubations of sediment collected from the intertidal sandbank Janssand, behind the back barrier island Spiekeroog, in the German Wadden Sea. The rate of oxygen consumption (microsensor), hydrogen accumulation (GC), iron accumulation (ferrozine, chlorometric), and sulfate reduction (35S sulfate + acid-chromium distillation) were all measured in constantly mixed slurries, with and without the ROS-removing enzymes superoxide dismutase and catalase. It additionally includes depth profiles of oxygen and hydrogen peroxide in cores, determined with amperometric microsensors
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