scholarly journals Common physiological processes control mercury reduction during photosynthesis and fermentation

2020 ◽  
Author(s):  
Daniel S. Grégoire ◽  
Sarah E. Janssen ◽  
Noémie C. Lavoie ◽  
Michael T. Tate ◽  
Alexandre J. Poulain
Keyword(s):  
Food Webs ◽  
Isotope Fractionation ◽  
Atomic Level ◽  
Isotope Enrichment ◽  
Anoxygenic Photosynthesis ◽  
Physiological Processes ◽  
Mercury Uptake ◽  
Mercury Reduction ◽  
Mass Dependent Fractionation ◽  
Heliobacterium Modesticaldum

ABSTRACTMercury (Hg) is a global pollutant and potent neurotoxin that bioaccumulates in food webs as monomethylmercury (MeHg). The production of MeHg is driven by anaerobic and Hg redox cycling pathways such as Hg reduction, which control the availability of Hg to methylators. Anaerobes play an important role in Hg reduction in methylation hotspots, yet their contributions remain underappreciated due to how challenging these pathways are to study in the absence of dedicated genetic targets and low levels of Hg0 in anoxic environments. In this study we used Hg stable isotope fractionation to explore Hg reduction during anoxygenic photosynthesis and fermentation in the model anaerobe Heliobacterium modesticaldum Ice1. We show that cells preferentially reduce lighter Hg isotopes in both metabolisms leading to mass-dependent fractionation, but mass-independent fractionation commonly induced by UV-visible light is absent. We show that isotope fractionation is affected by the interplay between pathways controlling Hg recruitment, accessibility, and availability alongside metabolic redox reactions. The combined contributions of these processes lead to isotopic enrichment during anoxygenic photosynthesis that is in between the values reported for anaerobic respiratory microbial Hg reduction and abiotic photoreduction. Isotope enrichment during fermentation is closer to what has been observed in aerobic bacteria that reduce Hg through dedicated detoxification pathways. These results demonstrate that common controls exist at the atomic level for Hg reduction during photosynthesis and fermentation in H. modesticaldum. Our work suggests that similar controls likely underpin diverse microbe-mediated Hg transformations that affect Hg’s fate in oxic and anoxic habitats.IMPORTANCEAnaerobic and photosynthetic bacteria that reduce mercury affect mercury delivery to microbes in methylation sites that drive bioaccumulation in food webs. Anaerobic mercury reduction pathways remain underappreciated in the current view of the global mercury cycle because they are challenging to study, bearing no dedicated genetic targets to establish physiological mechanisms. In this study we used stable isotopes to show that common physiological processes control mercury reduction during photosynthesis and fermentation in the model anaerobe Heliobacterium modesticaldum Ice1. The sensitivity of isotope analyses highlighted the subtle contribution of mercury uptake towards the isotope signature associated with anaerobic mercury reduction. When considered alongside the isotope signatures associated with microbial pathways for which genetic determinants have been identified, our findings underscore the narrow range of isotope enrichment that is characteristic of microbial mercury transformations. This suggests that there exist common atomic-level controls for biological mercury transformations across a broad range of geochemical conditions.

scholarly journals Stable isotope fractionation reveals similar atomic level controls during aerobic and anaerobic microbial Hg transformation pathways

2021 ◽  
Author(s):  
Daniel S. Grégoire ◽  
Sarah E. Janssen ◽  
Noémie C. Lavoie ◽  
Michael T. Tate ◽  
Alexandre J. Poulain
Keyword(s):  
Stable Isotope ◽  
Food Webs ◽  
Isotope Fractionation ◽  
Atomic Level ◽  
Isotope Enrichment ◽  
Anoxygenic Photosynthesis ◽  
Physiological Processes ◽  
Stable Isotope Fractionation ◽  
Mercury Reduction ◽  
Heliobacterium Modesticaldum

Mercury (Hg) is a global pollutant and potent neurotoxin that bioaccumulates in food webs as monomethylmercury (MeHg). The production of MeHg is driven by anaerobic and Hg redox cycling pathways such as Hg reduction, which control the availability of Hg to methylators. Anaerobes play an important role in Hg reduction in methylation hotspots, yet their contributions remain underappreciated due to how challenging these pathways are to study in the absence of dedicated genetic targets and low levels of Hg 0 in anoxic environments. In this study we used Hg stable isotope fractionation to explore Hg reduction during anoxygenic photosynthesis and fermentation in the model anaerobe Heliobacterium modesticaldum Ice1. We show that cells preferentially reduce lighter Hg isotopes in both metabolisms leading to mass-dependent fractionation, but mass-independent fractionation commonly induced by UV-visible light is absent. Due to variability associated with replicated experiments, we could not discern whether dedicated physiological processes drive Hg reduction during photosynthesis and fermentation. However, we demonstrate that fractionation is affected by the interplay between pathways controlling Hg recruitment, accessibility, and availability alongside metabolic redox reactions. The combined contributions of these processes lead to isotopic enrichment during anoxygenic photosynthesis that is in between the values reported for anaerobic respiratory microbial Hg reduction and abiotic photoreduction. Isotope enrichment during fermentation is closer to what has been observed in aerobic bacteria that reduce Hg through dedicated detoxification pathways. Our work suggests that similar controls likely underpin diverse microbe-mediated Hg transformations that affect Hg’s fate in oxic and anoxic habitats. IMPORTANCE Anaerobic and photosynthetic bacteria that reduce mercury affect mercury delivery to microbes in methylation sites that drive bioaccumulation in food webs. Anaerobic mercury reduction pathways remain underappreciated in the current view of the global mercury cycle because they are challenging to study, bearing no dedicated genetic targets to establish physiological mechanisms. In this study we used stable isotopes to characterize the physiological processes that control mercury reduction during photosynthesis and fermentation in the model anaerobe Heliobacterium modesticaldum Ice1. The sensitivity of isotope analyses highlighted the subtle contribution of mercury uptake towards the isotope signature associated with anaerobic mercury reduction. When considered alongside the isotope signatures associated with microbial pathways for which genetic determinants have been identified, our findings underscore the narrow range of isotope enrichment that is characteristic of microbial mercury transformations. This suggests that there exist common atomic-level controls for biological mercury transformations across a broad range of geochemical conditions.

Variations in Stable Isotope Fractionation of Hg in Food Webs of Arctic Lakes

2009 ◽  
Vol 43 (24) ◽  
pp. 9148-9154 ◽  
Author(s):  
Nikolaus Gantner ◽  
Holger Hintelmann ◽  
Wang Zheng ◽  
Derek C. Muir
Keyword(s):  
Stable Isotope ◽  
Food Webs ◽  
Isotope Fractionation ◽  
Arctic Lakes ◽  
Stable Isotope Fractionation

Mercury isotope fractionation during the exchange of Hg between the atmosphere and land surfaces: implications for atmospheric Hg cycles

2020 ◽  
Author(s):  
Wei Zhu ◽  
Xuewu Fu ◽  
Hui Zhang ◽  
Chen Liu ◽  
Ben Yu ◽  
...  
Keyword(s):  
Land Surface ◽  
Isotope Fractionation ◽  
Agricultural Soils ◽  
Mining Area ◽  
Balance Model ◽  
Flux Chamber ◽  
Biogeochemical Models ◽  
Mass Dependent Fractionation ◽  
Hg Mining ◽  
Soil Hg

<p>Mercury (Hg) is a neurotoxic pollutant distributed globally via atmospheric transportation of elemental Hg (Hg(0)). Both anthropogenic and natural processes emit Hg to the atmosphere, where the later contributes up to approximately two thirds of the total emissions. Hg(II) in the Earth’s surface can be reduced chemically and biologically, resulted subsequent re-emission of Hg(0) back to the atmosphere. The Hg(0) exhibits bi-directional exchange (i.e., deposition and/or emission) between the land surface and atmosphere. Soil is the largest terrestrial Hg reservoir and its interaction with the atmosphere influences the atmospheric Hg cycling largely. Hg(0) emission from the terrestrial surfaces soil has been postulated to carry a negative MDF and positive MIF in the global Hg biogeochemical models. However, to date, no experimental evidence support that the complex terrestrial soil Hg(0) emission in accordance with this hypothetical simplification.</p><p>We coupled the <em>in-situ</em> Hg(0) dynamic flux chamber measurement and stable Hg isotope analysis to report a first dataset on the Hg isotope fractionation during the exchange of Hg(0) between the atmosphere and  8 soils and 1 cinnabar surfaces. The effect of air-soil/cinnabar exchange shifted Hg(0) concentrations in the flux chamber [i.e., (Hg(0)<sub>chamber</sub>-Hg(0)<sub>ambient</sub>)/Hg(0)<sub>chamber</sub>] by a factor of -0.29 – 0.90, corresponding to Hg(0) exchange fluxes ranging from -773 – 14457 ng m<sup>-2</sup> h<sup>-1</sup>. Our results showed that the exchange of Hg(0) between the atmosphere and soil/cinnabar could lead to an enrichment of both light and heavy isotopes (δ<sup>202</sup>Hg signatures) in Hg(0), as well as depletion or enrichment of odd isotopes (Δ<sup>199</sup>Hg signatures). This highlighted that multiple processes controlled the land-atmosphere exchange of Hg(0) and affected Hg isotope fractionation. Using a conservative isotope mass balance model, we found urban soils Hg(0) emission exhibited large variations in both δ<sup>202</sup>Hg (-3.04 to -0.34‰) and Δ<sup>199</sup>Hg (-0.60 to 0.38‰), which might be controlled by the Hg isotopic signatures in soils and environmental factors. The isotope signatures of Hg(0) emitted from agricultural background soils (δ<sup>202</sup>Hg = -1.31 ± 1.09‰, Δ<sup>199</sup>Hg = -0.26 ± 0.16‰, 1σ, n=15) and Hg-enriched agricultural soils in Hg mining area (δ<sup>202</sup>Hg = 0.51 ± 1.09‰, Δ<sup>199</sup>Hg = -0.10 ± 0.11‰, 1σ, n=12) exhibited contrasting mass dependent fractionation (MDF). Photo-reduction of soil Hg(II) coordinated to sulfurless ligands likely dominated the MIF of Hg isotope during the exchange of Hg between the atmosphere and  both urban and agricultural soils. While the positive shift of δ<sup>202</sup>Hg in mining area suggested that other processes including sorption and oxidation were also important in controlling MDF of Hg isotope during air/soil exchange. In a line with Hg-enriched agricultural soils, the forest soil emitted Hg(0) in Hg mining area enriched in heavy isotopes relative to the soil but depleted in odd isotopes. Hg(0) emission from cinnabar ore waste exhibited significant negative δ<sup>202</sup>Hg (-2.21 to -1.67‰) but positive Δ<sup>199</sup>Hg (0.17 to 0.38‰). Our results demonstrate complex Hg isotope fractionation during air-soil/cinnabar Hg(0) exchange resulted contrasting enrichment or depletion effects on the atmospheric Hg isotope compositions, thus have important implications for understanding the atmospheric Hg isotope signatures and modeling the global Hg cycling.</p>

scholarly journals Plant-ants feed their host plant, but above all a fungal symbiont to recycle nitrogen

2010 ◽  
Vol 278 (1710) ◽  
pp. 1419-1426 ◽  
Author(s):  
Emmanuel Defossez ◽  
Champlain Djiéto-Lordon ◽  
Doyle McKey ◽  
Marc-André Selosse ◽  
Rumsaïs Blatrix
Keyword(s):  
Food Webs ◽  
Host Plant ◽  
Isotope Enrichment ◽  
Plant Surface ◽  
Fungal Symbiont ◽  
Fungal Association ◽  
Simple Molecules ◽  
Different Parts ◽  
Fungal Associate

In ant–plant symbioses, plants provide symbiotic ants with food and specialized nesting cavities (called domatia). In many ant–plant symbioses, a fungal patch grows within each domatium. The symbiotic nature of the fungal association has been shown in the ant-plant Leonardoxa africana and its protective mutualist ant Petalomyrmex phylax . To decipher trophic fluxes among the three partners, food enriched in 13 C and 15 N was given to the ants and tracked in the different parts of the symbiosis up to 660 days later. The plant received a small, but significant, amount of nitrogen from the ants. However, the ants fed more intensively the fungus. The pattern of isotope enrichment in the system indicated an ant behaviour that functions specifically to feed the fungus. After 660 days, the introduced nitrogen was still present in the system and homogeneously distributed among ant, plant and fungal compartments, indicating efficient recycling within the symbiosis. Another experiment showed that the plant surface absorbed nutrients (in the form of simple molecules) whether or not it is coated by fungus. Our study provides arguments for a mutualistic status of the fungal associate and a framework for investigating the previously unsuspected complexity of food webs in ant–plant mutualisms.

scholarly journals Most natural-forming calcites precipitate at isotopic equilibrium

2021 ◽  
Author(s):  
Yuan jie
Keyword(s):  
Oxygen Isotope ◽  
Thermodynamic Equilibrium ◽  
Isotope Fractionation ◽  
Atomic Level ◽  
Quantum Mechanical ◽  
Isotopic Equilibrium ◽  
Oxygen Isotope Fractionation ◽  
Carbon And Oxygen Isotope ◽  
Devils Hole ◽  
Slow Growing

Abstract Based on thermodynamic equilibrium isotope fractionation theory, this letter reasonably understands the clumping 13C-18O (Δ47 ), as well as carbon and oxygen isotope fractionation in calcites with extremely slow-growing rates from Devils Hole and Laghetto Basso (Corchia Cave) at atomic level with solid physical precipitation models and quantum-mechanical backgrounds. It is found that most calcites in nature precipitate in at equilibrium.

Pathways of N and C uptake and transfer in stream food webs: an isotope enrichment experiment

2005 ◽  
Vol 24 (4) ◽  
pp. 955-975 ◽  
Author(s):  
Stephanie M. Parkyn ◽  
John M. Quinn ◽  
Tim J. Cox ◽  
Niall Broekhuizen
Keyword(s):  
Food Webs ◽  
Isotope Enrichment ◽  
Stream Food Webs

scholarly journals Inorganic Mercury and Methyl-Mercury Uptake and Effects in the Aquatic Plant Elodea nuttallii: A Review of Multi-Omic Data in the Field and in Controlled Conditions

2020 ◽  
Vol 10 (5) ◽  
pp. 1817
Author(s):  
Claudia Cosio
Keyword(s):  
Food Webs ◽  
Cell Walls ◽  
Inorganic Mercury ◽  
Elodea Nuttallii ◽  
Cellular Toxicity ◽  
Individual Level ◽  
Mercury Uptake ◽  
The Individual ◽  
Methyl Hg ◽  
Toxicity Pathways

(1) Background: Mercury is a threat for the aquatic environment. Nonetheless, the entrance of Hg into food webs is not fully understood. Macrophytes are both central for Hg entry in food webs and are seen as good candidates for biomonitoring and bioremediation; (2) Methods: We review the knowledge gained on the uptake and effects of inorganic Hg (IHg) and methyl-Hg (MMHg) in the macrophyte Elodea nuttallii found in temperate freshwaters; (3) Results: E. nuttallii bioaccumulates IHg and MMHg, but IHg shows a higher affinity to cell walls. At the individual level, IHg reduced chlorophyll, while MMHg increased anthocyanin. Transcriptomics and metabolomics in shoots revealed that MMHg regulated a higher number of genes than IHg. Proteomics and metabolomics in cytosol revealed that IHg had more effect than MMHg; (4) Conclusions: MMHg and IHg show different cellular toxicity pathways. MMHg’s main impact appears on the non-soluble compartment, while IHg’s main impact happens on the soluble compartment. This is congruent with the higher affinity of IHg with dissolved OM (DOM) or cell walls. E. nuttallii is promising for biomonitoring, as its uptake and molecular responses reflect exposure to IHg and MMHg. More generally, multi-omics approaches identify cellular toxicity pathways and the early impact of sublethal pollution.

Stable Ca and Sr isotopes support volcanically triggered biocalcification crisis during Oceanic Anoxic Event 1a

Geology ◽  
2020 ◽  
Author(s):  
Jiuyuan Wang ◽  
Andrew D. Jacobson ◽  
Bradley B. Sageman ◽  
Matthew T. Hurtgen
Keyword(s):  
Isotope Fractionation ◽  
Variable Mass ◽  
Large Igneous Province ◽  
Emergent Properties ◽  
Ionization Mass ◽  
Sr Isotope ◽  
Ocean Drilling Program ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Mass Dependent Fractionation

Large igneous province (LIP) eruptions are hypothesized to trigger biocalcification crises. The Aptian nannoconid crisis, which correlates with emplacement of the Ontong Java Plateau and Oceanic Anoxic Event 1a (OAE 1a, ca. 120 Ma), represents one such example. The Ca isotope (δ44/40Ca) system offers potential to detect biocalcification fluctuations in the rock record because Ca isotope fractionation is sensitive to precipitation rate. However, other primary and secondary processes, such as input-output flux perturbations and early diagenesis, can produce similar signals. Here, we exploit emergent properties of the stable Sr isotope (δ88/86Sr) system to resolve the origin of δ44/40Ca variability during OAE 1a. This study reports high-precision thermal ionization mass spectrometry (TIMS) δ44/40Ca, δ88/86Sr, and 87Sr/86Sr records for Hole 866A of Ocean Drilling Program Leg 143 drilled in Resolution Guyot, mid-Pacific Ocean. The samples span ~27 m.y. from the Barremian (ca. 127 Ma) to the Albian (ca. 100 Ma). The δ44/40Ca and δ88/86Sr secular trends differ from the 87Sr/86Sr record but mimic each other. δ44/40Ca and [Sr], as well as δ44/40Ca and δ88/86Sr, strongly correlate and yield slopes predicted for kinetic control, which demonstrates that variable mass-dependent fractionation rather than end-member mixing dominated the isotopic relationship between carbonates and seawater. Positive δ44/40Ca and δ88/86Sr shifts that begin before OAE 1a and peak within the interval are consistent with reduced precipitation rates. All results combined point to a cascade of effects on rate-dependent Ca and Sr isotope fractionation, which derive from the dynamic interplay between LIP eruptions and biocalcification feedbacks.

Mercury isotope fractionation during dark abiotic reduction of Hg(II) by dissolved and surface-bound Fe(II) species

2020 ◽  
Author(s):  
Lorenz Schwab ◽  
David S. McLagan ◽  
Stephan M. Kraemer ◽  
Harald Biester ◽  
Jan G. Wiederhold
Keyword(s):  
Stable Isotope ◽  
Isotope Fractionation ◽  
Batch Reactor ◽  
Reducing Agent ◽  
Low Flow ◽  
Redox Transformations ◽  
Stable Isotope Fractionation ◽  
Abiotic Reduction ◽  
Mass Dependent Fractionation ◽  
Fractionation Factors

<p>For many metals, including mercury (Hg), the transformation between different redox states is an important process for stable isotope fractionation. Identifying fractionation factors for specific Hg redox transformations therefore enables stable Hg isotope techniques to be used as a tool to trace biogeochemical processes and improve our understanding of the transport and fate of Hg in the environment. Previous studies demonstrated that reduced iron (Fe) species and Fe<sup>(II)</sup>-bearing minerals such as magnetite, green rust, siderite or vivianite are capable of reducing Hg<sup>(II)</sup> to Hg<sup>(I)</sup> and Hg<sup>(0)</sup>. These processes may be important in environments with low organic matter concentration and changing redox conditions such as groundwater aquifers or temporarily flooded soils.</p><p>In this study homogeneous and heterogeneous redox reactions of Hg<sup>(II)</sup> with dissolved Fe<sup>(II)</sup> and Fe<sup>(II)</sup>-bearing minerals are investigated in batch experiments under oxygen-free conditions in a glove bag. Mercury stock solutions prepared from NIST-3133 in a glass batch reactor are continuously stirred to minimize local reducing zones and wrapped in aluminum foil to prevent photoreduction. The reducing agents are added stepwise to reduce fractions of Hg until complete reduction is achieved. The produced Hg<sup>(0)</sup> is continuously purged into an oxidizing trap solution (40% inverse aqua regia with BrCl) with nitrogen gas at a low flow rate. After each reduction step solution aliquots are taken from the reactor and the trap is exchanged. Total Hg concentrations in reactor and trap samples are then measured with CV-AAS/AFS and isotopic compositions determined with CV-MC-ICP-MS.</p><p>Initially, different amounts of SnCl<sub>2</sub> were used as reducing agent to test the experimental setup similar to [1]. For this experiment we observed consistent isotopic trends which could be described by a Rayleigh model fit with mass dependent fractionation (ε<sup>202</sup>Hg = -­2.75 ± 0.07‰) as well as mass independent fractionation of odd-mass Hg isotopes (Ε<sup>199</sup>Hg = ­0.32 ± 0.04‰). The slope of the linear regression of Δ<sup>199</sup>Hg/Δ<sup>201</sup>Hg of 1.52 ± 0.1 indicates that the MIF was likely caused by the nuclear volume effect. In subsequent experiments different amounts of a Fe<sup>(II)</sup> stock solution prepared from Fe<sup>(II)</sup>Cl<sub>2</sub> are used as reducing agent. Additionally, experiments are carried out with Fe<sup>(II)</sup>-bearing minerals and Fe<sup>(II)</sup> adsorbed to mineral surfaces.</p><p>The results produced from this study will be very useful for the interpretation of field data from temporarily anoxic groundwater bodies at contaminated sites (e.g. [2]). The insights from the experiments will further contribute to the understanding of the interplay between Hg and Fe biogeochemical cycles and redox transformations. Most importantly, it will add much needed fractionation factors to the toolbox of Hg stable isotope fractionation as a tracer for biogeochemical transformations.</p><p>[1] Zheng, W., Hintelmann, H. (2010) Nuclear field shift effect in isotope fractionation of mercury during abiotic reduction in the absence of light. J. Phys. Chem. A, 114(12), 4238–4245.</p><p>[2] Richard, J.-H., Bischoff, C., Ahrens, C.G.M., Biester, H. (2016) Mercury(II) reduction and co-precipitation of metallic mercury on hydrous ferric oxide in contaminated groundwater. Sci. Tot. Environ. 539, 36–44.</p>

Zinc Isotope Fractionation during Sorption onto Al Oxides: Atomic Level Understanding from EXAFS

2018 ◽  
Vol 52 (16) ◽  
pp. 9087-9096 ◽  
Author(s):  
Wenxian Gou ◽  
Wei Li ◽  
Junfeng Ji ◽  
Weiqiang Li
Keyword(s):  
Isotope Fractionation ◽  
Atomic Level ◽  
Zinc Isotope
Sign in / Sign up

Export Citation Format

Share Document