Detoxification of mercury and organomercurials by nitrogen-fixing soil bacteria
TL;DR: Minimal inhibitory concentration values of HgCl2 and 5 organomercurials were determined against 24 mercury-resistant N2-fixing soil bacteria previously isolated from soil and identified in the laboratory.
Abstract: Minimal inhibitory concentration values of HgCl2 and 5 organomercurials were determined against 24 mercury-resistant N2-fixing soil bacteria previously isolated from soil and identified in our laboratory. These bacterial strains also displayed multiple antibiotic resistant properties. Typical growth pattern of a highly mercury-resistantBeijerinckia sp (KDr2) was studied in liquid broth supplemented with toxic levels of mercury compounds. Four bacterial strains were selected for determining their ability to volatilize mercury and their Hg-volatilizing capacity was different. Cell-free extracts prepared from overnight mercury-induced cells catalyzed Hg2+-induced NADPH oxidation. Specific activities of Hg2+-reductase which is capable of catalyzing conversion of Hg2+ →Hg(o) of 10 Hg-resistant bacterial strains are also reported.
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TL;DR: This is the first study to use an IncP-1β plasmid directly isolated from the environment, to generate a novel and stable bacterial strain useful for mercury bioremediation.
Abstract: Background
Mercury-polluted environments are often contaminated with other heavy metals. Therefore, bacteria with resistance to several heavy metals may be useful for bioremediation. Cupriavidus metallidurans CH34 is a model heavy metal-resistant bacterium, but possesses a low resistance to mercury compounds.
92 citations
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TL;DR: Levels of merA-specific mRNA and Hg(II) volatilization were influenced more by microbial metabolic activity than by the concentration of mercury, suggesting that rates of mercury volatiles in environmental samples may not always be proportional to merA expression.
Abstract: The relationship of merA gene expression (specifying the enzyme mercuric reductase) to mercury volatilization in aquatic microbial communities was investigated with samples collected at a mercury-contaminated freshwater pond, Reality Lake, in Oak Ridge, Tenn. Levels of merA mRNA transcripts and the rate of inorganic mercury [Hg(II)] volatilization were related to the concentration of mercury in the water and to heterotrophic activity in field samples and laboratory incubations of pond water in which microbial heterotrophic activity and Hg(II) concentration were manipulated. Levels of merA-specific mRNA and Hg(II) volatilization were influenced more by microbial metabolic activity than by the concentration of mercury. merA-specific transcripts were detected in some samples which did not reduce Hg(II), suggesting that rates of mercury volatilization in environmental samples may not always be proportional to merA expression.
78 citations
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TL;DR: Levels of merA-specific transcripts and Hg(II) volatilization were influenced more by microbial activity (as manipulated by nutrient additions) than by the concentration of total mercury, suggesting that rates of mercury vol atilization in the environment may not always be proportional to merA transcription.
Abstract: Bacterial transformation of mercury in the environment has received much attention owing to the toxicity of both the ionic form and organomercurial compounds. Bacterial resistance to mercury and the role of bacteria in mercury cycling have been widely studied. The genes specifying the required functions for resistance to mercury are organized on the mer operon. Gene probing methodologies have been used for several years to detect specific gene sequences in the environment that are homologous to cloned mer genes. While mer genes have been detected in a wide variety of environments, less is known about the expression of these genes under environmental conditions. We combined new methodologies for recovering specific gene mRNA transcripts and mercury detection with a previously described method for determining biological potential for mercury volatilization to examine the effect of mercury concentrations and nutrient availability on rates of mercury volatilization and merA transcription. Levels of merA-specific transcripts and Hg(II) volatilization were influenced more by microbial activity (as manipulated by nutrient additions) than by the concentration of total mercury. The detection of merA-specific transcripts in some samples that did not reduce Hg(II) suggests that rates of mercury volatilization in the environment may not always be proportional to merA transcription.
41 citations
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TL;DR: Cell-free extracts prepared from narrow-spectrum Hg-resistant bacterial strains induced by HgCl(2) exhibited Hg(+2)-dependent NADPH oxidation, indicating the presence of only mercuric reductase enzyme.
Abstract: Mercury-resistant bacteria belonging to the genera Bacillus, Escherichia, Klebsiella, Micrococcus, Pseudomonas, Salmonella, Sarcina, Shigella, Staphylococcus and Streptococcus were isolated from gills and guts of fresh water fish collected from wetland fisheries around Calcutta, India, contaminated with mercury compounds. The total number of bacteria, as well as Hg-resistant bacteria, were always higher in guts than gills. Bottom-dwelling fish contained higher number of bacteria, including Hg-resistant bacteria, than surface and middle water dwelling fish. They belonged either to narrow-spectrum or to broad-spectrum Hg-resistant groups and they also possessed other heavy metal and antibiotic resistant properties. In the presence of toxic levels of HgCl2, phenylmercuric acetate (PMA) and methylmercuric chloride (MMC), the lag in growth of the bacterial strains gradually increased with increasing concentration of Hg-compounds. Narrow-spectrum Hg-resistant bacterial strains volatilized only HgCl2 from the liquid medium in the range of 64–89%, whereas the broad-spectrum group exhibited a high level of HgCl2 (80–94%), PMA (72–84%) and MMC (64–80%) volatilizing capacity with inducible mercuric reductase and organomercurial lyase enzyme activities in their cell-free extracts. Cell-free extracts prepared from narrow-spectrum Hg-resistant bacterial strains induced by HgCl2 exhibited Hg+2-dependent NADPH oxidation, indicating the presence of only mercuric reductase enzyme.
32 citations
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TL;DR: In this paper, the authors highlight the role of these bacterial consortia in self-cleaning and bioremediation of environments contaminated with oil and mercury, and demonstrate that these bacteria make them self-sufficient in terms of their nitrogen nutrition.
Abstract: Pristine and oil-polluted coastal and desert soil samples from Kuwait contained between about 1.0 × 10 7 and 2.5 × 10 8 colony-forming units (CFU) g −1 of bacteria with the combined potential for hydrocarbon utilization, nitrogen fixation, and Hg 2+ resistance and volatilization. Soils with a long history of oil pollution were richest in these bacteria, and contained strains with the highest resistance to mercury. In the presence of oil, mercury resistance by the studied predominant strains decreased, but strains from oily desert soils could still resist up to 80 ppm HgCl 2 in the presence of oil. The oil-attenuation potential of predominant strains in culture was also inhibited by HgCl 2 . However, satisfactory oil-attenuation rates still occurred in culture in the presence of up to 400 ppm of HgCl 2 . The diazotrophic potential of these bacteria makes them self-sufficient, as far as their nitrogen nutrition is concerned. These findings highlight the role of these bacterial consortia in self-cleaning and bioremediation of environments contaminated with oil and mercury.
27 citations
References
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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
1,113 citations
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TL;DR: The mercury cycle in the biosphere and biological methylation of mercury and microbial resistance to mercury and organomercurials are studied.
Abstract: BIOTRANSFORMA nONS OF TOXIC MET AL CAnONS . Mercury . The mercury cycle in the biosphere .. Biological methylation of mercury . Microbial resistance to mercury and organomercurials .
409 citations
"Detoxification of mercury and organ..." refers background in this paper
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TL;DR: Two separate enzymes, which determine resistance to inorganic mercury and organomercurials, have been purified from the plasmid-bearing Escherichia coli strain J53-1(R831), suggesting that the native enzyme is composed of three identical subunits.
Abstract: Two separate enzymes, which determine resistance to inorganic mercury and organomercurials, have been purified from the plasmid-bearing Escherichia coli strain J53-1(R831). The mercuric reductase that reduces Hg2+ to volatile Hg0 was purified about 240-fold from the 160,000 X g supernatant of French press disrupted cells. This enzyme contains bound FAD, requires NADPH as an electron donor, and requires the presence of a sulfhydryl compound for activity. The reductase has a Km of 13 micron HgCl2, a pH optimum of 7.5 in 50 mM sodium phosphate buffer, an isoelectric point of 5.3, a Stokes radius of 50 A, and a molecular weight of about 180,000. The subunit molecular weight, determined by gel electrophoresis in the presence of sodium dodecyl sulfate, is about 63,000 +/- 2,000. These results suggest that the native enzyme is composed of three identical subunits. The organomercurial hydrolase, which breaks the mercury-carbon bond in compounds such as methylmercuric chloride, phenylmercuric acetate, and ethylmercuric chloride, was purified about 38-fold over the starting material. This enzyme has a Km of 0.56 micron for ethylmercuric chloride, a Km of 7.7 micron for methylmercuric chloride, and two Km values of 0.24 micron and over 200 micron for phenylmercuric acetate. The hydrolase has an isoelectric point of 5.5, requires the presence of EDTA and a sulfhydryl compound for activity, has a Stokes radius of 24 A, and has a molecular weight of about 43,000 +/- 4,000.
195 citations
"Detoxification of mercury and organ..." refers background in this paper
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TL;DR: A strain of Escherichia coli carrying genes determining mercury resistance on a naturally occurring resistance transfer factor (RTF) converts 95% of 10(-5)m Hg(2+) (chloride) to metallic mercury at a rate of 4 to 5 nmoles of Hg (2+) per min per 10(8) cells.
Abstract: A strain of Escherichia coli carrying genes determining mercury resistance on a naturally occurring resistance transfer factor (RTF) converts 95% of 10−5m Hg2+ (chloride) to metallic mercury at a rate of 4 to 5 nmoles of Hg2+ per min per 108 cells. The metallic mercury is rapidly eliminated from the culture medium as mercury vapor. The volatilizing activity has a temperature dependence and heat sensitivity characteristic of enzymatic catalysis and is inducible by mercuric chloride. Ag+ and Au3+ are markedly inhibitory of mercury volatilization.
192 citations
"Detoxification of mercury and organ..." refers methods in this paper
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