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Khodavysi M, Kheiripour N, Ghasemi H, Soleimani-Asl S, Jouzdani AF, Sabahi M, Ganji Z, Azizi Z, Ranjbar A. How can nanomicelle-curcumin modulate aluminum phosphide-induced neurotoxicity?: Role of SIRT1/FOXO3 signaling pathway. AIMS Neurosci 2023; 10:56-74. [PMID: 37077959 PMCID: PMC10106336 DOI: 10.3934/neuroscience.2023005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 03/22/2023] [Accepted: 03/27/2023] [Indexed: 04/21/2023] Open
Abstract
Aluminum phosphide (ALP) is among the most significant causes of brain toxicity and death in many countries. Curcumin (CUR), a major turmeric component, is a potent protective agent against many diseases, including brain toxicity. This study aimed to examine the probable protection potential of nanomicelle curcumin (nanomicelle-CUR) and its underlying mechanism in a rat model of ALP-induced brain toxicity. A total of 36 Wistar rats were randomly divided into six groups (n = 6) and exposed to ALP (2 mg/kg/day, orally) + CUR or nanomicelle-CUR (100 mg/kg/day, orally) for 7 days. Then, they were anesthetized, and brain tissue samples were dissected to evaluate histopathological alterations, oxidative stress biomarkers, gene expression of SIRT1, FOXO1a, FOXO3a, CAT and GPX in brain tissue via hematoxylin and eosin (H&E) staining, biochemical and enzyme-linked immunosorbent assay (ELISA) methods and Real-Time PCR analysis. CUR and nanomicelle-CUR caused significant improvement in ALP-induced brain damage by reducing the MDA levels and induction of antioxidant capacity (TTG, TAC and SOD levels) and antioxidant enzymes (CAT, GPX), modulation of histopathological changes and up-regulation of gene expression of SIRT1 in brain tissue. It was concluded that nanomicelle-CUR treatment ameliorated the harmful effects of ALP-induced brain toxicity by reducing oxidative stress. Therefore, it could be considered a suitable therapeutic choice for ALP poisoning.
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Affiliation(s)
- Milad Khodavysi
- Department of Pharmacology and Toxicology, School of Pharmacy, Medicinal Plants and Natural Products Research Center, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Nejat Kheiripour
- Research Center for Biochemistry and Nutrition in Metabolic Diseases, Kashan University of Medical Sciences, Kashan, Iran
| | - Hassan Ghasemi
- Department of Clinical Biochemistry, Abadan University of Medical Sciences, Abadan, Iran
| | - Sara Soleimani-Asl
- Department of Anatomical Sciences, Faculty of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Ali Fathi Jouzdani
- Neuroscience and Artificial Intelligence Research Group (NAIRG), Student Research Committee, Hamadan University of Medical Sciences, Hamadan, Iran
- USERN office, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Mohammadmahdi Sabahi
- Department of Neurosurgery, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
| | - Zahra Ganji
- USERN office, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Zahra Azizi
- Neuroscience and Artificial Intelligence Research Group (NAIRG), Student Research Committee, Hamadan University of Medical Sciences, Hamadan, Iran
- USERN office, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Akram Ranjbar
- Department of Pharmacology and Toxicology, School of Pharmacy, Medicinal Plants and Natural Products Research Center, Hamadan University of Medical Sciences, Hamadan, Iran
- * Correspondence: E-mail: ; Tel: +988138381590
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Deng N, Zuo X, Stack AG, Lee SS, Zhou Z, Weber J, Hu Y. Selenite and Selenate Sequestration during Coprecipitation with Barite: Insights from Mineralization Processes of Adsorption, Nucleation, and Growth. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:15518-15527. [PMID: 36322394 DOI: 10.1021/acs.est.2c03292] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Coprecipitation of selenium oxyanions with barite is a facile way to sequester Se in the environments. However, the chemical composition of Se-barite coprecipitates usually deviates from that predicted from thermodynamic calculations. This discrepancy was resolved by considering variations in nucleation and growth rates controlled by ion-mineral interactions, solubility, and interfacial energy. For homogeneous precipitation, ∼10% of sulfate, higher than thermodynamic predictions (<0.3%), was substituted by Se(IV) or Se(VI) oxyanion, which was attributed to adsorption-induced entrapment during crystal growth. For heterogeneous precipitation, thiol- and carboxylic-based organic films, utilized as model interfaces to mimic the natural organic-abundant environments, further enhanced the sequestration of Se(VI) oxyanions (up to 41-92%) with barite. Such enhancement was kinetically driven by increased nucleation rates of selenate-rich barite having a lower interfacial energy than pure barite. In contrast, only small amounts of Se(IV) oxyanions (∼1%) were detected in heterogeneous coprecipitates mainly due to a lower saturation index of BaSeO3 and deprotonation degree of Se(IV) oxyanion at pH 5.6. These roles of nanoscale mineralization mechanisms observed during composition selection of Se-barite could mark important steps toward the remediation of contaminants through coprecipitation.
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Affiliation(s)
- Ning Deng
- Department of Civil and Environmental Engineering, University of Houston, Houston, Texas77004, United States
- School of Environmental and Chemical Engineering, Shanghai University, Shanghai200444, China
| | - Xiaobing Zuo
- X-ray Science Division, Argonne National Laboratory, Lemont, Illinois60439, United States
| | - Andrew G Stack
- Chemical Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Sang Soo Lee
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois60439, United States
| | - Zehao Zhou
- The Key Laboratory of Water and Sediment Sciences, College of Environmental Sciences and Engineering, State Environmental Protection Key Laboratory of All Material Fluxes in River Ecosystems, Peking University, Beijing100871, China
| | - Juliane Weber
- Chemical Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Yandi Hu
- Department of Civil and Environmental Engineering, University of Houston, Houston, Texas77004, United States
- The Key Laboratory of Water and Sediment Sciences, College of Environmental Sciences and Engineering, State Environmental Protection Key Laboratory of All Material Fluxes in River Ecosystems, Peking University, Beijing100871, China
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Yang P, Jiang T, Cong Z, Liu G, Guo Y, Liu Y, Shi J, Hu L, Yin Y, Cai Y, Jiang G. Loss and Increase of the Electron Exchange Capacity of Natural Organic Matter during Its Reduction and Reoxidation: The Role of Quinone and Nonquinone Moieties. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:6744-6753. [PMID: 35522821 DOI: 10.1021/acs.est.1c08927] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Redox-active quinone and nonquinone moieties represent the electron exchange capacity (EEC) of natural organic matter (NOM), playing an important role in the electron transfer link of microbes and transformation of contaminants/metal minerals. However, the corresponding transformation of quinone/phenol and their respective influence on the EECs during reduction and reoxidation remain poorly characterized. Besides, it is still controversial whether nonquinones donate or accept electrons. Herein, we demonstrated that reoxidation of NOM after reduction can form new phenolic/quinone moieties, thus increasing the EEC. The assessment for the EEC, including the electron-donating capacity (EDC) and electron-accepting capacity (EAC), of nonquinones reflects the contribution of sulfur-containing moieties with considerable EDCs and EACs. In contrast, nitrogen-containing moieties donate negligible electrons even at Eh = +0.73 V. The contributions of both thiol and amine moieties to the EEC are greatly affected by adjacent functional groups. Meanwhile, aldehydes/ketones did not display an EAC during the electron transfer process of NOM. Furthermore, substantially increased EDC at Eh from +0.61 to +0.73 V could not be fully explained using thiol and phenolic moieties, suggesting the contribution of unknown moieties with high oxidation potential. The overall findings suggest that the roles of new quinones/phenol (derived from the addition of oxygen to condensed aromatic/lignin-like components) during redox dynamic cycling and thiol species should be considered in assessing the electron transfer processes of NOM.
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Affiliation(s)
- Peijie Yang
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Tao Jiang
- Interdisciplinary Research Centre for Agriculture Green Development in Yangtze River Basin, College of Resources and Environment, Southwest University, Chongqing 400716, China
| | - Zhiyuan Cong
- Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Guangliang Liu
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Yingying Guo
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Yanwei Liu
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Jianbo Shi
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ligang Hu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yongguang Yin
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- School of Environment, Hangzhou Institute for Advanced Study, UCAS, Hangzhou 310024, China
| | - Yong Cai
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Guibin Jiang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of Chinese Academy of Sciences, Beijing 100049, China
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Worms IAM, Kavanagh K, Moulin E, Regier N, Slaveykova VI. Asymmetrical Flow Field-Flow Fractionation Methods for Quantitative Determination and Size Characterization of Thiols and for Mercury Size Speciation Analysis in Organic Matter-Rich Natural Waters. Front Chem 2022; 10:800696. [PMID: 35252112 PMCID: PMC8888841 DOI: 10.3389/fchem.2022.800696] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2021] [Accepted: 01/05/2022] [Indexed: 12/13/2022] Open
Abstract
Asymmetrical flow field-flow fractionation (AF4) efficiently separates various macromolecules and nano-components of natural waters according to their hydrodynamic sizes. The online coupling of AF4 with fluorescence (Fluo) and UV absorbance (UV) detectors (FluoD and UVD, respectively) and inductively coupled plasma–mass spectrometry (ICP-MS) provides multidimensional information. This makes it a powerful tool to characterize and quantify the size distributions of organic and inorganic nano-sized components and their interaction with trace metals. In this study, we developed a method combining thiol labeling by monobromo(trimethylammonio)bimane bromide (qBBr) with AF4–FluoD to determine the size distribution and the quantities of thiols in the macromolecular dissolved organic matter (DOM) present in highly colored DOM-rich water sampled from Shuya River and Lake Onego, Russia. We found that the qBBr-labeled components of DOM (qB-DOM) were of humic type, characterized by a low hydrodynamic size (dh < 2 nm), and have concentrations <0.3 μM. After enrichment with mercury, the complexes formed between the nano-sized components and Hg were analyzed using AF4–ICP-MS. The elution profile of Hg followed the distribution of the UV-absorbing components of DOM, characterized by slightly higher sizes than qB-DOM. Only a small proportion of Hg was associated with the larger-sized components containing Fe and Mn, probably inorganic oxides that were identified in most of the samples from river to lake. The size distribution of the Hg–DOM complexes was enlarged when the concentration of added Hg increased (from 10 to 100 nM). This was explained by the presence of small iron oxides, overlapping the size distribution of Hg–DOM, on which Hg bound to a small proportion. In addition, to provide information on the dispersion of macromolecular thiols in colored DOM-rich natural water, our study also illustrated the potential of AF4–FluoD–UVD–ICP-MS to trace or quantify dynamic changes while Hg binds to the natural nano-colloidal components of surface water.
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Mahlooji MA, Heshmati A, Kheiripour N, Ghasemi H, Asl SS, Solgi G, Ranjbar A, Hosseini A. Evaluation of Protective Effects of Curcumin and Nanocurcumin on Aluminium Phosphide‑Induced Subacute Lung Injury in Rats: Modulation of Oxidative Stress through SIRT1/FOXO3 Signalling Pathway. Drug Res (Stuttg) 2021; 72:100-108. [PMID: 34614532 DOI: 10.1055/a-1647-2418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
OBJECTIVE Aluminum phosphide (AlP) is widely used to protect stored food products and grains from pests and rodents. The availability of AlP, especially in Asian countries it has become a desirable factor to commit suicide. The phosphine produced from ALP is a very reactive radical and a respiratory inhibitor that causes oxidative damage. There is no dedicated antidote or effective drug to manage AlP-induced lung toxicity. The present study aims to evaluate and compare the protective effects of curcumin and nanocurcumin on ALP‑induced subacute lung injury and determine the underlying mechanism. METHODS Rats were exposed to AlP (2 mg/kg/day, orally)+curcumin or nanocurcumin (100 mg/kg/day, orally) for 7 days. Then rats were anesthetized and lung tissues were collected. Oxidative stress biomarkers, genes expression of antioxidant enzymes, participated genes in the SIRT1/FOXO3 pathway, and lung histopathology were assessed by biochemical and ELISA methods, Real-Time PCR analysis, and H&E staining. RESULTS Curcumin and nanocurcumin produced a remarkable improvement in AlP-induced lung damage through reduction of MDA, induction of antioxidant capacity (TAC, TTG) and antioxidant enzymes (CAT, GPx), modulation of histopathological changes, and up-regulation of genes expression of SIRT1, FOXO3, FOXO1 in lung tissue. CONCLUSION Nanocurcumin had a significantly more protective effect than curcumin to prevent AlP-induced lung injury via inhibition of oxidative stress. Nanocurcumin could be considered a suitable therapeutic choice for AlP poisoning.
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Affiliation(s)
- Mohammad Ali Mahlooji
- Department of Pharmacology and Toxicology, School of Pharmacy, Medicinal Plants and Natural Products Research Center, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Ali Heshmati
- Nutrition Health Research Center, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Nejat Kheiripour
- Research Center for Biochemistry and Nutrition in Metabolic Diseases, Kashan University of Medical Sciences, Kashan, Iran
| | - Hassan Ghasemi
- Department of Clinical Biochemistry, Abadan University of Medical Sciences, Abadan, Iran
| | - Sara Soleimani Asl
- Department of Anatomical Sciences, Faculty of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Ghasem Solgi
- Department of Immunology, Faculty of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Akram Ranjbar
- Department of Pharmacology and Toxicology, School of Pharmacy, Medicinal Plants and Natural Products Research Center, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Asieh Hosseini
- Razi Drug Research Center, Iran University of Medical Sciences, Tehran, Iran
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6
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Bland GD, Rao B, Reible D. Evaluating the transport of Hg(II) in the presence of natural organic matter through a diffusive gradient in a thin-film passive sampler. THE SCIENCE OF THE TOTAL ENVIRONMENT 2020; 749:141217. [PMID: 32827812 DOI: 10.1016/j.scitotenv.2020.141217] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2020] [Revised: 07/22/2020] [Accepted: 07/22/2020] [Indexed: 06/11/2023]
Abstract
The effects of a model natural organic matter (NOM) on the transport of Hg(II) into diffusive gradient in thin-film devices (DGTs) was evaluated in order to better understand their ability to measure colloidal Hg species in porewater. The presence of NOM significantly reduced the diffusivity of the Hg(II) species and the reduction was dependent upon NOM to Hg(II) ratio. This relationship was modeled by determining the Hg(II) partition coefficients (Kd) of size fractionated NOM obtained by ultrafiltration and estimating the Hg diffusivity through the DGT for the different NOM size fractions across a range of Hg-NOM ratios. The estimated diffusivities were consistent with experimental observations of uptake into the DGT. Overall, this study indicated that Hg(II) associated with NOM passes into a DGT, however the transport is slowed in accordance with the diffusivity of the NOM to which the Hg(II) is associated. Thus, the Hg-NOM association and complex diffusivities need to be considered when relating DGT uptake to Hg porewater concentration. The results also suggest that Hg(II) associated with colloidal or larger particles of negligible diffusivity are unlikely to contribute significantly to DGT measurements.
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Affiliation(s)
- Garret D Bland
- Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States; Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Lubbock, TX 79409, United States
| | - Balaji Rao
- Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Lubbock, TX 79409, United States
| | - Danny Reible
- Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Lubbock, TX 79409, United States.
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7
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Xu Y, Wang K, Zhou Q, Zhang L, Qian G. Effects of humus on the mobility of arsenic in tailing soil and the thiol-modification of humus. CHEMOSPHERE 2020; 259:127403. [PMID: 32603963 DOI: 10.1016/j.chemosphere.2020.127403] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 06/09/2020] [Accepted: 06/11/2020] [Indexed: 06/11/2023]
Abstract
The ability of thiol-modified humic acids (HAs) to release arsenic in tailings soil after being modified with different sulfur-containing reagents were significantly improved. The structure and physicochemical properties of humic acid (HA) before and after thiol-modification were characterized. The 3-MPTS-HA treated with 3-mercaptopropyltrimethoxysilane (3-MPTS) effectively improved the mobility of arsenic, and its reducing ability was increased from 2 mmol g-1 to 3.54 mmol g-1. The S content of humic acids were also significantly increased after treatment with sulfur-containing reagents, in which the oxygen-containing functional group (e.g., C = O, C-O) on the surface of HA may be the active sites for binding with sulfur-containing reagents. It was found in the XPS spectrum that because the thiol group is easily oxidized, there are many S forms in thiol-modified HA. The -SH content in Na2S·9H2O-HA, l (+)-Cysteine-HA (Cys-HA), thioglycolic acid (TGA-HA) and 3-MPTS-HA was determined by fluorescence method to be 13.9, 78.45, 90.34, and 192.29 μmol g-1, respectively. The study demonstrated that surface thiol modification can increase the abundance of thiol in HA and enhance reactivity, which will further promote the application of HA in the treatment of heavy metal contaminated tailing soil.
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Affiliation(s)
- Yunfeng Xu
- School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China
| | - Kaili Wang
- School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China
| | - Qinghao Zhou
- School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China
| | - Liting Zhang
- School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China
| | - Guangren Qian
- School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China.
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8
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Huynh K, Liem-Nguyen V, Feng C, Lindberg R, Björn E. Quantification of total concentration of thiol functional groups in environmental samples by titration with monobromo(trimethylammonio)bimane and determination with tandem mass spectrometry. Talanta 2020; 218:121109. [PMID: 32797873 DOI: 10.1016/j.talanta.2020.121109] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 04/28/2020] [Accepted: 04/30/2020] [Indexed: 11/16/2022]
Abstract
Thiol compounds (R-SH) have many important biological functions and are principal controls of the speciation of several toxic metals in the environment. However, determining the concentration of thiols associated with environmental matrices is challenging due to the compounds' low abundance and interferences from non-thiol compounds for many available methods. Here a novel method has been developed and validated to quantify the total concentration of thiol functional groups in aqueous samples using derivatization with monobromo(trimethylammonio)bimane (qBBr) and quantification with tandem mass spectrometry. The thiol concentration was determined by titration of the sample with qBBr, which reacts selectively with thiols, and quantification of the residual qBBr. We systematically evaluated potential interferences from various organic compounds, inorganic ions (including sea water matrices), sulfide and mercury (Hg) species, and demonstrate that the method is highly sensitive, selective and robust. The limit of detection (LOD) for total thiols is in the nanomolar concentration range (~6 nM). The method performance was also demonstrated by determination of the total thiol concentration in different natural samples including boreal stream water (1.16 μM), wetland porewater (0.96 μM) and the Suwanee River natural organic matter (NOM) reference material SR101 N (7.9 μmol g-1). The developed method represents a combination of low LOD and high selectivity and robustness that is unsurpassed for total thiol concentration measurements.
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Affiliation(s)
- Khoa Huynh
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
| | - Van Liem-Nguyen
- Laboratory of Advanced Materials Chemistry, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam
| | - Caiyan Feng
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
| | - Richard Lindberg
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
| | - Erik Björn
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden.
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Song Y, Adediran GA, Jiang T, Hayama S, Björn E, Skyllberg U. Toward an Internally Consistent Model for Hg(II) Chemical Speciation Calculations in Bacterium-Natural Organic Matter-Low Molecular Mass Thiol Systems. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:8094-8103. [PMID: 32491838 PMCID: PMC7467648 DOI: 10.1021/acs.est.0c01751] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
To advance the scientific understanding of bacteria-driven mercury (Hg) transformation processes in natural environments, thermodynamics and kinetics of divalent mercury Hg(II) chemical speciation need to be understood. Based on Hg LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopic information, combined with competitive ligand exchange (CLE) experiments, we determined Hg(II) structures and thermodynamic constants for Hg(II) complexes formed with thiol functional groups in bacterial cell membranes of two extensively studied Hg(II) methylating bacteria: Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. The Hg EXAFS data suggest that 5% of the total number of membranethiol functionalities (Mem-RStot = 380 ± 50 μmol g-1 C) are situated closely enough to be involved in a 2-coordinated Hg(Mem-RS)2 structure in Geobacter. The remaining 95% of Mem-RSH is involved in mixed-ligation Hg(II)-complexes, combining either with low molecular mass (LMM) thiols like Cys, Hg(Cys)(Mem-RS), or with neighboring O/N membrane functionalities, Hg(Mem-RSRO). We report log K values for the formation of the structures Hg(Mem-RS)2, Hg(Cys)(Mem-RS), and Hg(Mem-RSRO) to be 39.1 ± 0.2, 38.1 ± 0.1, and 25.6 ± 0.1, respectively, for Geobacter and 39.2 ± 0.2, 38.2 ± 0.1, and 25.7 ± 0.1, respectively, for ND132. Combined with results obtained from previous studies using the same methodology to determine chemical speciation of Hg(II) in the presence of natural organic matter (NOM; Suwannee River DOM) and 15 LMM thiols, an internally consistent thermodynamic data set is created, which we recommend to be used in studies of Hg transformation processes in bacterium-NOM-LMM thiol systems.
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Affiliation(s)
- Yu Song
- Department
of Forest Ecology and Management, Swedish
University of Agricultural Science, SE-901 83 Umeå, Sweden
| | | | - Tao Jiang
- Department
of Forest Ecology and Management, Swedish
University of Agricultural Science, SE-901 83 Umeå, Sweden
| | - Shusaku Hayama
- Diamond
Light Source, Didcot, Oxfordshire OX11 0DE, United Kingdom
| | - Erik Björn
- Department
of Chemistry, Umeå University, SE-901 87 Umeå, Sweden
| | - Ulf Skyllberg
- Department
of Forest Ecology and Management, Swedish
University of Agricultural Science, SE-901 83 Umeå, Sweden
- . Phone: +46 (0)90-786 84 60
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10
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Martin LA, Simonucci C, Rad S, Benedetti MF. Effect of natural organic matter on thallium and silver speciation. J Environ Sci (China) 2020; 93:185-192. [PMID: 32446454 DOI: 10.1016/j.jes.2020.04.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Revised: 04/01/2020] [Accepted: 04/01/2020] [Indexed: 05/26/2023]
Abstract
Natural organic matter (NOM) is known to play an important role in the transport and binding of trace metal elements in aquatic and soil systems. Thallium is a pollutant for which the extent of the role played by NOM is poorly known. Consequently, this study investigates thallium(I) and its complexation to a purified humic substance as proxy for NOM. Experiments were performed with the Donnan Membrane Technique to separate, for the first time, the free Tl+ ion from its complexed form in the bulk solution. Various pH and concentrations were investigated at constant ionic strength and constant NOM proxy concentrations in solution. Experimental results were described with NICA-Donnan model. Thallium complexation was compared to silver complexation using literature data and using the same NICA-Donnan formalism. Parameters for these two cations (Tl+ and Ag+) are reported in this article, for the first time. Results display low thallium complexation to the NOM proxy while silver competes with divalent cations for the NOM binding sites. Calculated speciation for dissolved thallium highlights the dominance of free thallium (Tl+) in solution whereas Tl-NOM complexes contribute roughly 15% to total Tl(I) species in river and lake type waters. Similar results are obtained for soil solutions, Tl-bound to NOM < 30% of total, from UK soils with different land use and geochemistry.
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Affiliation(s)
- Loïc A Martin
- Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France; IRSN, PSE-ENV/SIRSE/LER-Nord, BP 17, 92262 Fontenay-aux-Roses Cedex, France; Catchment and Eco-Hydrology Research Group, Luxembourg Institute of Science and Technology, L-4422 Belvaux, Luxembourg
| | - Caroline Simonucci
- IRSN, PSE-ENV/SIRSE/LER-Nord, BP 17, 92262 Fontenay-aux-Roses Cedex, France
| | - Sétareh Rad
- BRGM, Unité de Géomicrobiologie et Monitoring Environnemental, 45060 Orléans Cedex 2, France
| | - Marc F Benedetti
- Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France.
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Mendonça MCP, de Jesus MB, van Gestel CAM. Protective effect of N-acetylcysteine on the toxicity of silver nanoparticles: Bioavailability and toxicokinetics in Enchytraeus crypticus. THE SCIENCE OF THE TOTAL ENVIRONMENT 2020; 715:136797. [PMID: 32014764 DOI: 10.1016/j.scitotenv.2020.136797] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Revised: 01/14/2020] [Accepted: 01/17/2020] [Indexed: 05/21/2023]
Abstract
We previously demonstrated that N-acetylcysteine (NAC) could reduce the toxicity of silver (Ag) materials (nanoparticles (NPs) and Ag nitrate) to the soil invertebrate Enchytraeus crypticus (Oligochaeta). It remains however, unclear whether the antitoxic mechanism of NAC was caused by NAC-Ag binding in the soil or inside the organisms. This study aimed at determining the bioavailability of Ag in the soil in a 21-day toxicity test as well as the Ag uptake and elimination kinetics in E. crypticus exposed to AgNPs in LUFA 2.2 standard soil amended with low (100 mg/kg dry soil) and high (600 mg/kg dry soil) NAC concentrations. The addition of NAC to the soil alleviated the toxicity of AgNPs by decreasing the internal Ag concentration of E. crypticus in a dose-dependent manner. Indeed, NAC reduced the binding of Ag to the soil, which probably was due to the formation of soluble but biologically unavailable Ag-cysteine complexes. The reduced Ag uptake in the enchytraeids was explained from an increased elimination at high NAC levels. These findings reinforce the view that metal complexing-compounds like NAC play a key role in the modulation of AgNP toxicity and bioavailability in terrestrial environments. Further, it may inform on the potential of NAC as a remediation solution for Ag or other metal-contaminated soils.
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Affiliation(s)
- Monique Culturato Padilha Mendonça
- Department of Biochemistry and Tissue Biology, Institute of Biology, University of Campinas, Campinas, São Paulo 13083-970, Brazil; Department of Ecological Science, Faculty of Science, Vrije Universiteit, Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands.
| | - Marcelo Bispo de Jesus
- Department of Biochemistry and Tissue Biology, Institute of Biology, University of Campinas, Campinas, São Paulo 13083-970, Brazil
| | - Cornelis A M van Gestel
- Department of Ecological Science, Faculty of Science, Vrije Universiteit, Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
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12
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Mangal V, Phung T, Guéguen C. An estimation of sulfur concentrations released by three algae (Chlorella vulgaris, Chlamydomonas reinhardtii, Scenedesmus obliquus) in response to variable growth photoperiods. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2020; 27:12491-12498. [PMID: 31997249 DOI: 10.1007/s11356-020-07812-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 01/21/2020] [Indexed: 06/10/2023]
Abstract
In this study, we estimated extracellular concentrations of algal-derived sulfur species in response to changing photoperiods. Cultures from three algal species (Chlorella vulgaris, Chlamydomonas reinhardtii, Scenedesmus obliquus) were subjected to five different light:dark cycles (12:12, 14:10, 16:8, 18:6, 20:4 h) for a period of 3 days. Sulfur compounds including total reactive thiol concentrations, electroactive reduced sulfur species (RSS), and thiol isomers were measured using qBBr fluorescence, differential pulse cathodic stripping voltammetry (DP-CSV), and high-resolution mass spectrometry (HRMS), respectively. Total reactive thiol concentrations were greater in Scenedesmus than in Chlamydomonas and Chlorella at low light regimes (i.e., 12:12 h) whereas Chlamydomonas produced more RSS than the other two species (p < 0.05) at any light regime. Scenedesmus was the only responsive species to produce maximal electroactive RSS, and HRMS equivalent thiol compounds under low light regime, congruent with previous studies. Principal component analysis revealed relationships between qBBr-equivalent thiol and GSH-equivalent RSS concentrations for Scenedesmus and Chlamydomonas (p < 0.05) suggesting that thiols were the dominant species in the pool of electroactive RSS for these two algal species. Overall, these results showed that the light growth conditions greatly influenced the production of S-rich compounds by algae, affecting the complexation of metals such as mercury and cadmium, especially during planktonic blooms.
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Affiliation(s)
- Vaughn Mangal
- Environmental and Life Sciences Graduate program, Trent University, Peterborough, ON, Canada
- Department of Chemistry, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Ta Phung
- Chemistry Department, Trent University, Peterborough, ON, Canada
| | - Céline Guéguen
- Department of Chemistry, Université de Sherbrooke, Sherbrooke, QC, Canada.
- Chemistry Department, Trent University, Peterborough, ON, Canada.
- School of the Environment, Trent University, Peterborough, ON, Canada.
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13
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Jia Y, Zhao T, Zhao N, Wei H, Zhang W, Qiu R. Effects of light irradiation on the complexes of cadmium and humic acids: The role of thiol groups. CHEMOSPHERE 2019; 225:174-181. [PMID: 30875500 DOI: 10.1016/j.chemosphere.2019.03.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2018] [Revised: 02/11/2019] [Accepted: 03/05/2019] [Indexed: 06/09/2023]
Abstract
In natural environments, humic substances (HS) play a key role in the control of Cd stability by forming Cd-HS complexes. In this study, we investigated the influence of the photo-irradiation on the Cd levels remaining in Leonardite humic acid (HA) standard solution after chemical precipitation. The kinetic experiment showed that after the irradiation of ultraviolet light, especially UVC, Cd-HA complexes become more stable. The coexisting Cd in the HA solution under light irradiation seemed to enhance the stability of Cd-HA complexes. Both Fourier transform infrared and X-ray photoelectron spectrometric spectra indicated an increase in the thiol amounts in the HA samples treated by light irradiation. Therefore, we developed a fluorescent method to quantify thiol groups in HA with N-(1-pyrenyl) maleimide (NPM). The HA samples were initially spiked with known amounts of glutathione, the reference containing thiol groups, and then was titrated with various amounts of NPM. The measured thiol amounts in the HA treated by UV were found to significantly increase, and the increment was almost equivalent to those of Cd level in HA solution after chemical precipitation. Therefore, it was concluded that the increased thiol groups in HA induced by ultraviolet irradiation resulted in the formation of more stable Cd-HA complexes in solution.
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Affiliation(s)
- Yanming Jia
- School of Environmental Science and Technology, Sun Yat-sen University, Guangzhou, 510275, China
| | - Tuokun Zhao
- School of Environmental Science and Technology, Sun Yat-sen University, Guangzhou, 510275, China
| | - Nan Zhao
- School of Environmental Science and Technology, Sun Yat-sen University, Guangzhou, 510275, China
| | - Hang Wei
- School of Environmental Science and Technology, Sun Yat-sen University, Guangzhou, 510275, China
| | - Weihua Zhang
- School of Environmental Science and Technology, Sun Yat-sen University, Guangzhou, 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution and Remediation Technology, Guangdong Provincial Engineering Research Center for Heavy Metal Contaminated Soil Remediation, Guangzhou, 510275, China; Shenzhen Research Institute, Sun Yat-sen University, Shenzhen, 518057, China.
| | - Rongliang Qiu
- School of Environmental Science and Technology, Sun Yat-sen University, Guangzhou, 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution and Remediation Technology, Guangdong Provincial Engineering Research Center for Heavy Metal Contaminated Soil Remediation, Guangzhou, 510275, China
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14
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Organic-mineral interfacial chemistry drives heterogeneous nucleation of Sr-rich (Ba x , Sr 1-x )SO 4 from undersaturated solution. Proc Natl Acad Sci U S A 2019; 116:13221-13226. [PMID: 31113880 DOI: 10.1073/pnas.1821065116] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Sr-bearing marine barite [(Ba x , Sr1-x )SO4] cycling has been widely used to reconstruct geochemical evolutions of paleoenvironments. However, an understanding of barite precipitation in the ocean, which is globally undersaturated with respect to barite, is missing. Moreover, the reason for the occurrence of higher Sr content in marine barites than expected for classical crystal growth processes remains unknown. Field data analyses suggested that organic molecules may regulate the formation and composition of marine barites; however, the specific organic-mineral interactions are unclear. Using in situ grazing incidence small-angle X-ray scattering (GISAXS), size and total volume evolutions of barite precipitates on organic films were characterized. The results show that barite forms on organic films from undersaturated solutions. Moreover, from a single supersaturated solution with respect to barite, Sr-rich barite nanoparticles formed on organics, while micrometer-size Sr-poor barites formed in bulk solutions. Ion adsorption experiments showed that organic films can enrich cation concentrations in the adjacent solution, thus increasing the local supersaturation and promoting barite nucleation on organic films, even when the bulk solution was undersaturated. The Sr enrichment in barites formed on organic films was found to be controlled by solid-solution nucleation rates; instead, the Sr-poor barite formation in bulk solution was found to be controlled by solid-solution growth rates. This study provides a mechanistic explanation for Sr-rich marine barite formation and offers insights for understanding and controlling the compositions of solid solutions by separately tuning their nucleation and growth rates via the unique chemistry of solution-organic interfaces.
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15
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Zheng W, Demers JD, Lu X, Bergquist BA, Anbar AD, Blum JD, Gu B. Mercury Stable Isotope Fractionation during Abiotic Dark Oxidation in the Presence of Thiols and Natural Organic Matter. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:1853-1862. [PMID: 30371069 DOI: 10.1021/acs.est.8b05047] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Mercury (Hg) stable isotope fractionation has been widely used to trace Hg sources and transformations in the environment, although many important fractionation processes remain unknown. Here, we describe Hg isotope fractionation during the abiotic dark oxidation of dissolved elemental Hg(0) in the presence of thiol compounds and natural humic acid. We observe equilibrium mass-dependent fractionation (MDF) with enrichment of heavier isotopes in the oxidized Hg(II) and a small negative mass-independent fractionation (MIF) owing to nuclear volume effects. The measured enrichment factors for MDF and MIF (ε202Hg and E199Hg) ranged from 1.10‰ to 1.56‰ and from -0.16‰ to -0.18‰, respectively, and agreed well with theoretically predicted values for equilibrium fractionation between Hg(0) and thiol-bound Hg(II). We suggest that the observed equilibrium fractionation was likely controlled by isotope exchange between Hg(0) and Hg(II) following the production of the Hg(II)-thiol complex. However, significantly attenuated isotope fractionation was observed during the initial stage of Hg(0) oxidation by humic acid and attributed to the kinetic isotope effect (KIE). This research provides additional experimental constraints on interpreting Hg isotope signatures with important implications for the use of Hg isotope fractionation as a tracer of the Hg biogeochemical cycle.
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Affiliation(s)
- Wang Zheng
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37830 , United States
| | - Jason D Demers
- Department of Earth and Environmental Sciences , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Xia Lu
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37830 , United States
| | - Bridget A Bergquist
- Department of Earth Sciences , University of Toronto , 22 Russell Street , Toronto , Ontario M5S 3B1 , Canada
| | | | - Joel D Blum
- Department of Earth and Environmental Sciences , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Baohua Gu
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37830 , United States
- Department of Biosystems Engineering and Soil Science , University of Tennessee , Knoxville , Tennessee 37996 , United States
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16
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Correlation between molecular acidity (pKa) and vibrational spectroscopy. J Mol Model 2019; 25:48. [DOI: 10.1007/s00894-019-3928-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Accepted: 01/03/2019] [Indexed: 12/17/2022]
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17
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Chen S, Hou P, Wang J, Fu S, Liu L. A highly sensitive fluorescent probe based on the Michael addition mechanism with a large Stokes shift for cellular thiols imaging. Anal Bioanal Chem 2018; 410:4323-4330. [PMID: 29687249 DOI: 10.1007/s00216-018-1082-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Revised: 03/13/2018] [Accepted: 04/12/2018] [Indexed: 12/22/2022]
Abstract
A novel fluorescent probe IPY-MAL for thiols was developed based on imidazo[1,5-α]pyridine derivative, which was decorated with a maleimide group. The probe IPY-MAL showed a rapid response (30 s), high sensitivity and selectivity for thiols with a large Stokes shift (140 nm), which was triggered by the Michael addition reaction of thiols toward the C=C double bond of the maleimide group. Moreover, this probe IPY-MAL could quantitatively detect the concentrations of thiols ranging from 0 to 50 μM, and the detection limit was found to be as low as 28 nM. Cell imaging results indicated that the probe IPY-MAL could detect and visualize thiols in the living cells. Graphical abstract A novel imidazo[1,5-α]pyridine-based fluorescent probe was developed for sensitively monitoring and imaging thiols in living A549 cells with a large Stokes shift.
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Affiliation(s)
- Song Chen
- College of Pharmacy, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China.
| | - Peng Hou
- College of Pharmacy, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China
| | - Jing Wang
- College of Pharmacy, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China
| | - Shuang Fu
- College of Pharmacy, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China
| | - Lei Liu
- College of Pharmacy, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China
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18
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Lian P, Johnston RC, Parks JM, Smith JC. Quantum Chemical Calculation of pKas of Environmentally Relevant Functional Groups: Carboxylic Acids, Amines, and Thiols in Aqueous Solution. J Phys Chem A 2018; 122:4366-4374. [DOI: 10.1021/acs.jpca.8b01751] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Peng Lian
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
| | - Ryne C. Johnston
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
| | - Jerry M. Parks
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
| | - Jeremy C. Smith
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
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19
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Lee S, Kim DH, Kim KW. The enhancement and inhibition of mercury reduction by natural organic matter in the presence of Shewanella oneidensis MR-1. CHEMOSPHERE 2018; 194:515-522. [PMID: 29241125 DOI: 10.1016/j.chemosphere.2017.12.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 11/29/2017] [Accepted: 12/02/2017] [Indexed: 06/07/2023]
Abstract
Reduction-oxidation (Redox) processes of mercury (Hg) are of significant importance in influencing Hg speciation, bioavailability, and fate in anoxic environments where natural organic matter (NOM) and dissimilatory metal reducing bacteria (DMRB) are widely observed. However, the redox reaction between Hg and NOM, has not yet been studied in the presence of S. oneidensis MR-1 in anoxic environments. We have found that the reduction rate of mercuric mercury [Hg(II)] in the presence of Elliott soil humic acid (ESHA) was 0.02 h-1. It was faster than the rate (0.01 h-1) in the direct microbial Hg(II) reduction, suggesting that ESHA acts as an electron transfer mediator between cells and Hg, which enhances Hg(II) reduction under anoxic conditions. The overall rate of Hg(II) reduction in the presence of ESHA is determined by the rate of electron transfer from S. oneidensis MR-1 to ESHA (rate-limiting step) since the rate of electron transfer from reduced ESHA to Hg(II) was so rapid. In the reaction between S. oneidensis MR-1 and a variety of NOM analogs, the production rate of elemental mercury [Hg (0)] was linearly correlated with the free radical concentrations and aromaticities in reduced NOM analogs. However, at the high ESHA concentrations or cell contents, Hg(II) reduction might be inhibited by thiol functional groups in reduced ESHA and on cells. We suggest that the presence of NOM, cell concentration and NOM source can significantly affect the redox processes of Hg and therefore, have important implications for elucidating Hg redox processes under environmentally relevant complex conditions.
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Affiliation(s)
- Seyong Lee
- Center for Environmental Assessment Monitoring, Korea Environment Institute (KEI), 370 Sicheong-daero, Sejong, 30147, Republic of Korea
| | - Dong-Hun Kim
- Groundwater and Ecohydrology Research Center, Korea Institute of Geoscience and Mineral Resources (KIGAM), Gwahak-ro, Yuseoung-gu, Daejeon, 34132, Republic of Korea
| | - Kyoung-Woong Kim
- School of Earth Sciences & Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Republic of Korea.
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20
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Low-Molecular-Weight Thiols and Thioredoxins Are Important Players in Hg(II) Resistance in Thermus thermophilus HB27. Appl Environ Microbiol 2018; 84:AEM.01931-17. [PMID: 29150497 DOI: 10.1128/aem.01931-17] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Accepted: 10/24/2017] [Indexed: 12/31/2022] Open
Abstract
Mercury (Hg), one of the most toxic and widely distributed heavy metals, has a high affinity for thiol groups. Thiol groups reduce and sequester Hg. Therefore, low-molecular-weight (LMW) and protein thiols may be important cell components used in Hg resistance. To date, the role of low-molecular-weight thiols in Hg detoxification remains understudied. The mercury resistance (mer) operon of Thermus thermophilus suggests an evolutionary link between Hg(II) resistance and low-molecular-weight thiol metabolism. The mer operon encodes an enzyme involved in methionine biosynthesis, Oah. Challenge with Hg(II) resulted in increased expression of genes involved in the biosynthesis of multiple low-molecular-weight thiols (cysteine, homocysteine, and bacillithiol), as well as the thioredoxin system. Phenotypic analysis of gene replacement mutants indicated that Oah contributes to Hg resistance under sulfur-limiting conditions, and strains lacking bacillithiol and/or thioredoxins are more sensitive to Hg(II) than the wild type. Growth in the presence of either a thiol-oxidizing agent or a thiol-alkylating agent increased sensitivity to Hg(II). Furthermore, exposure to 3 μM Hg(II) consumed all intracellular reduced bacillithiol and cysteine. Database searches indicate that oah2 is present in all Thermus sp. mer operons. The presence of a thiol-related gene was also detected in some alphaproteobacterial mer operons, in which a glutathione reductase gene was present, supporting the role of thiols in Hg(II) detoxification. These results have led to a working model in which LMW thiols act as Hg(II)-buffering agents while Hg is reduced by MerA.IMPORTANCE The survival of microorganisms in the presence of toxic metals is central to life's sustainability. The affinity of thiol groups for toxic heavy metals drives microbe-metal interactions and modulates metal toxicity. Mercury detoxification (mer) genes likely originated early in microbial evolution in geothermal environments. Little is known about how mer systems interact with cellular thiol systems. Thermus spp. possess a simple mer operon in which a low-molecular-weight thiol biosynthesis gene is present, along with merR and merA In this study, we present experimental evidence for the role of thiol systems in mercury resistance. Our data suggest that, in T. thermophilus, thiolated compounds may function side by side with mer genes to detoxify mercury. Thus, thiol systems function in consort with mer-mediated resistance to mercury, suggesting exciting new questions for future research.
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21
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Yin Y, Xu W, Tan Z, Li Y, Wang W, Guo X, Yu S, Liu J, Jiang G. Photo- and thermo-chemical transformation of AgCl and Ag 2S in environmental matrices and its implication. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2017; 220:955-962. [PMID: 27836474 DOI: 10.1016/j.envpol.2016.10.081] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 10/19/2016] [Accepted: 10/27/2016] [Indexed: 06/06/2023]
Abstract
AgCl and Ag2S prevalently exist in the environment as minerals and/or the chlorination and sulfidation products of ionic silver and elemental silver nanoparticles (AgNPs). In this work, we investigated the chemical transformation of AgCl and Ag2S under simulated sunlight (in water) and incineration (in sludge and simulated municipal solid waste, SMSW). In the presence of natural organic matter, AgCl in river water was observed to be transformed into AgNPs under simulated sunlight, while photo-reduction of Ag2S could not take place under the same experimental conditions. During the course of incineration, pure Ag2S was transformed into elemental silver while AgCl remained stable; however, both Ag2S in sludge and AgCl in SMSW can be transformed to elemental silver under incineration, evident by the results of X-ray absorption spectroscopy and scanning electron microscopy measurements. Incineration temperature played an important role in the transformation of Ag2S and AgCl into elemental silver. These results suggest that chemical transformations of Ag2S and AgCl into elemental silver could be a possible source of naturally occurring or unintentionally produced AgNPs, affecting the fate, transport, bioavailability and toxicity of silver. Therefore, it is necessary to include the contributions of this transformation process when assessing the risk of ionic silver/AgNPs and the utilization and management of incineration residues.
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Affiliation(s)
- Yongguang Yin
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; Institute of Environment and Health, Jianghan University, Wuhan 430056, China
| | - Wei Xu
- Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - Zhiqiang Tan
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Yanbin Li
- Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
| | - Weidong Wang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Xiaoru Guo
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Sujuan Yu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Jingfu Liu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
| | - Guibin Jiang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
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22
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Wang Y, Schaefer JK, Mishra B, Yee N. Intracellular Hg(0) Oxidation in Desulfovibrio desulfuricans ND132. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:11049-11056. [PMID: 27654630 DOI: 10.1021/acs.est.6b03299] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The disposal of elemental mercury (Hg(0)) wastes in mining and manufacturing areas has caused serious soil and groundwater contamination issues. Under anoxic conditions, certain anaerobic bacteria can oxidize dissolved elemental mercury and convert the oxidized Hg to neurotoxic methylmercury. In this study, we conducted experiments with the Hg-methylating bacterium Desulfovibrio desulfuricans ND132 to elucidate the role of cellular thiols in anaerobic Hg(0) oxidation. The concentrations of cell-surface and intracellular thiols were measured, and specific fractions of D. desulfuricans ND132 were examined for Hg(0) oxidation activity and analyzed with extended X-ray absorption fine structure (EXAFS) spectroscopy. The experimental data indicate that intracellular thiol concentrations are approximately six times higher than those of the cell wall. Cells reacted with a thiol-blocking reagent were severely impaired in Hg(0) oxidation activity. Spheroplasts lacking cell walls rapidly oxidized Hg(0) to Hg(II), while cell wall fragments exhibited low reactivity toward Hg(0). EXAFS analysis of spheroplast samples revealed that multiple different forms of Hg-thiols are produced by the Hg(0) oxidation reaction and that the local coordination environment of the oxidized Hg changes with reaction time. The results of this study indicate that Hg(0) oxidation in D. desulfuricans ND132 is an intracellular process that occurs by reaction with thiol-containing molecules.
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Affiliation(s)
- Yuwei Wang
- Department of Environmental Sciences, Rutgers University , New Brunswick, New Jersey 08901, United States
| | - Jeffra K Schaefer
- Department of Environmental Sciences, Rutgers University , New Brunswick, New Jersey 08901, United States
| | - Bhoopesh Mishra
- Department of Physics, Illinois Institute of Technology , Chicago, Illinois 60616, United States
| | - Nathan Yee
- Department of Environmental Sciences, Rutgers University , New Brunswick, New Jersey 08901, United States
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23
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Luo HW. Effect of thiols enrichment on Cr(VI) photo-reduction by natural organic matter (NOM). CHEMOSPHERE 2016; 151:234-240. [PMID: 26946114 DOI: 10.1016/j.chemosphere.2016.02.103] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Revised: 01/30/2016] [Accepted: 02/23/2016] [Indexed: 06/05/2023]
Abstract
Photochemical redox transformation of Cr(VI)-NOM complexes substantially affects transport and speciation of less toxic Cr(III) in natural waters. However, the underlying mechanisms remain unclear. This study reported photochemical reactions of Cr(VI) with thiol-enriched NOM under acidic condition. More effective thiols enrichment in humic acid (HA) was observed than that in fulvic acid (FA), thereby resulting in a higher reduction capacity and faster rate of Cr(VI) photo-reduction. Chemical addition of sulfide to HA formed a large number of S-containing molecular formulae, which subsequently disappeared following reactions with Cr(VI) under solar irradiation. Cr(VI) photo-reduction in thiol-enriched HA consumed more S-containing formulae. Solar irradiation caused a rapid loss of the reduction capacities and thiol contents in HA and FA. All these findings can provide useful information for understanding the biogeochemical cycles of chromium and sulfur, and are also of environmental significance because they may partially account for photo-transformation of Cr(VI) when chromium enters into the aquatic environment as acidic industrial effluents.
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Affiliation(s)
- Hong-Wei Luo
- Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China; Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA; School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore.
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24
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Luo HW, Xu F. Bioreduction and reoxidation of uranium enhanced by thiol functional groups in natural organic matter. CHEMOSPHERE 2016; 147:20-24. [PMID: 26751128 DOI: 10.1016/j.chemosphere.2015.12.092] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 11/13/2015] [Accepted: 12/23/2015] [Indexed: 06/05/2023]
Abstract
Although natural organic matter (NOM) is known to affect biological reduction of U(VI) and subsequent reoxidation of U(IV), the underlying mechanisms remain unclear. This study investigated the redox reactions of sulfide with NOM to form thiol functional groups, which can greatly enhance U(VI) bioreduction and U(IV) reoxidation. Results showed that humic acid (HA) was found to be more effective than fulvic acid (FA) in producing thiol groups, both U(VI) bioreduction and U(IV) reoxidation rates increased with the increase of thiols content in HA and FA. These findings suggested that among other redox sites, thiol groups in NOM may play an important role in the electron transport between uranium and microbial cells, and are of great environmental implications because they provided direct proof that thiol groups are responsible for bioremediation and immobilization of uranium when it enters into the natural environments such as soil and groundwater.
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Affiliation(s)
- Hong-Wei Luo
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China; Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge 37830, TN, USA; School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore.
| | - Fang Xu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China
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Luo HW, Lin ZQ, Sheng GP. Spectroscopic characterization of the complexes between Fe/Mn and natural organic matters by electron paramagnetic resonance and synchrotron-based techniques. ECOTOXICOLOGY (LONDON, ENGLAND) 2015; 24:2207-2212. [PMID: 26403610 DOI: 10.1007/s10646-015-1551-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 09/16/2015] [Indexed: 06/05/2023]
Abstract
The surface interaction between heavy metals and natural organic matters (NOM) substantially affects their migration and conversion in natural environments. In this study, the chemical speciation and element mapping of Fe and Mn in reduced NOM were investigated. The results show that quinone and semiquinone moieties dominated the redox properties in NOM, and the EPR signal intensity exhibited pH dependence with an increase of EPR signal intensity at a higher pH value. The EPR results indicate that the complexes displayed the characteristics of superparamagnetic oxides/oxyhydroxides after Fe/Mn complexed with NOM. μ-XRF results suggest that the scatterplots of Fe and Mn distributions at pH 11 had the most positive linearly-related plot points, indicating strong correlations for Mn-Fe binary metallic ions. μ-XANES results further interpret the presence of higher Mn oxidation state at pH 11, while Fe kept trivalent in all samples. These results reveal that the surface interactions are closely related to the redox state of NOM and are beneficial for better understanding the speciation, immobilization, transport, and toxicity of metal ions in natural waters.
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Affiliation(s)
- Hong-Wei Luo
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China
| | - Zhi-Qi Lin
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China
| | - Guo-Ping Sheng
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
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Catrouillet C, Davranche M, Dia A, Bouhnik-Le Coz M, Pédrot M, Marsac R, Gruau G. Thiol groups controls on arsenite binding by organic matter: new experimental and modeling evidence. J Colloid Interface Sci 2015; 460:310-20. [PMID: 26348657 DOI: 10.1016/j.jcis.2015.08.045] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 08/22/2015] [Indexed: 11/28/2022]
Abstract
Although it has been suggested that several mechanisms can describe the direct binding of As(III) to organic matter (OM), more recently, the thiol functional group of humic acid (HA) was shown to be an important potential binding site for As(III). Isotherm experiments on As(III) sorption to HAs, that have either been grafted with thiol or not, were thus conducted to investigate the preferential As(III) binding sites. There was a low level of binding of As(III) to HA, which was strongly dependent on the abundance of the thiols. Experimental datasets were used to develop a new model (the modified PHREEQC-Model VI), which defines HA as a group of discrete carboxylic, phenolic and thiol sites. Protonation/deprotonation constants were determined for each group of sites (pKA=4.28±0.03; ΔpKA=2.13±0.10; pKB=7.11±0.26; ΔpKB=3.52±0.49; pKS=5.82±0.052; ΔpKS=6.12±0.12 for the carboxylic, phenolic and thiols sites, respectively) from HAs that were either grafted with thiol or not. The pKS value corresponds to that of single thiol-containing organic ligands. Two binding models were tested: the Mono model, which considered that As(III) is bound to the HA thiol site as monodentate complexes, and the Tri model, which considered that As(III) is bound as tridentate complexes. A simulation of the available literature datasets was used to validate the Mono model, with logKMS=2.91±0.04, i.e. the monodentate hypothesis. This study highlighted the importance of thiol groups in OM reactivity and, notably, determined the As(III) concentration bound to OM (considering that Fe is lacking or at least negligible) and was used to develop a model that is able to determine the As(III) concentrations bound to OM.
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Affiliation(s)
| | - Mélanie Davranche
- Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France
| | - Aline Dia
- Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France
| | | | - Mathieu Pédrot
- Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France
| | - Rémi Marsac
- Ecole Nationale Supérieure de Chimie de Rennes, UMR CNRS 6226 F-35708 Rennes cedex 7, France
| | - Gérard Gruau
- Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France
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Examining concentrations and molecular weights of thiols in microorganism cultures and in Churchill River (Manitoba) using a fluorescent-labeling method coupled to asymmetrical flow field-flow fractionation. Anal Bioanal Chem 2015; 407:4305-13. [DOI: 10.1007/s00216-015-8599-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2014] [Revised: 02/04/2015] [Accepted: 02/25/2015] [Indexed: 11/25/2022]
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28
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Chandan P, Ghosh S, Bergquist BA. Mercury isotope fractionation during aqueous photoreduction of monomethylmercury in the presence of dissolved organic matter. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:259-67. [PMID: 25399734 DOI: 10.1021/es5034553] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Monomethylmercury (MMHg) is a toxic pollutant that bioaccumulates in aquatic food webs. A major mechanism that limits MMHg uptake by biota is photodemethylation in surface waters. Recently, the extent of mass-independent fractionation (MIF) of Hg isotopes preserved in fish is being used to quantify this MMHg sink. Here, the effects of different types and amounts of DOM on Hg MIF during MMHg photodemethylation were investigated to assess how variable MIF enrichment factors may be with respect to changing DOM binding sites. From experiments conducted with varying amounts of reduced organic sulfur (S(red)-DOM), the extent and signature of MIF is likely dependent on whether MMHg is dominantly bound to S(red)-DOM. Similar enrichment factors were observed for low MMHg:S(red)-DOM experiments, where S(red)-DOM was in far excess of MMHg. In contrast, significantly lower and variable enrichment factors were observed for experiments with higher MMHg:S(red)-DOM ratios. Additionally the relationship between the two odd Hg isotopes that display MIF (Δ(199)Hg/Δ(201)Hg) was consistent for the low MMHg:S(red)-DOM experiments, while lower Δ(199)Hg/Δ(201)Hg relationships were observed for the higher MMHg:S(red)-DOM experiments. These results suggest that both the extent and signature of MMHg MIF are sensitive to different ligands that bind MMHg in nature.
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Affiliation(s)
- Priyanka Chandan
- University of Toronto , Department of Earth Sciences, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada
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Jiskra M, Saile D, Wiederhold JG, Bourdon B, Björn E, Kretzschmar R. Kinetics of Hg(II) exchange between organic ligands, goethite, and natural organic matter studied with an enriched stable isotope approach. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:13207-13217. [PMID: 25280234 DOI: 10.1021/es503483m] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The mobility and bioavailability of toxic Hg(II) in the environment strongly depends on its interactions with natural organic matter (NOM) and mineral surfaces. Using an enriched stable isotope approach, we investigated the exchange of Hg(II) between dissolved species (inorganically complexed or cysteine-, EDTA-, or NOM-bound) and solid-bound Hg(II) (carboxyl-/thiol-resin or goethite) over 30 days under constant conditions (pH, Hg and ligand concentrations). The Hg(II)-exchange was initially fast, followed by a slower phase, and depended on the properties of the dissolved ligands and sorbents. The results were described by a kinetic model allowing the simultaneous determination of adsorption and desorption rate coefficients. The time scales required to reach equilibrium with the carboxyl-resin varied greatly from 1.2 days for Hg(OH)2 to 16 days for Hg(II)-cysteine complexes and approximately 250 days for EDTA-bound Hg(II). Other experiments could not be described by an equilibrium model, suggesting that a significant fraction of total-bound Hg was present in a non-exchangeable form (thiol-resin and NOM: 53-58%; goethite: 22-29%). Based on the slow and incomplete exchange of Hg(II) described in this study, we suggest that kinetic effects must be considered to a greater extent in the assessment of the fate of Hg in the environment and the design of experimental studies, for example, for stability constant determination or metal isotope fractionation during sorption.
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Affiliation(s)
- Martin Jiskra
- Soil Chemistry, Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich , CH-8092 Zurich, Switzerland
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Lin H, Morrell-Falvey JL, Rao B, Liang L, Gu B. Coupled mercury-cell sorption, reduction, and oxidation on methylmercury production by Geobacter sulfurreducens PCA. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:11969-76. [PMID: 25268220 DOI: 10.1021/es502537a] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
G. sulfurreducens PCA cells have been shown to reduce, sorb, and methylate Hg(II) species, but it is unclear whether this organism can oxidize and methylate dissolved elemental Hg(0) as shown for Desulfovibrio desulfuricans ND132. Using Hg(II) and Hg(0) separately as Hg sources in washed cell assays in phosphate buffered saline (pH 7.4), we report how cell-mediated Hg reduction and oxidation compete or synergize with sorption, thus affecting the production of toxic methylmercury by PCA cells. Methylation is found to be positively correlated to Hg sorption (r = 0.73) but negatively correlated to Hg reduction (r = -0.62). These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (-SH). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell-SH molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 × 10(-19) to 25 × 10(-19) moles-Hg/cell (equivalent to Hg/cell-SH of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant ΔomcBESTZ also shows decreases in Hg reduction and increases in methylation. However, the presence of competing thiol-binding ions such as Zn(2+) leads to increased Hg reduction and decreased methylation. These results suggest that the coupled cell-Hg sorption and redox transformations are important in controlling the rates of Hg uptake and methylation by G. sulfurreducens PCA in anoxic environments.
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Affiliation(s)
- Hui Lin
- Environmental Sciences Division and ‡Biosciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
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