Mechanisms of microbial resistance and detoxification of mercury and organomercury compounds: physiological, biochemical, and genetic analyses.
TL;DR: It is shown that under aerobic conditions, methylmercury formation under Anaerobic conditions and under Aerobic conditions is more stable than under either of the other conditions.
Abstract: METHYLATION OF MERCURY BY MICROORGANISMS ..................................... 96 Mechanism of Methylation of Mercury....................................................... 96 Methylmercury Formation Under Anaerobic Conditions ........................................ 97 Methylmercury Formation Under Aerobic Conditions .......................................... 97 Effects of HgS on Methylation of Mercury .......... .......................................... 98
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TL;DR: The current state of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its transformation into highly toxic methylated forms is examined in this paper.
Abstract: Mercury is one of the most hazardous contaminants that may be present in the aquatic environment, but its ecological and toxicological effects are strongly dependent on the chemical species present. Species distribution and transformation processes in natural aquatic systems are controlled by various physical, chemical, and biological factors. Depending on the prevailing environmental conditions, inorganic mercury species may be converted to many times more toxic methylated forms such as methylmercury, a potent neurotoxin that is readily accumulated by aquatic biota. Despite a considerable amount of literature on the subject, the behavior of mercury and many of the transformation and distribution mechanisms operating in the natural aquatic environment are still poorly understood. This review examines the current state of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its transformation into highly toxic methylated forms.
1,481 citations
TL;DR: In this article, the authors applied substrate-electron acceptor combinations and specific metabolic inhibitors to anoxic saltmarsh sediment spiked with mercuric ions (Hg2+) in an effort to identify, by a direct approach, the microorganisms responsible for the synthesis of hazardous monomethylmercury.
Abstract: Substrate-electron acceptor combinations and specific metabolic inhibitors were applied to anoxic saltmarsh sediment spiked with mercuric ions (Hg2+) in an effort to identify, by a direct approach, the microorganisms responsible for the synthesis of hazardous monomethylmercury. 2-Bromoethane sulfonate (30 mM), a specific inhibitor of methanogens, increased monomethylmercury synthesis, whereas sodium molybdate (20 mM), a specific inhibitor of sulfate reducers, decreased Hg2+ methylation by more than 95%. Anaerobic enrichment and isolation procedures yielded a Desulfovibrio desulfuricans culture that vigorously methylated Hg2+ in culture solution and also in samples of presterilized sediment. The Hg2+ methylation activity of sulfate reducers is fully expressed only when sulfate is limiting and fermentable organic substrates are available. To date, sulfate reducers have not been suspected of Hg2+ methylation. Identification of these bacteria as the principal methylators of Hg2+ in anoxic sediments raises questions about the environmental relevance of previous pure culture-based methylation work.
1,195 citations
01 Jan 1987
TL;DR: A review of the available literature on the ecological and toxicological aspects of mercury (Hg) in the environment, with special reference to fish and wildlife resources, is reviewed and summarized in this paper.
Abstract: SUMMARY Available literature on the ecological and toxicological aspects of mercury (Hg) in the environment, with special reference to fish and wildlife resources, is reviewed and summarized. Subdivisions include sources, chemical properties, background concentrations, acute and chronic toxicity, sublethal effects, and proposed criteria to protect sensitive resources. Mercury has been used by man for at least 2,300 years, most recently as a fungicide in agriculture, in the manufacture of chlorine and sodium hydroxide, as a slime control agent in the pulp and paper industry, in the production of plastics and electrical apparatus, and in mining and smelting operations. Mercury burdens in some environmental compartments are estimated to have increased up to 5X precultural levels, primarily as a result of man's activities. The construction of artificial reservoirs, for example, which releases Hg from flooded soils, has contributed to the observed elevation of Hg concentrations in fish tissues from these localities. Elevated levels of Hg in living organisms in Hg-contaminated areas may persist for as long as 100 years after the source of pollution has been discontinued. One major consequence of increased mercury use, coupled with careless waste disposal practices, has been a sharp increase in the number of epidemics of fatal mercury poisonings in humans, wildlife, and aquatic organisms. Most authorities agree on six points: (1) mercury and its compounds have no known biological function, and the presence of the metal in the cells of living organisms is undesirable and potentially hazardous; (2) forms of mercury with relatively low toxicity can be transformed into forms of very high toxicity, such as methylmercury, through biological and other processes; (3) mercury can be bioconcentrated in organisms and biomagnified through food chains; (4) mercury is a mutagen, teratogen, and carcinogen, and causes embryocidal, cytochemical, and histopathological effects; (5) some species of fish and wildlife contain high concentrations of Hg that are not attributable to human activities; (6) anthropogenic use of Hg should be curtailed, as the difference between tolerable natural background levels of Hg and harmful effects in the environment is exceptionally small. Concentrations of total Hg lethal to sensitive, representative, nonhuman species range from 0.1 to 2.0 ug/l (ppb) of medium for aquatic organisms; from 2,200 to 31,000 ug/kg body weight (acute oral) and 4,000 to 40,000 ug/kg (dietary) for birds; and from 100 to 500 ug/kg body weight (daily dose) and 1,000 to 5,000 ug/kg diet for mammals. Organomercury compounds, especially methylmercury, …
1,135 citations
TL;DR: Microorganisms can enzymatically reduce a variety of metals in metabolic processes that are not related to metal assimilation, including technetium, vanadium, molybdenum, gold, silver, and copper, but reduction of these metals has not been studied extensively.
Abstract: Microorganisms can enzymatically reduce a variety of metals in metabolic processes that are not related to metal assimilation. Some microorganisms can conserve energy to support growth by coupling the oxidation of simple organic acids and alcohols, H2, or aromatic compounds to the reduction of Fe(III) or Mn(IV). This dissimilatory Fe(III) and Mn(IV) reduction influences the organic as well as the inorganic geochemistry of anaerobic aquatic sediments and ground water. Microorganisms that use U(VI) as a terminal electron acceptor play an important role in uranium geochemistry and may be a useful tool for removing uranium from contaminated environments. Se(VI) serves as a terminal electron acceptor to support anaerobic growth of some microorganisms. Reduction of Se(VI) to Se(O) is an important mechanism for the precipitation of selenium from contaminated waters. Enzymatic reduction of Cr(VI) to the less mobile and less toxic Cr(III), and reduction of soluble Hg(II) to volatile Hg(O) may affect the fate of these compounds in the environment and might be used as a remediation strategy. Microorganisms can also enzymatically reduce other metals such as technetium, vanadium, molybdenum, gold, silver, and copper, but reduction of these metals has not been studied extensively.
988 citations
908 citations
References
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Book•
01 Jan 2007
TL;DR: Handbook of the Toxicology of Metals as discussed by the authors is the standard reference work for physicians, toxicologists and engineers in the field of environmental and occupational health, which is a comprehensive review of the effects on biological systems from metallic elements and compounds.
Abstract: "Handbook of the Toxicology of Metals" is the standard reference work for physicians, toxicologists and engineers in the field of environmental and occupational health. This new edition is a comprehensive review of the effects on biological systems from metallic elements and their compounds. An entirely new structure and illustrations represent the vast array of advancements made since the last edition. Special emphasis has been placed on the toxic effects in humans with chapters on the diagnosis, treatment and prevention of metal poisoning.This up-to-date reference provides easy access to a broad range of basic toxicological data and also gives a general introduction to the toxicology of metallic compounds. It covers up-to-date toxicological information on 31 metallic elements and their compounds, each in a separate chapter. It includes new chapters on general chemistry, biological monitoring and biomarkers, essential metals, principles for prevention of the toxic effects of metals, and more.
2,967 citations
TL;DR: In this paper, an extremely sensitive and accurate method for the detn. of Hg down to 1.0 ppb has been described and applied to Ni and Co metal as well as rock samples and soil samples contg. materials.
Abstract: The procedure outlined describes an extremely sensitive and accurate method for the detn. of Hg down to 1.0 ppb. in soln. This procedure has been applied to Ni and Co metal as well as rock samples and soil samples contg. org. materials. The sample is taken into soln. by an oxidizing acid attack. Hg is then reduced to the elemental state and aerated from soln. in a closed system. The Hg vapor passes through a quartz absorption cell of an at. absorption spectrophotometer where its concn. is measured. The proceure is free from interferences due to org. matter or other volatile constituents of the sam ple. Large amts. of easily reducible elements must be absent from -- AATA
1,122 citations
"Mechanisms of microbial resistance ..." refers background in this paper
...tion to Hg0 of the remaining mercury compounds (38)....
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TL;DR: It is reported that both mono and dimethylmercury can be produced in bottom sediments and in rotten fish, and relate the findings to the hazards of mercury pollution.
Abstract: FRESHWATER fish, especially pike (Esox lucius), from Sweden sometimes contain abnormally large amounts of mercury1. It was initially concluded to be either inorganic mercury or phenyl mercury, which are known to be released as industrial wastes, but later it was shown that the mercury was present almost entirely as methyl mercury (CH3Hg+)2. A possible explanation is that living organisms have the capacity to methylate mercury compounds present in pollution. We now report that both mono and dimethylmercury (CH3Hg+ and CH3HgCH3) can be produced in bottom sediments and in rotten fish, and relate the findings to the hazards of mercury pollution.
865 citations
"Mechanisms of microbial resistance ..." refers background in this paper
...lytically modified form of the 69-kdal polypeptide (47)....
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...The biological methylation of mercury has been demonstrated under anaerobic conditions by bacteria in river and lake sediments and rotting fish, as well as by cell-free extracts of methanogenic bacteria (47, 78, 124-127)....
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...Bottom sediments from freshwater aquaria and putrescent homogenates of fish have been shown to produce methylmercury from Hg2+ and dimethylmercury from methylmercury, respectively (47)....
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...The methylation of mercury by microorganisms from soil, sediments, and even the human intestinal tract has been reported (26, 47, 48, 122, 124, 125)....
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TL;DR: The environmental and microbiological factors that can influence heavy metal toxicity are discussed with a view to understanding the mechanisms of microbial metal tolerance.
Abstract: The environmental and microbiological factors that can influence heavy metal toxicity are discussed with a view to understanding the mechanisms of microbial metal tolerance. It is apparent that metal toxicity can be heavily influenced by environmental conditions. Binding of metals to organic materials, precipitation, complexation, and ionic interactions are all important phenomena that must be considered carefully in laboratory and field studies. It is also obvious that microbes possess a range of tolerance mechanisms, most featuring some kind of detoxification. Many of these detoxification mechanisms occur widely in the microbial world and are not only specific to microbes growing in metal-contaminated environments.
710 citations
707 citations
"Mechanisms of microbial resistance ..." refers background in this paper
...It is generally accepted that these elements play an important role in evolution (53)....
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...These elements have demonstrated the ability to transpose from plasmid to plasmid and from plasmid to chromosome, carrying genes for antibiotic resistance, as well as a variety of functions including fusion of unrelated DNA molecules, deletions, inversions, excisions, and as functional transcriptional start and stop signals (53)....
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