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Joshi S, Gangola S, Bhandari G, Bhandari NS, Nainwal D, Rani A, Malik S, Slama P. Rhizospheric bacteria: the key to sustainable heavy metal detoxification strategies. Front Microbiol 2023; 14:1229828. [PMID: 37555069 PMCID: PMC10405491 DOI: 10.3389/fmicb.2023.1229828] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2023] [Accepted: 07/10/2023] [Indexed: 08/10/2023] Open
Abstract
The increasing rate of industrialization, anthropogenic, and geological activities have expedited the release of heavy metals (HMs) at higher concentration in environment. HM contamination resulting due to its persistent nature, injudicious use poses a potential threat by causing metal toxicities in humans and animals as well as severe damage to aquatic organisms. Bioremediation is an emerging and reliable solution for mitigation of these contaminants using rhizospheric microorganisms in an environmentally safe manner. The strategies are based on exploiting microbial metabolism and various approaches developed by plant growth promoting bacteria (PGPB) to minimize the toxicity concentration of HM at optimum levels for the environmental clean-up. Rhizospheric bacteria are employed for significant growth of plants in soil contaminated with HM. Exploitation of bacteria possessing plant-beneficial traits as well as metal detoxifying property is an economical and promising approach for bioremediation of HM. Microbial cells exhibit different mechanisms of HM resistance such as active transport, extra cellular barrier, extracellular and intracellular sequestration, and reduction of HM. Tolerance of HM in microorganisms may be chromosomal or plasmid originated. Proteins such as MerT and MerA of mer operon and czcCBA, ArsR, ArsA, ArsD, ArsB, and ArsC genes are responsible for metal detoxification in bacterial cell. This review gives insights about the potential of rhizospheric bacteria in HM removal from various polluted areas. In addition, it also gives deep insights about different mechanism of action expressed by microorganisms for HM detoxification. The dual-purpose use of biological agent as plant growth enhancement and remediation of HM contaminated site is the most significant future prospect of this article.
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Affiliation(s)
- Samiksha Joshi
- School of Agriculture, Graphic Era Hill University, Bhimtal, India
| | - Saurabh Gangola
- School of Agriculture, Graphic Era Hill University, Bhimtal, India
| | - Geeta Bhandari
- Department of Biosciences, Himalayan School of Bio Sciences, Swami Rama Himalayan University, Dehradun, India
| | | | - Deepa Nainwal
- School of Agriculture, Graphic Era Hill University, Bhimtal, India
| | - Anju Rani
- Department of Life Sciences, Graphic Era (Deemed to be) University, Dehradun, Uttarakhand, India
| | - Sumira Malik
- Amity Institute of Biotechnology, Amity University Jharkhand, Ranchi, India
- Guru Nanak College of Pharmaceutical Sciences, Dehradun, Uttarakhand, India
- Department of Applied Sciences, Uttaranchal University, Dehradun, Uttarakhand, India
| | - Petr Slama
- Laboratory of Animal Immunology and Biotechnology, Department of Animal Morphology, Physiology and Genetics, Faculty of AgriSciences, Mendel University in Brno, Brno, Czechia
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Ferreira G, Santander A, Chavarría L, Cardozo R, Savio F, Sobrevia L, Nicolson GL. Functional consequences of lead and mercury exposomes in the heart. Mol Aspects Med 2021; 87:101048. [PMID: 34785060 DOI: 10.1016/j.mam.2021.101048] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 11/02/2021] [Accepted: 11/03/2021] [Indexed: 12/20/2022]
Abstract
Lead and mercury are heavy metals that are highly toxic to life forms. There are no known physiological processes that require them, and they do not have a particular threshold concentration to produce biologic damage. They are non-biodegradable, and they slowly accumulate in the environment in a dynamic equilibrium between air, water, soil, food, and living organisms. Their accumulation in the environment has been increasing over time, because they were not banned from use in anthropogenic industrial production. In their +2 cationic state they are powerful oxidizing agents with the ability to interfere significantly with processes that require specific divalent cations. Acute or chronic exposure to lead and mercury can produce multisystemic damage, especially in the developing nervous systems of children and fetuses, resulting in variety of neurological consequences. They can also affect the cardiovascular system and especially the heart, either directly through their action on cardiomyocytes or indirectly through their effects on innervation, humoral responses or blood vessel alterations. For example, heart function modified by these heavy metals are heart rate, contraction, excitability, and rhythm. Some cardiac molecular targets have been identified and characterized. The direct mechanisms of damage of these heavy metals on heart function are discussed. We conclude that exposome to these heavy metals, should be considered as a major relevant risk factor for cardiac diseases.
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Affiliation(s)
- Gonzalo Ferreira
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling. Department of Biophysics, Faculty of Medicine, Universidad de la República, Gral. Flores, 2125, CP 11800, Montevideo, Uruguay.
| | - Axel Santander
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling. Department of Biophysics, Faculty of Medicine, Universidad de la República, Gral. Flores, 2125, CP 11800, Montevideo, Uruguay
| | - Luisina Chavarría
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling. Department of Biophysics, Faculty of Medicine, Universidad de la República, Gral. Flores, 2125, CP 11800, Montevideo, Uruguay
| | - Romina Cardozo
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling. Department of Biophysics, Faculty of Medicine, Universidad de la República, Gral. Flores, 2125, CP 11800, Montevideo, Uruguay
| | - Florencia Savio
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling. Department of Biophysics, Faculty of Medicine, Universidad de la República, Gral. Flores, 2125, CP 11800, Montevideo, Uruguay
| | - Luis Sobrevia
- Cellular and Molecular Physiology Laboratory (CMPL), Department of Obstetrics, Division of Obstetrics and Gynaecology, Universidad Católica de Chile, Santiago, 8330024, Chile; Department of Physiology, Faculty of Pharmacy, Universidad de Sevilla, Seville, E-41012, Spain; Medical School (Faculty of Medicine), São Paulo State University (UNESP), Brazil; University of Queensland Centre for Clinical Research (UQCCR), Faculty of Medicine and Biomedical Sciences, University of Queensland, Herston, QLD 4029, Queensland, Australia; Department of Pathology and Medical Biology, University of Groningen, University Medical Center Groningen, 9713GZ, Groningen, the Netherlands
| | - Garth L Nicolson
- Department of Molecular Pathology, The Institute for Molecular Medicine, 16731 Gothard St. Huntington Beach, California, 92647, USA
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Pal A, Bhattacharjee S, Saha J, Sarkar M, Mandal P. Bacterial survival strategies and responses under heavy metal stress: a comprehensive overview. Crit Rev Microbiol 2021; 48:327-355. [PMID: 34473592 DOI: 10.1080/1040841x.2021.1970512] [Citation(s) in RCA: 49] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Heavy metals bring long-term hazardous consequences and pose a serious threat to all life forms. Being non-biodegradable, they can remain in the food webs for a long period of time. Metal ions are essential for life and indispensable for almost all aspects of metabolism but can be toxic beyond threshold level to all living beings including microbes. Heavy metals are generally present in the environment, but many geogenic and anthropogenic activities has led to excess metal ion accumulation in the environment. To survive in harsh metal contaminated environments, bacteria have certain resistance mechanisms to metabolize and transform heavy metals into less hazardous forms. This also gives rise to different species of heavy metal resistant bacteria. Herein, we have tried to incorporate the different aspects of heavy metal toxicity in bacteria and provide an up-to-date and across-the-board review. The various aspects of heavy metal biology of bacteria encompassed in this review includes the biological notion of heavy metals, toxic effect of heavy metals on bacteria, the factors regulating bacterial heavy metal resistance, the diverse mechanisms governing bacterial heavy metal resistance, bacterial responses to heavy metal stress, and a brief overview of gene regulation under heavy metal stress.
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Affiliation(s)
- Ayon Pal
- Microbiology and Computational Biology Laboratory, Department of Botany, Raiganj University, Raiganj, India
| | - Sukanya Bhattacharjee
- Microbiology and Computational Biology Laboratory, Department of Botany, Raiganj University, Raiganj, India
| | - Jayanti Saha
- Microbiology and Computational Biology Laboratory, Department of Botany, Raiganj University, Raiganj, India
| | - Monalisha Sarkar
- Mycology and Plant Pathology Laboratory, Department of Botany, Raiganj University, Raiganj, India
| | - Parimal Mandal
- Mycology and Plant Pathology Laboratory, Department of Botany, Raiganj University, Raiganj, India
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Ohshiro Y, Uraguchi S, Nakamura R, Takanezawa Y, Kiyono M. Cadmium transport activity of four mercury transporters (MerC, MerE, MerF and MerT) and effects of the periplasmic mercury-binding protein MerP on Mer-dependent cadmium uptake. FEMS Microbiol Lett 2020; 367:5942867. [PMID: 33119092 DOI: 10.1093/femsle/fnaa177] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Accepted: 10/27/2020] [Indexed: 11/13/2022] Open
Abstract
Mercury superfamily proteins, i.e. inner membrane-spanning proteins (MerC, MerE, MerF and MerT) and a periplasmic mercury-binding protein (MerP), transport mercury into the cytoplasm. A previous study demonstrated that a Mer transporter homolog exhibits cadmium transport activity; based on this, the present study aimed to evaluate the cadmium transport activity of MerC, MerE, MerF and MerT and the effects of MerP co-expression in Escherichia coli. Bacteria expressing MerC, MerE, MerF or MerT without MerP were more sensitive to cadmium and significantly absorbed more cadmium than did the control strain. Expression of MerP in combination with MerC, MerE, MerF or MerT increased the bacterial sensitivity to cadmium and cadmium accumulation compared to a single expression of MerC, MerE, MerF or MerT. Cadmium uptake mediated by MerC, MerE, MerF or MerT was inhibited under cold or acidic conditions. These findings suggest that MerC, MerE, MerF and MerT are broad-spectrum heavy metal transporters that mediate both mercury and cadmium transport into cells and that MerP accelerates the cadmium transport ability of MerC, MerE, MerF and MerT.
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Affiliation(s)
- Yuka Ohshiro
- Department of Public Health, School of Pharmacy, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Shimpei Uraguchi
- Department of Public Health, School of Pharmacy, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Ryosuke Nakamura
- Department of Public Health, School of Pharmacy, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Yasukazu Takanezawa
- Department of Public Health, School of Pharmacy, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
| | - Masako Kiyono
- Department of Public Health, School of Pharmacy, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
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Chen CT, Liao YY, Salunke SB, Lin YH, Kuo TS. Directed Self-Assembly of C 4-Symmetric, Oxidovanadate-Centered, Vanadyl(V) Quadruplexes for Ba 2+- and Hg 2+-Specific Recognition, Transport, and Recovery. Inorg Chem 2018; 57:11511-11523. [PMID: 30183263 DOI: 10.1021/acs.inorgchem.8b01454] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Directed assembly of loosely, Na+-bound, oxidovanadate-centered quartets of C4-symmetry from tailor-made chiral N-salicylidene-vanadyl(V) complexes, for the first time, allows for highly efficient Ba2+- or Hg2+-specific detection (by 51V NMR and VCD), transport (forming a unique helical capsule or a capped square planar complex, respectively), and green recovery from an aqueous phase containing 4 different alkaline earth ions or from at least 10 different metal ions of similar size and charge capacity into the CHCl3 layer without interference from oxa- or oxophilic ions like Mg2+, Ca2+, Cu2+, Cd2+, and Pb2+.
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Affiliation(s)
- Chien-Tien Chen
- Department of Chemistry , National Tsing Hua University , Hsinchu , Taiwan
| | - Yi-Ya Liao
- Department of Chemistry , National Tsing Hua University , Hsinchu , Taiwan
| | | | - Ya-Hui Lin
- National Taiwan Normal University , Taipei , Taiwan
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6
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Sone Y, Uraguchi S, Takanezawa Y, Nakamura R, Pan-Hou H, Kiyono M. Cysteine and histidine residues are involved in Escherichia coli Tn 21 MerE methylmercury transport. FEBS Open Bio 2017; 7:1994-1999. [PMID: 29226085 PMCID: PMC5715351 DOI: 10.1002/2211-5463.12341] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Revised: 10/05/2017] [Accepted: 10/24/2017] [Indexed: 11/29/2022] Open
Abstract
Bacterial resistance to mercury compounds (mercurials) is mediated by proteins encoded by mercury resistance (mer) operons. Six merE variants with site‐directed mutations were constructed to investigate the roles of the cysteine and histidine residues in MerE protein during mercurial transport. By comparison of mercurial uptake by the cell with intact and/or variant MerE, we showed that the cysteine pair in the first transmembrane domain was critical for the transport of both Hg(II) and CH3Hg(I). Also, the histidine residue located near to the cysteine pair was critical for Hg(II) transport, whereas the histidine residue located on the periplasmic side was critical for CH3Hg(I) transport. Thus, enhanced mercurial uptake mediated by MerE may be a promising strategy for the design of new biomass for use in the bioremediation of mercurials in the environment.
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Affiliation(s)
- Yuka Sone
- Department of Public Health School of Pharmacy Kitasato University Tokyo Japan
| | - Shimpei Uraguchi
- Department of Public Health School of Pharmacy Kitasato University Tokyo Japan
| | - Yasukazu Takanezawa
- Department of Public Health School of Pharmacy Kitasato University Tokyo Japan
| | - Ryosuke Nakamura
- Department of Public Health School of Pharmacy Kitasato University Tokyo Japan
| | | | - Masako Kiyono
- Department of Public Health School of Pharmacy Kitasato University Tokyo Japan
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7
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Wu W, Huang H, Ling Z, Yu Z, Jiang Y, Liu P, Li X. Genome sequencing reveals mechanisms for heavy metal resistance and polycyclic aromatic hydrocarbon degradation in Delftia lacustris strain LZ-C. ECOTOXICOLOGY (LONDON, ENGLAND) 2016; 25:234-247. [PMID: 26589947 DOI: 10.1007/s10646-015-1583-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 10/30/2015] [Indexed: 06/05/2023]
Abstract
Strain LZ-C, isolated from a petrochemical wastewater discharge site, was found to be resistant to heavy metals and to degrade various aromatic compounds, including naphenol, naphthalene, 2-methylnaphthalene and toluene. Data obtained from 16S rRNA gene sequencing showed that this strain was closely related to Delftia lacustris. The 5,889,360 bp genome of strain LZ-C was assembled into 239 contigs and 197 scaffolds containing 5855 predicted open reading frames (ORFs). Among these predicted ORFs, 464 were different from the type strain of Delftia. The minimal inhibitory concentrations were 4 mM, 30 µM, 2 mM and 1 mM for Cr(VI), Hg(II), Cd(II) and Pb(II), respectively. Both genome sequencing and quantitative real-time PCR data revealed that genes related to Chr, Czc and Mer family genes play important roles in heavy metal resistance in strain LZ-C. In addition, the Na(+)/H(+) antiporter NhaA is important for adaptation to high salinity resistance (2.5 M NaCl). The complete pathways of benzene and benzoate degradation were identified through KEGG analysis. Interestingly, strain LZ-C also degrades naphthalene but lacks the key naphthalene degradation gene NahA. Thus, we propose that strain LZ-C exhibits a novel protein with a function similar to NahA. This study is the first to reveal the mechanisms of heavy metal resistance and salinity tolerance in D. lacustris and to identify a potential 2-methylnaphthalene degradation protein in this strain. Through whole-genome sequencing analysis, strain LZ-C might be a good candidate for the bioremediation of heavy metals and polycyclic aromatic hydrocarbons.
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Affiliation(s)
- Wenyang Wu
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China
| | - Haiying Huang
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China
| | - Zhenmin Ling
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China
| | - Zhengsheng Yu
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China
| | - Yiming Jiang
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China
| | - Pu Liu
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China
| | - Xiangkai Li
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China.
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8
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Overexpression, purification and biophysical characterisation of E. coli MerT. Protein Expr Purif 2015; 108:85-89. [DOI: 10.1016/j.pep.2014.11.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Revised: 11/21/2014] [Accepted: 11/24/2014] [Indexed: 11/18/2022]
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9
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Lucchetti-Miganeh C, Redelberger D, Chambonnier G, Rechenmann F, Elsen S, Bordi C, Jeannot K, Attrée I, Plésiat P, de Bentzmann S. Pseudomonas aeruginosa Genome Evolution in Patients and under the Hospital Environment. Pathogens 2014; 3:309-40. [PMID: 25437802 PMCID: PMC4243448 DOI: 10.3390/pathogens3020309] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2013] [Revised: 03/26/2014] [Accepted: 03/28/2014] [Indexed: 11/21/2022] Open
Abstract
Pseudomonas aeruginosa is a Gram-negative environmental species and an opportunistic microorganism, establishing itself in vulnerable patients, such as those with cystic fibrosis (CF) or those hospitalized in intensive care units (ICU). It has become a major cause of nosocomial infections worldwide and a serious threat to Public Health because of overuse and misuse of antibiotics that have selected highly resistant strains against which very few therapeutic options exist. Herein is illustrated the intraclonal evolution of the genome of sequential isolates collected in a single CF patient from the early phase of pulmonary colonization to the fatal outcome. We also examined at the whole genome scale a pair of genotypically-related strains made of a drug susceptible, environmental isolate recovered from an ICU sink and of its multidrug resistant counterpart found to infect an ICU patient. Multiple genetic changes accumulated in the CF isolates over the disease time course including SNPs, deletion events and reduction of whole genome size. The strain isolated from the ICU patient displayed an increase in the genome size of 4.8% with major genetic rearrangements as compared to the initial environmental strain. The annotated genomes are given in free access in an interactive web application WallGene designed to facilitate large-scale comparative analysis and thus allowing investigators to explore homologies and syntenies between P. aeruginosa strains, here PAO1 and the five clinical strains described.
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Affiliation(s)
| | - David Redelberger
- UMR7255-Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS-Aix Marseille University, Marseille 13402, France.
| | - Gaël Chambonnier
- UMR7255-Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS-Aix Marseille University, Marseille 13402, France.
| | | | - Sylvie Elsen
- INSERM, UMR-S 1036, Biology of Cancer and Infection, Grenoble 38054, France.
| | - Christophe Bordi
- UMR7255-Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS-Aix Marseille University, Marseille 13402, France.
| | - Katy Jeannot
- Laboratoire de Bactériologie, Faculté de Médecine-Pharmacie, Université de Franche-Comté, Besançon 25030, France.
| | - Ina Attrée
- INSERM, UMR-S 1036, Biology of Cancer and Infection, Grenoble 38054, France.
| | - Patrick Plésiat
- Laboratoire de Bactériologie, Faculté de Médecine-Pharmacie, Université de Franche-Comté, Besançon 25030, France.
| | - Sophie de Bentzmann
- UMR7255-Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS-Aix Marseille University, Marseille 13402, France.
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Foucault Y, Durand MJ, Tack K, Schreck E, Geret F, Leveque T, Pradere P, Goix S, Dumat C. Use of ecotoxicity test and ecoscores to improve the management of polluted soils: case of a secondary lead smelter plant. JOURNAL OF HAZARDOUS MATERIALS 2013; 246-247:291-299. [PMID: 23328625 DOI: 10.1016/j.jhazmat.2012.12.042] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2012] [Revised: 11/27/2012] [Accepted: 12/26/2012] [Indexed: 06/01/2023]
Abstract
With the rise of sustainable development, rehabilitation of brownfield sites located in urban areas has become a major concern. Management of contaminated soils in relation with environmental and sanitary risk concerns is therefore a strong aim needing the development of both useful tools for risk assessment and sustainable remediation techniques. For soils polluted by metals and metalloids (MTE), the criteria for landfilling are currently not based on ecotoxicological tests but on total MTE concentrations and leaching tests. In this study, the ecotoxicity of leachates from MTE polluted soils sampled from an industrial site recycling lead-acid batteries were evaluated by using both modified Escherichia coli strains with luminescence modulated by metals and normalized Daphnia magna and Alivibrio fischeri bioassays. The results were clearly related to the type of microorganisms (crustacean, different strains of bacteria) whose sensitivity varied. Ecotoxicity was also different according to sample location on the site, total concentrations and physico-chemical properties of each soil. For comparison, standard leaching tests were also performed. Potentially phytoavailable fraction of MTE in soils and physico-chemical measures were finally performed in order to highlight the mechanisms. The results demonstrated that the use of a panel of microorganisms is suitable for hazard classification of polluted soils. In addition, calculated eco-scores permit to rank the polluted soils according to their potentially of dangerousness. Influence of soil and MTE characteristics on MTE mobility and ecotoxicity was also highlighted.
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Affiliation(s)
- Yann Foucault
- Université de Toulouse, INP-ENSAT, Avenue de l'Agrobiopôle, 31326 Castanet-Tolosan, France
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11
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Allen RC, Tu YK, Nevarez MJ, Bobbs AS, Friesen JW, Lorsch JR, McCauley JA, Voet JG, Hamlett NV. The mercury resistance (mer) operon in a marine gliding flavobacterium, Tenacibaculum discolor 9A5. FEMS Microbiol Ecol 2012; 83:135-48. [PMID: 22816663 DOI: 10.1111/j.1574-6941.2012.01460.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 07/17/2012] [Accepted: 07/18/2012] [Indexed: 01/18/2023] Open
Abstract
Genes conferring mercury resistance have been investigated in a variety of bacteria and archaea but not in bacteria of the phylum Bacteroidetes, despite their importance in many environments. We found, however, that a marine gliding Bacteroidetes species, Tenacibaculum discolor, was the predominant mercury-resistant bacterial taxon cultured from a salt marsh fertilized with mercury-contaminated sewage sludge. Here we report characterization of the mercuric reductase and the narrow-spectrum mercury resistance (mer) operon from one of these strains - T. discolor 9A5. This mer operon, which confers mercury resistance when cloned into Flavobacterium johnsoniae, encodes a novel mercury-responsive ArsR/SmtB family transcriptional regulator that appears to have evolved independently from other mercury-responsive regulators, a novel putative transport protein consisting of a fusion between the integral membrane Hg(II) transporter MerT and the periplasmic Hg(II)-binding protein MerP, an additional MerP protein, and a mercuric reductase that is phylogenetically distinct from other known mercuric reductases.
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Affiliation(s)
- Rachel C Allen
- Program in Molecular Biology, Pomona College, Claremont, CA, USA
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12
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Ghoshal S, Bhattacharya P, Chowdhury R. De-mercurization of wastewater by Bacillus cereus (JUBT1): growth kinetics, biofilm reactor study and field emission scanning electron microscopic analysis. JOURNAL OF HAZARDOUS MATERIALS 2011; 194:355-361. [PMID: 21872987 DOI: 10.1016/j.jhazmat.2011.07.109] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 07/13/2011] [Accepted: 07/29/2011] [Indexed: 05/31/2023]
Abstract
Removal of mercuric ions by a mercury resistant bacteria, called Bacillus cereus (JUBT1), isolated from the sludge of a local chlor-alkali industry, has been investigated. Growth kinetics of the bacteria have been determined. A multiplicative, non-competitive relationship between sucrose and mercury ions has been observed with respect to bacterial growth. A combination of biofilm reactor, using attached growth of Bacillus cereus (JUBT1) on rice husk packing, and an activated carbon filter has been able to ensure the removal of mercury up to near-zero level. Energy dispersive spectrometry analysis of biofilm and the activated carbon has proved the transformation of Hg(2+) to Hg(0) and its confinement in the system.
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Affiliation(s)
- Sanjukta Ghoshal
- Chemical Engineering Department, Jadavpur University Kolkata 700 032, West Bengal, India
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13
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Sone Y, Pan-Hou H, Nakamura R, Sakabe K, Kiyono M. Roles Played by MerE and MerT in the Transport of Inorganic and Organic Mercury Compounds in Gram-negative Bacteria. ACTA ACUST UNITED AC 2010. [DOI: 10.1248/jhs.56.123] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Yuka Sone
- Department of Public Health and Molecular Toxicology, School of Pharmacy, Kitasato University
| | | | - Ryosuke Nakamura
- Department of Public Health and Molecular Toxicology, School of Pharmacy, Kitasato University
| | - Kou Sakabe
- Department of Public Health and Molecular Toxicology, School of Pharmacy, Kitasato University
- Department of Human Structure and Function, Tokai University School of Medicine
| | - Masako Kiyono
- Department of Public Health and Molecular Toxicology, School of Pharmacy, Kitasato University
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14
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Kiyono M, Sone Y, Nakamura R, Pan-Hou H, Sakabe K. The MerE protein encoded by transposon Tn21 is a broad mercury transporter in Escherichia coli. FEBS Lett 2009; 583:1127-31. [PMID: 19265693 DOI: 10.1016/j.febslet.2009.02.039] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2009] [Revised: 02/24/2009] [Accepted: 02/25/2009] [Indexed: 10/21/2022]
Abstract
In order to clarify the physiological role of the merE gene of transposon Tn21, a pE4 plasmid that contained the merR gene of plasmid pMR26 from Pseudomonas strain K-62, and the merE gene of Tn21 from the Shigella flexneri plasmid NR1 (R100) was constructed. Bacteria with plasmid pE4 (merR-o/p-merE) were more hypersensitive to CH(3)Hg(I) and Hg(II), and took up significantly more CH(3)Hg(I) and Hg(II), than the isogenic strain. The MerE protein encoded by pE4 was localized in the membrane cell fraction, but not in the soluble fraction. Based on these experimental results, we suggest for the first time that the merE gene is a broad mercury transporter mediating the transport of both CH(3)Hg(I) and Hg(II) across the bacterial membrane.
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Affiliation(s)
- Masako Kiyono
- Department of Public Health and Molecular Toxicology, School of Pharmacy, Kitasato University, Tokyo, Japan.
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15
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Holmes DE, O'Neil RA, Chavan MA, N'Guessan LA, Vrionis HA, Perpetua LA, Larrahondo MJ, DiDonato R, Liu A, Lovley DR. Transcriptome of Geobacter uraniireducens growing in uranium-contaminated subsurface sediments. ISME JOURNAL 2008; 3:216-30. [PMID: 18843300 DOI: 10.1038/ismej.2008.89] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
To learn more about the physiological state of Geobacter species living in subsurface sediments, heat-sterilized sediments from a uranium-contaminated aquifer in Rifle, Colorado, were inoculated with Geobacter uraniireducens, a pure culture representative of the Geobacter species that predominates during in situ uranium bioremediation at this site. Whole-genome microarray analysis comparing sediment-grown G. uraniireducens with cells grown in defined culture medium indicated that there were 1084 genes that had higher transcript levels during growth in sediments. Thirty-four c-type cytochrome genes were upregulated in the sediment-grown cells, including several genes that are homologous to cytochromes that are required for optimal Fe(III) and U(VI) reduction by G. sulfurreducens. Sediment-grown cells also had higher levels of transcripts, indicative of such physiological states as nitrogen limitation, phosphate limitation and heavy metal stress. Quantitative reverse transcription PCR showed that many of the metabolic indicator genes that appeared to be upregulated in sediment-grown G. uraniireducens also showed an increase in expression in the natural community of Geobacter species present during an in situ uranium bioremediation field experiment at the Rifle site. These results demonstrate that it is feasible to monitor gene expression of a microorganism growing in sediments on a genome scale and that analysis of the physiological status of a pure culture growing in subsurface sediments can provide insights into the factors controlling the physiology of natural subsurface communities.
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Affiliation(s)
- Dawn E Holmes
- Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA.
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16
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Effect of pH on intracellular accumulation of trace concentrations of Hg(II) in Escherichia coli under anaerobic conditions, as measured using a mer-lux bioreporter. Appl Environ Microbiol 2007; 74:667-75. [PMID: 18083863 DOI: 10.1128/aem.00717-07] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The effects of pH on the uptake and accumulation of Hg(II) by Escherichia coli were determined at trace, environmentally relevant, concentrations of Hg and under anaerobic conditions. Hg(II) accumulation was measured using inducible light production from E. coli HMS174 harboring a mer-lux bioreporter plasmid (pRB28). The effect of pH on the toxicity of higher concentrations of Hg(II) was measured using a constitutive lux plasmid (pRB27) in the same bacterial host. In this study, intracellular accumulation and toxicity of Hg(II) under anaerobic conditions were both significantly enhanced with decreasing pH over the pH range of 8 to 5. The pH effect on Hg(II) accumulation was most pronounced at pHs of <6, which substantially enhanced the Hg(II)-dependent light response. This enhanced response did not appear to be due to pH stress, as similar results were obtained whether cells were grown at the same pH as the assay or at a different pH. The enhanced accumulation of Hg(II) was also not related to differences in the chemical speciation of Hg(II) in the external medium resulting from the changes in pH. Experiments with Cd(II), also detectable by the mer-lux bioreporter system, showed that Cd(II) accumulation responded differently to pH changes than the net accumulation of Hg(II). Potential implications of these findings for our understanding of bacterial accumulation of Hg(II) under anaerobic conditions and for bacteria-mediated cycling of Hg(II) in aquatic ecosystems are discussed. Arguments are provided suggesting that this differential accumulation is due to changes in uptake of mercury.
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17
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Haines AS, Jones K, Batt SM, Kosheleva IA, Thomas CM. Sequence of plasmid pBS228 and reconstruction of the IncP-1α phylogeny. Plasmid 2007; 58:76-83. [PMID: 17320955 DOI: 10.1016/j.plasmid.2007.01.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2006] [Revised: 12/21/2006] [Accepted: 01/02/2007] [Indexed: 11/29/2022]
Abstract
The antibiotic resistance plasmid pBS228 has been completely sequenced, and revealed to be descended from a plasmid virtually identical to the Birmingham IncP-1alpha plasmid RK2/RP4/RP1. However, it has three additional transposon insertions, one of which is responsible for the extra antibiotic resistances conferred. Loss of kanamycin resistance, which is characteristic of most IncP-1alpha plasmids, is the result of this insertion. A second transposon causes inactivation of the mating pair formation apparatus, rendering the plasmid non-self-transmissible. Comparison with the published data for other IncP-1alpha plasmids gives insight into the recent evolutionary history of this group as well as the acquisition and transmission of one of the first ampicillin resistance transposons discovered.
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Affiliation(s)
- Anthony S Haines
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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18
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Belzile N, Wu GJ, Chen YW, Appanna VD. Detoxification of selenite and mercury by reduction and mutual protection in the assimilation of both elements by Pseudomonas fluorescens. THE SCIENCE OF THE TOTAL ENVIRONMENT 2006; 367:704-14. [PMID: 16626785 DOI: 10.1016/j.scitotenv.2006.03.008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2006] [Revised: 03/02/2006] [Accepted: 03/06/2006] [Indexed: 05/08/2023]
Abstract
A study on the assimilation and detoxification of selenium and mercury and on the interaction between these two elements was conducted on Pseudomonas fluorescens. P. fluorescens was able to convert separately both elements to their elemental forms, which are less toxic and biologically less available. To study the converting mechanism of selenite to elemental Se, cells were grown in the presence of various selenite concentrations and several parameters such as extracellular protein concentrations, pH, carbohydrate concentrations, isocitrate dehydrogenase (ICDH) and malic enzyme were monitored. Transmission electron microscopy (TEM) and various analytical methods were applied to confirm the interaction between selenium and cell. The former appeared as a red precipitate localized predominantly in the consumed culture medium. P. fluorescens also resisted to the toxic effect of mercury by converting Hg2+ to the volatile and less toxic form Hg0. Mercury reductase was likely responsible for the conversion of Hg2+ to Hg0. More importantly, the interaction between mercury and selenium was also studied. The presence of selenite significantly reduced the accumulation of mercury in P. fluorescens. It was also interesting to note that mercury appeared to behave as a protecting agent against selenium intoxication as the bioaccumulation of Se was also inhibited by this metal. The formation of Se-Hg complexes could explain this mutual protective effect. No precipitate of elemental Se could be detected when Hg was present in the cultures.
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Affiliation(s)
- Nelson Belzile
- Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario, Canada, P3E 2C6.
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19
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Kinscherf TG, Willis DK. The biosynthetic gene cluster for the beta-lactam antibiotic tabtoxin in Pseudomonas syringae. J Antibiot (Tokyo) 2006; 58:817-21. [PMID: 16506699 DOI: 10.1038/ja.2005.109] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
DNA sequence analysis revealed that the biosynthetic genes of the unusual beta-lactam antibiotic tabtoxin reside at the att site adjacent to the lysC tRNA gene in Pseudomonas syringae BR2. ORFs encoded within the region included ones with similarity to beta-lactam synthase and clavaminic acid synthase, as well as amino acid synthesis enzymes. Novel ORFs were present in a portion of the biosynthetic region associated with a toxin hypersensitivity phenotype. Tabtoxin resistance was associated with a fragment containing a major facilitator superfamily (MFS) transporter gene.
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Affiliation(s)
- Thomas G Kinscherf
- USDA/ARS Vegetable Crops Research Unit and Department of Plant Pathology, University of Wisconsin - Madison, Madison, WI 53706, USA
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20
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Giotta L, Agostiano A, Italiano F, Milano F, Trotta M. Heavy metal ion influence on the photosynthetic growth of Rhodobacter sphaeroides. CHEMOSPHERE 2006; 62:1490-9. [PMID: 16081134 DOI: 10.1016/j.chemosphere.2005.06.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2005] [Revised: 05/31/2005] [Accepted: 06/12/2005] [Indexed: 05/03/2023]
Abstract
The potential of purple non-sulphur bacteria for bioremediation was assessed by investigating the ability of Rhodobacter sphaeroides strain R26.1 to grow photosynthetically in heavy metal contaminated environments. Bacterial cultures were carried out in artificially polluted media, enriched with the transition metal ions Hg2+, Cu2+, Fe2+, Ni2+, Co2+, MoO4(2-), and CrO4(2-) in millimolar concentration range. For each investigated ion the effect on growth parameters was evaluated. The analysis of concentration-effect curves revealed a differentiated response, indicating that diverse mechanisms of tolerance and/or resistance are involved. Adaptation or selection procedures were not applied, leading to assess intrinsic abilities of coping with these contaminants. The microorganism proved to be highly tolerant to heavy metal exposure, especially towards Co2+, Fe2+ and MoO4(2-). In addition Ni2+ and Co2+ were found to decrease the cellular content of light harvesting complexes. A characteristic behavior was observed with mercuric ions, which produced a significant increase of the lag-phase.
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Affiliation(s)
- Livia Giotta
- Dipartimento di Scienza dei Materiali, Università degli Studi di Lecce, strada per Arnesano, 73100 Lecce, Italy.
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21
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22
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Onyido I, Norris AR, Buncel E. Biomolecule--mercury interactions: modalities of DNA base--mercury binding mechanisms. Remediation strategies. Chem Rev 2005; 104:5911-29. [PMID: 15584692 DOI: 10.1021/cr030443w] [Citation(s) in RCA: 311] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ikenna Onyido
- Department of Chemistry and Center for Agrochemical Technology, University of Agriculture, Makurdi, Nigeria
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23
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Barkay T, Wagner-Döbler I. Microbial Transformations of Mercury: Potentials, Challenges, and Achievements in Controlling Mercury Toxicity in the Environment. ADVANCES IN APPLIED MICROBIOLOGY 2005; 57:1-52. [PMID: 16002008 DOI: 10.1016/s0065-2164(05)57001-1] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Tamar Barkay
- Department of Biochemistry and Microbiology, Cook College, Rutgers University, New Brunswick, New Jersey 08901, USA.
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25
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Abstract
Engineering bacteria for measuring chemicals of environmental or toxicological concern (bioreporter bacteria) has grown slowly into a mature research area. Despite many potential advantages, current bioreporters do not perform well enough to comply with environmental detection standards. Basically, the reasons for this are the lack of engineering principles in the detection chain in the bioreporters. Here, we dissect critical steps in the detection chain and illustrate how bioreporter design could be improved by mutagenizing specificity and selectivity of the sensing and regulatory proteins, by newer expression strategies and application of different signalling networks. Furthermore, we describe how redesigning bioreporter assays with respect to pollutant transport into the cells and application of other detection devices can decrease detection limits and increase the speed of detection.
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Affiliation(s)
- Jan Roelof van der Meer
- Department of Fundamental Microbiology, Bâtiment de Biologie, University of Lausanne, 1015 Lausanne, Switzerland.
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26
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Rossy E, Sénèque O, Lascoux D, Lemaire D, Crouzy S, Delangle P, Covès J. Is the cytoplasmic loop of MerT, the mercuric ion transport protein, involved in mercury transfer to the mercuric reductase? FEBS Lett 2004; 575:86-90. [PMID: 15388338 DOI: 10.1016/j.febslet.2004.08.041] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2004] [Revised: 08/12/2004] [Accepted: 08/16/2004] [Indexed: 11/17/2022]
Abstract
In MerT, the mercury transporter, a first cysteine pair, located in the first trans-membrane helix, receives mercury from the periplasm. Then, a second cysteine pair, housed in a cytoplasmic loop connecting the second and the third trans-membrane helices, is thought to transfer the metal to another cysteine pair located in the N-terminal extension of the mercuric reductase. We found that a 23-amino acid synthetic peptide corresponding to the cytoplasmic loop can bind one mercury atom per molecule and that this mercury atom can be transferred specifically to MerAa. The solution structure of Hg-bound ppMerT has been solved by 1H NMR spectroscopy.
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Affiliation(s)
- Emmanuel Rossy
- Laboratoire de Chimie et Biochimie des Centres Redox Biologiques, DRDC/CB, CEA-Grenoble, France
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27
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Serre L, Rossy E, Pebay-Peyroula E, Cohen-Addad C, Covès J. Crystal Structure of the Oxidized Form of the Periplasmic Mercury-binding Protein MerP from Ralstonia metallidurans CH34. J Mol Biol 2004; 339:161-71. [PMID: 15123428 DOI: 10.1016/j.jmb.2004.03.022] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2003] [Revised: 01/23/2004] [Accepted: 03/12/2004] [Indexed: 11/27/2022]
Abstract
In Ralstonia metallidurans CH34, the gene merP encodes for a periplasmic mercury-binding protein which is capable of binding one mercury atom. The metal-binding site of MerP consists of the highly conserved sequence GMTCXXC found in the family that includes metallochaperones and metal-transporting ATPases. We purified MerP from R.metallidurans CH34 and solved its crystal structure under the oxidized form at 2.0A resolution. Superposition with structures of other metal-binding proteins shows that the global structure of R.metallidurans CH34 oxidized MerP follows the general topology of the whole family. The largest differences are observed with the NMR structure of oxidized Shigella flexneri MerP. Detailed analysis of the metal-binding site suggests a direct role for Y66 in stabilizing the thiolate group of C17 during the mercury-binding reaction. The metal-binding site of oxidized MerP is also similar to the metal-binding sites of oxidized copper chaperone for superoxide dismutase and Atx1, two copper-binding proteins from Saccharomyces cerevisiae. Finally, the packing of the MerP crystals suggests that F38, a well-conserved residue in the MerP family may be important in mercury binding and transfer. We propose a possible mechanism of mercury transfer between two CXXC motifs based on a transient bi-coordinated mercury intermediate.
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Affiliation(s)
- Laurence Serre
- Institut de Biologie Structurale, UMR 5075-CNRS-CEA-UJF/ IBS-LPM, 41 Avenue Jules Horowitz, 38027 Grenoble Cedex 01, France.
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28
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Rossy E, Champier L, Bersch B, Brutscher B, Blackledge M, Covès J. Biophysical characterization of the MerP-like amino-terminal extension of the mercuric reductase from Ralstonia metallidurans CH34. J Biol Inorg Chem 2003; 9:49-58. [PMID: 14624351 DOI: 10.1007/s00775-003-0495-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2003] [Accepted: 09/26/2003] [Indexed: 10/26/2022]
Abstract
The purified native mercuric reductase (MerA) from Ralstonia metallidurans CH34 contains an N-terminal sequence of 68 amino acids predicted to be homologous to MerP, the periplasmic mercury-binding protein. This MerP-like protein has now been expressed independently. The protein was named MerAa by homology with Ccc2a, the first soluble domain of the copper-transporting ATPase from yeast. Deltaa has been characterized using a set of biophysical techniques. The binding of mercury was followed using circular dichroism spectroscopy and electrospray mass spectrometry. The two cysteine residues contained in the consensus sequence GMTC XXC are involved in the binding of one mercury atom, with an apparent affinity comparable to that of MerP for the same metal. The metal-binding site is confirmed by NMR chemical shift changes observed between apo- and metal-bound MerAa in solution. NMR shift and NOE data also indicate that only minor structural changes occur upon metal binding. Further NMR investigation of the fold of MerAa using long-range methyl-methyl NOE and backbone residual dipolar coupling data confirm the expected close structural homology with MerP. (15)N relaxation data show that MerAa is a globally rigid molecule. An increased backbone mobility was observed for the loop region connecting the first beta-strand and the first alpha-helix and comprising the metal-binding domain. Although significantly reduced, this loop region keeps some conformational flexibility upon metal binding. Altogether, our data suggest a role of MerAa in mercury trafficking.
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Affiliation(s)
- Emmanuel Rossy
- Laboratoire de Chimie et Biochimie des Centres Redox Biologiques, CEA-Grenoble, DRDC/CB, UMR 5047 CNRS - CEA, Université Joseph Fourier, 17 Avenue des Martyrs, 38054 Cedex 9, Grenoble, France
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29
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Abstract
Bacterial resistance to inorganic and organic mercury compounds (HgR) is one of the most widely observed phenotypes in eubacteria. Loci conferring HgR in Gram-positive or Gram-negative bacteria typically have at minimum a mercuric reductase enzyme (MerA) that reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic Hg(0) vapor and a membrane-bound protein (MerT) for uptake of Hg(II) arranged in an operon under control of MerR, a novel metal-responsive regulator. Many HgR loci encode an additional enzyme, MerB, that degrades organomercurials by protonolysis, and one or more additional proteins apparently involved in transport. Genes conferring HgR occur on chromosomes, plasmids, and transposons and their operon arrangements can be quite diverse, frequently involving duplications of the above noted structural genes, several of which are modular themselves. How this very mobile and plastic suite of proteins protects host cells from this pervasive toxic metal, what roles it has in the biogeochemical cycling of Hg, and how it has been employed in ameliorating environmental contamination are the subjects of this review.
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Affiliation(s)
- Tamar Barkay
- Department of Biochemistry and Microbiology, Cook College, Rutgers University, New Brunswick, NJ, USA.
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