Determination of the spatial characteristics of an RF electrodeless discharge by the method of emission tomography

The spatial distribution of the density of mercury atoms in the 7³ S state in a spherical RF electrode-less gas-discharge lamp is reconstructed by the method of emission tomography. The local values of the corresponding emission coefficients, which are proportional to the density of mercury atoms in the 7³ S state, are determined from integral (over the plasma volume) measurements of the lamp radiation at a wavelength of 546.1 nm with the help of an algorithm based on the maximum entropy method. The results obtained show that, for all of the operating modes under study, the profile of the density of mercury atoms in the 7³ S state has a minimum in the center of the lamp and a maximum near its wall. At a generator current of 100 mA and cold-spot temperature of 41°C, the density of mercury atoms in the 7³ S state is observed to drop substantially both in the center of the lamp and near its wall, the density in the center being reduced to almost zero. An explanation of this phenomenon is proposed.     

Mercury Methylation by Desulfovibrio desulfuricans ND132 in the Presence of Polysulfides

The extracellular speciation of mercury may control bacterial uptake and methylation. Mercury-polysulfide complexes have recently been shown to be prevalent in sulfidic waters containing zero-valent sulfur. Despite substantial increases in total dissolved mercury concentration, methylation rates in cultures of Desulfovibrio desulfuricans ND132 equilibrated with cinnabar did not increase in the presence of polysulfides, as expected due to the large size and charged nature of most of the complexes. In natural waters not at saturation with cinnabar, mercury-polysulfide complexes would be expected to shift the speciation of mercury from HgS⁰_(aq) toward charged complexes, thereby decreasing methylation rates.     

The Use of a Mercury Biosensor to Evaluate the Bioavailability of Mercury-Thiol Complexes and Mechanisms of Mercury Uptake in Bacteria

As mercury (Hg) biosensors are sensitive to only intracellular Hg, they are useful in the investigation of Hg uptake mechanisms and the effects of speciation on Hg bioavailability to microbes. In this study, bacterial biosensors were used to evaluate the roles that several transporters such as the glutathione, cystine/cysteine, and Mer transporters play in the uptake of Hg from Hg-thiol complexes by comparing uptake rates in strains with functioning transport systems to strains where these transporters had been knocked out by deletion of key genes. The Hg uptake into the biosensors was quantified based on the intracellular conversion of inorganic mercury (Hg(II)) to elemental mercury (Hg(0)) by the enzyme MerA. It was found that uptake of Hg from Hg-cysteine (Hg(CYS)₂) and Hg-glutathione (Hg(GSH)₂) complexes occurred at the same rate as that of inorganic complexes of Hg(II) into Escherichia coli strains with and without intact Mer transport systems. However, higher rates of Hg uptake were observed in the strain with a functioning Mer transport system. These results demonstrate that thiol-bound Hg is bioavailable to E. coli and that this bioavailability is higher in Hg-resistant bacteria with a complete Mer system than in non-resistant strains. No difference in the uptake rate of Hg from Hg(GSH)₂ was observed in E. coli strains with or without functioning glutathione transport systems. There was also no difference in uptake rates between a wildtype Bacillus subtilis strain with a functioning cystine/cysteine transport system, and a mutant strain where this transport system had been knocked out. These results cast doubt on the viability of the hypothesis that the entire Hg-thiol complex is taken up into the cell by a thiol transporter. It is more likely that the Hg in the Hg-thiol complex is transferred to a transport protein on the cell membrane and is subsequently internalized.     

Mercury Concentrations in Common Tern Sterna hirundo and Slender-billed Gull Larus genei from the Shadegan Marshes of Iran,in North-western Corner of the Persian Gulf

We examined mercury levels in several tissues of Common Terns and Slender-billed Gulls collected from Shadegan Marshes of south-western Iran. In both species, total mercury content was highest in feathers followed by liver, kidney and muscle tissue. We found a significant correlation between mercury concentrations in kidney and breast feather (r?=?0.83, p?<?0.05), breast feather and liver (r?=?0.81, p?<?0.05) as well as liver and kidney (r?=?0.83, p?<?0.05). The contaminant levels in the feathers (11.53 and 15.32 μg/g in breast feather and tail feather, respectively) of Common Terns from Shadegan Marshes are higher than those reported for other tern species from elsewhere in the world, but feather mercury of Slender-billed Gull (6.61 and 5.35 μg/g in breast feather and tail feather, respectively) was similar to those reported for gull species worldwide. Mean values for mercury in the feather of two seabird species were higher than the levels known to cause adverse effects.     

Syntrophs Dominate Sequences Associated with the Mercury Methylation-Related Gene hgcA in the Water Conservation Areas of the Florida Everglades

The mechanisms and rates of mercury methylation in the Florida Everglades are of great concern because of potential adverse impacts on human and wildlife health through mercury accumulation in aquatic food webs. We developed a new PCR primer set targeting hgcA, a gene encoding a corrinoid protein essential for Hg methylation across broad phylogenetic boundaries, and used this primer set to study the distribution of hgcA sequences in soils collected from three sites along a gradient in sulfate and nutrient concentrations in the northern Everglades. The sequences obtained were distributed in diverse phyla, including Proteobacteria, Chloroflexi, Firmicutes, and Methanomicrobia; however, hgcA clone libraries from all sites were dominated by sequences clustering within the order Syntrophobacterales of the Deltaproteobacteria (49 to 65% of total sequences). dsrB mRNA sequences, representing active sulfate-reducing prokaryotes at the time of sampling, obtained from these sites were also dominated by Syntrophobacterales (75 to 89%). Laboratory incubations with soils taken from the site low in sulfate concentrations also suggested that Hg methylation activities were primarily mediated by members of the order Syntrophobacterales, with some contribution by methanogens, Chloroflexi, iron-reducing Geobacter, and non-sulfate-reducing Firmicutes inhabiting the sites. This suggests that prokaryotes distributed within clades defined by syntrophs are the predominant group controlling methylation of Hg in low-sulfate areas of the Everglades. Any strategy for managing mercury methylation in the Everglades should consider that net mercury methylation is not limited to the action of sulfate reduction.     

Bioaccumulation of Trace Mercury in Trophic Levels of Benthic, Benthopelagic, Pelagic Fish Species, and Sea Birds from Arvand River, Iran

In this study, concentration of mercury was determined in the trophic levels of benthic, benthopelagic, pelagic fish species, and river birds from Arvand River, located in the Khuzestan province in the lowlands of southwestern Iran at the head of the Persian Gulf. The order of mercury concentrations in tissues of the fish species was as follows: liver>gill>muscle and in tissues of the kingfisher species was as follows: feather>liver>kidney>muscle. Therefore, liver in fish and feather in kingfisher exhibited higher mercury concentration than the other tissues. There was a positive correlation between mercury concentrations in fish and kingfisher species with size of its food items. We expected to see higher mercury levels in tissues of female species because they are larger and can eat larger food items. The results of this study show that the highest mean mercury level were found in the kingfisher (Anas crecca), followed by benthic (Epinephelus diacanthus), benthopelagic (Chanos chanos), and pelagic fish (Strongylura strongylura). Mean value of mercury in fish species, S. strongylura were (0.61 μg g^?1 dry weight), C. chanos (0.45 μg g^?1 dry weight), E. diacanthus (0.87 μg g^?1 dry weight), and in kingfisher species A. crecca was (2.64 μg g^?1 dry weight). Significant correlation between mercury concentration in fish and kingfisher may be related to high variability of mercury in the fish.     

Optical characteristics and parameters of gas-discharge plasma in a mixture of mercury dibromide vapor with neon

Results are presented from studies of the optical characteristics and parameters of plasma of a dielectric barrier discharge in a mixture of mercury dibromide vapor with neon—the working medium of a non-coaxial exciplex gas-discharge emitter. The electron energy distribution function, the transport characteristics, the specific power losses for electron processes, the electron density and temperature, and the rate constants for the processes of elastic and inelastic electron scattering by the working mixture components are determined as functions of the reduced electric field. The rate constant of the process leading to the formation of exciplex mercury monobromide molecules is found to be 1.6 × 10^?14 m³/s for a reduced electric field of E/N = 15 Td, at which the maximum emission intensity in the blue-green spectral region (λ_max = 502 nm) was observed in this experiment.     

Staphylococcus aureus - induced tumor necrosis factor - related apoptosis - inducing ligand expression mediates apoptosis and caspase-8 activation in infected osteoblasts

Background

Bacterial mercury resistance is based on enzymatic reduction of ionic mercury to elemental mercury and has recently been demonstrated to be applicable for industrial wastewater clean-up. The long-term monitoring of such biocatalyser systems requires a cultivation independent functional community profiling method targeting the key enzyme of the process, themerAgene coding for the mercuric reductase. We report on the development of a profiling method formerAand its application to monitor changes in the functional diversity of the biofilm community of a technical scale biocatalyzer over 8 months of on-site operation.

Results

Based on an alignment of 30merAsequences from Gram negative bacteria, conserved primers were designed for amplification ofmerAfragments with an optimized PCR protocol. The resulting amplicons of approximately 280 bp were separated by thermogradient gelelectrophoresis (TGGE), resulting in strain specific fingerprints for mercury resistant Gram negative isolates with differentmerAsequences. ThemerAprofiling of the biofilm community from a technical biocatalyzer showed persistence of some and loss of other inoculum strains as well as the appearance of new bands, resulting in an overall increase of the functional diversity of the biofilm community. One predominant new band of themerAcommunity profile was also detected in a biocatalyzer effluent isolate, which was identified asPseudomonas aeruginosa. The isolated strain showed lower mercury reduction rates in liquid culture than the inoculum strains but was apparently highly competitive in the biofilm environment of the biocatalyzer where moderate mercury levels were prevailing.

Conclusions

ThemerAprofiling technique allowed to monitor the ongoing selection for better adapted strains during the operation of a biocatalyzer and to direct their subsequent isolation. In such a way, a predominant mercury reducingPs. aeruginosastrain was identified by its unique mercuric reductase gene.     

Seafood Substitutions Obscure Patterns of Mercury Contamination in Patagonian Toothfish (Dissostichus eleginoides) or “Chilean Sea Bass”

Seafood mislabeling distorts the true abundance of fish in the sea, defrauds consumers, and can also cause unwanted exposure to harmful pollutants. By combining genetic data with analyses of total mercury content, we have investigated how species substitutions and fishery-stock substitutions obscure mercury contamination in Patagonian toothfish (Dissostichus eleginoides), also known as “Chilean sea bass”. Patagonian toothfish show wide variation in mercury concentrations such that consumers may be exposed to either acceptable or unacceptable levels of mercury depending on the geographic origins of the fish and the allowable limits of different countries. Most notably, stocks of Patagonian toothfish in Chile accumulate significantly more mercury than stocks closer to the South Pole, including the South Georgia/Shag Rocks stock, a fishery certified by the Marine Stewardship Council (MSC) as sustainably fished. Consistent with the documented geography of mercury contamination, our analysis showed that, on average, retail fish labeled as MSC-certified Patagonian toothfish had only half the mercury of uncertified fish. However, consideration of genetic data that were informative about seafood substitutions revealed a complex pattern of contamination hidden from consumers: species substitutions artificially inflated the expected difference in mercury levels between MSC-certified and uncertified fish whereas fishery stock substitutions artificially reduced the expected difference in mercury content between MSC-certified and uncertified fish that were actually D. eleginoides. Among MSC-certified fish that were actually D. eleginoides, several with exogenous mtDNA haplotypes (i.e., not known from the certified fishery) had mercury concentrations on par with uncertified fish from Chile. Overall, our analysis of mercury was consistent with inferences from the genetic data about the geographic origins of the fish, demonstrated the potential negative impact of seafood mislabeling on unwanted mercury exposure for consumers, and showed that fishery-stock substitutions may expose consumers to significantly greater mercury concentrations in retail-acquired fish than species substitutions.     

Mercury in Nelson's Sparrow subspecies at breeding sites

Background

Mercury is a persistent, biomagnifying contaminant that can cause negative effects on ecosystems. Marshes are often areas of relatively high mercury methylation and bioaccumulation. Nelson''s Sparrows (Ammodramus nelsoni) use marsh habitats year-round and have been documented to exhibit tissue mercury concentrations that exceed negative effects thresholds. We sought to further characterize the potential risk of Nelson''s Sparrows to mercury exposure by sampling individuals from sites within the range of each of its subspecies.

Methodology/Principal Findings

From 2009 to 2011, we captured adult Nelson''s Sparrows at sites within the breeding range of each subspecies (A. n. nelsoni: Grand Forks and Upham, North Dakota; A. n. alterus: Moosonee, Ontario; and A. n. subvirgatus: Grand Manan Island, New Brunswick) and sampled breast feathers, the first primary feather (P1), and blood for total mercury analysis. Mean blood mercury in nelsoni individuals captured near Grand Forks ranged from 0.84±0.37 to 1.65±1.02 SD ppm among years, between 2.0 and 4.9 times as high as concentrations at the other sites (P<0.01). Breast feather mercury did not vary among sites within a given sampling year (site means ranged from 0.98±0.69 to 2.71±2.93 ppm). Mean P1 mercury in alterus (2.96±1.84 ppm fw) was significantly lower than in any other sampled population (5.25±2.24–6.77±3.51 ppm; P≤0.03).

Conclusions/Significance

Our study further characterized mercury in Nelson''s Sparrows near Grand Forks; we documented localized and potentially harmful mercury concentrations, indicating that this area may represent a biological mercury hotspot. This finding warrants further research to determine if wildlife populations of conservation or recreational interest in this area may be experiencing negative effects due to mercury exposure. We present preliminary conclusions about the risk of each sampled population to mercury exposure.     

Photosynthetic vesicles with bound phycobilisomes from Anabaena variabilis

Photosynthetically active vesicles with attached phycobilisomes from Anabaena variabilis, were isolated and shown to transfer excitation energy from phycobiliproteins to F696 chlorophyll (Photosystem II). The best results were obtained when cells were disrupted in a sucrose/phosphate/citrate mixture (0.3 : 0.5 : 0.3 M, respectiely) containing 1.5% serum albumin. The vesicles showed a phycocyanin/chlorophyll ratio essentially identical to that of whole cells, and oxygen evolution rates of 250 μmol O₂/h per mg chlorophyll (with 4 mM ferricyanide added as oxidant), whereas whole cells had rates of up to 450. Excitation of the vesicles by 600 nm light produced fluorescence peaks (?196°C) at 644, 662, 685, 695, and 730 nm. On aging of the vesicles, or upon dilution, the fluorescence yield of the 695 nm emission peak gradually decreased with an accompanying increase and final predominant peak at 685 nm. This shift was accompanied by a decrease in the quantum efficiency of Photosystem II activity from an initial 0.05 to as low as 0.01 mol O₂/einstein (605 nm), with a lesser change in the V_max values. The decrease in the quantum efficiency is mainly attributed to excitation uncoupling between phycobilisomes and Photosystem II. It is concluded that the F685 nm emission peak, often exclusively attributed to Photosystem II chlorophyll, arises from more than one component with phycobilisome emission being a major contributor. Vesicles from which phycobilisomes had been removed, as verified by electron microscopy and spectroscopy, had an almost negligible emission at 685 nm.     

Methods for Measuring Specific Rates of Mercury Methylation and Degradation and Their Use in Determining Factors Controlling Net Rates of Mercury Methylation

A method was developed to estimate specific rates of demethylation of methyl mercury in aquatic samples by measuring the volatile ¹⁴C end products of ¹⁴CH₃HgI demethylation. This method was used in conjunction with a ²⁰³Hg²⁺ radiochemical method which determines specific rates of mercury methylation. Together, these methods enabled us to examine some factors controlling the net rate of mercury methylation. The methodologies were field tested, using lake sediment samples from a recently flooded reservoir in the Southern Indian Lake system which had developed a mercury contamination problem in fish. Ratios of the specific rates of methylation/demethylation were calculated. The highest ratios of methylation/demethylation were calculated. The highest ratios of methylation/demethylation occurred in the flooded shorelines of Southern Indian Lake. These results provide an explanation for the observed increases in the methyl mercury concentrations in fish after flooding.     

Mercury in Scalp Hair Near the Mid-Atlantic Ridge (MAR) in Relation to High Fish Consumption

The aim of this study was to evaluate the potential risk of mercury contamination near the Mid-Atlantic Ridge relating total mercury (THg) concentrations in the human scalp hair (n?=?110) and high fish consumption levels. THg was quantified in human scalp hair, and volunteers were questioned about age, gender, and smoking habits being subsequently grouped in categories based on the individual average intake of fish meals per week. THg concentrations ([THg]) in hair samples ranged from 0.05 to 2.24 μg g^?1, and significant differences were found according to age (p?<?0.05) and also among volunteers presenting different fish consumption rates (p?<?0.001) being the highest [THg] observed on the adult population and also on volunteers that indicated consuming five or more meals of fish per week. Results indicate a pattern of increased mercury accumulation with increasing fish consumption. Despite mercury availability and a potential mercury intake of up to seven times, the WHO provisional tolerable weekly intake of mercury value, in consequence of high fish consumption, mercury concentrations in scalp hair are comparatively low regarding recommended levels by WHO.     

Cytogenetic monitoring of fishermen with environmental mercury exposure

Due to high mercury levels in many Mediterranean aquatic organisms, people who live in this area and consume large amounts of seafood are exposed to a toxicological hazard. A group of 51 fishermen exposed to mercury through eating contaminated seafood from the northern Tyrrhenian Sea underwent cytogenetic monitoring. This work is part of a research project consisting of the evaluation of micronuclei (MN), chromosomal aberrations (CA) and sister-chromatid exchanges (SCE) in peripheral blood lymphocytes. Here we present data on mercury levels in blood and on micronucleus frequencies in peripheral blood lymphocytes of fishermen. The range of mercury concentrations in blood was 10.08–304.11 ng/g fresh weight, the average was 88.97±54.09 ng/g. Micronucleus frequency was defined with at least 2000 binucleated cells scored for each person; the average was 8.74 ± 2.56 expressed on 1000 binucleated cells. A statistical correlation was found between MN frequency and total mercury concentration in blood (p = 0.00041, r = 0.674), as well as between MN frequency and age (p = 0.017). No other parameters taken into account correlated with MN frequency.     

Pseudomonas putida Strains Which Constitutively Overexpress Mercury Resistance for Biodetoxification of Organomercurial Pollutants

Improved biocatalysts for mercury (Hg) remediation were generated by random mutagenesis of Pseudomonas putida with a minitransposon containing merTPAB, the structural genes specifying organomercury resistance. Subsequent selection for derivatives exhibiting elevated resistance levels to phenylmercury allowed the isolation of strains that constitutively express merTPAB at high levels, conferring the ability to cleave Hg from an organic moiety and reduce the freed Hg(II) to the less toxic elemental form, Hg⁰, at greater rates. Constitutive overexpression of merTPAB had no apparent effect on culture growth rates, even when Hg(II) was initially present at otherwise toxic concentrations. These properties were also combined with benzene and toluene catabolism, allowing detoxification of the metal component of phenyl mercuric acetate, as well as degradation of its aromatic moiety.     

A Rhizosphere-Associated Symbiont,Photobacterium spp. Strain MELD1, and Its Targeted Synergistic Activity for Phytoprotection against Mercury

Though heavy metal such as mercury is toxic to plants and microorganisms, the synergistic activity between them may offer benefit for surviving. In this study, a mercury-reducing bacterium, Photobacterium spp. strain MELD1, with an MIC of 33 mg . kg^-1 mercury was isolated from a severely mercury and dioxin contaminated rhizosphere soil of reed (Phragmites australis). While the whole genome sequencing of MELD1 confirmed the presence of a mer operon, the mercury reductase MerA gene showed 99% sequence identity to Vibrio shilloni AK1 and implicates its route resulted from the event of horizontal gene transfer. The efficiency of MELD1 to vaporize mercury (25 mg . kg^-1, 24 h) and its tolerance to toxic metals and xenobiotics such as lead, cadmium, pentachlorophenol, pentachloroethylene, 3-chlorobenzoic acid, 2,3,7,8-tetrachlorodibenzo-p-dioxin and 1,2,3,7,8,9-hexachlorodibenzo-p-dioxin is promising. Combination of a long yard bean (Vigna unguiculata ssp. Sesquipedalis) and strain MELD1 proved beneficial in the phytoprotection of mercury in vivo. The effect of mercury (Hg) on growth, distribution and tolerance was examined in root, shoot, leaves and pod of yard long bean with and without the inoculation of strain MELD1. The model plant inoculated with MELD1 had significant increases in biomass, root length, seed number, and increased mercury uptake limited to roots. Biolog plate assay were used to assess the sole-carbon source utilization pattern of the isolate and Indole-3-acetic acid (IAA) productivity was analyzed to examine if the strain could contribute to plant growth. The results of this study suggest that, as a rhizosphere-associated symbiont, the synergistic activity between the plant and MELD1 can improve the efficiency for phytoprotection, phytostabilization and phytoremediation of mercury.     

Evidence for Involvement of Gut-Associated Denitrifying Bacteria in Emission of Nitrous Oxide (N2O) by Earthworms Obtained from Garden and Forest Soils

Earthworms (Aporrectodea caliginosa, Lumbricus rubellus, and Octolasion lacteum) obtained from nitrous oxide (N₂O)-emitting garden soils emitted 0.14 to 0.87 nmol of N₂O h⁻¹ g (fresh weight)⁻¹ under in vivo conditions. L. rubellus obtained from N₂O-emitting forest soil also emitted N₂O, which confirmed previous observations (G. R. Karsten and H. L. Drake, Appl. Environ. Microbiol. 63:1878–1882, 1997). In contrast, commercially obtained Lumbricus terrestris did not emit N₂O; however, such worms emitted N₂O when they were fed (i.e., preincubated in) garden soils. A. caliginosa, L. rubellus, and O. lacteum substantially increased the rates of N₂O emission of garden soil columns and microcosms. Extrapolation of the data to in situ conditions indicated that N₂O emission by earthworms accounted for approximately 33% of the N₂O emitted by garden soils. In vivo emission of N₂O by earthworms obtained from both garden and forest soils was greatly stimulated when worms were moistened with sterile solutions of nitrate or nitrite; in contrast, ammonium did not stimulate in vivo emission of N₂O. In the presence of nitrate, acetylene increased the N₂O emission rates of earthworms; in contrast, in the presence of nitrite, acetylene had little or no effect on emission of N₂O. In vivo emission of N₂O decreased by 80% when earthworms were preincubated in soil supplemented with streptomycin and tetracycline. On a fresh weight basis, the rates of N₂O emission of dissected earthworm gut sections were substantially higher than the rates of N₂O emission of dissected worms lacking gut sections, indicating that N₂O production occurred in the gut rather than on the worm surface. In contrast to living earthworms and gut sections that produced N₂O under oxic conditions (i.e., in the presence of air), fresh casts (feces) from N₂O-emitting earthworms produced N₂O only under anoxic conditions. Collectively, these results indicate that gut-associated denitrifying bacteria are responsible for the in vivo emission of N₂O by earthworms and contribute to the N₂O that is emitted from certain terrestrial ecosystems.     

Light-dependent Emission of Hydrogen Sulfide from Plants

With the aid of a sulfur-specific flame photometric detector, an emission of volatile sulfur was detected from leaves of cucumber (Cucumis sativus L.), squash and pumpkin (Cucurbita pepo L.), cantaloupe (Cucumis melo L.), corn (Zea mays L.), soybean (Glycine max [L.] Merr.) and cotton (Gossypium hirsutum L.). The emission was studied in detail in squash and pumpkin. It occurred following treatment of the roots of plants with sulfate and was markedly higher from either detached leaves treated via the cut petiole, or whole plants treated via mechanically injured roots. Bisulfite elicited higher rates of emission than sulfate. The emission was completely light-dependent and increased with light intensity. The rate of emission rose to a maximum and then declined steadily toward zero in the course of a few hours. However, emission resumed after reinjury of roots, an increase in light intensity, an increase in sulfur anion concentration, or a dark period of several hours.

The emission was identified as H₂S by the following criteria: it had the odor of H₂S; it was not trapped by distilled H₂O, but was trapped by acidic CdCl₂ resulting in the formation of a yellow precipitate, CdS; it was also trapped by base and the contents of the trap formed methylene blue when reacted with N,N-dimethyl-p-phenylenediamine and Fe³⁺.

H₂S emission is not the cause of leaf injury by SO₂, since bisulfite produced SO₂ injury symptoms in dim light when H₂S emission was low, while sulfate did not produce injury symptoms in bright light when H₂S emission was high.

The maximum rates of emission observed, about 8 nmol min⁻¹ g fresh weight⁻¹, are about the activity that would be expected for the sulfur assimilation pathway of a normal leaf. H₂S emission may be a means by which the plant can rid itself of excess inorganic sulfur when HS⁻ acceptors are not available in sufficient quantity.

     

Transformation of Elemental Mercury by Bacteria

The fate and impact of elemental mercury in closed bacterial cultures were examined. The quantity of elemental mercury oxidized by bacteria ranged from small amounts for Pseudomonas aeruginosa, P. fluorescens, Escherichia coli, and Citrobacter to essentially all of the added elemental mercury for Bacillus subtilis and B. megaterium. The percentage of the total mercury in the system associated with bacterial cells ranged from 18.6 43.2%. Growth of the two Pseudomonas species was inhibited by elemental mercury, whereas growth of the other cultures was not distinguishable from that in mercury-free controls. No methylmercury was formed by the six cultures within 48 h.     

The preparation and properties of a stable mercury derivative of transfer RNAs from Escherichia coli

Further investigations into the properties of the mercury derivative formed by the reaction of 4-thiouridine-containing tRNAs and pentafluorophenylmercury chloride have been carried out. tRNA^fMet (which contains only one 4-thiouridine residue) has been isolated by a one-step column Chromatographic procedure from unfractionated Escherichia coli tRNA and has been shown to react with the mercury compound to give a derivative which has similar properties to those previously reported for the corresponding mercury derivative of tRNA^Tyr which contains two adjacent 4-thiouridine residues. The mercury derivative of tRNA^Tyr appears to be a competitive inhibitor of tRNA^Tyr in the aminoacylation reaction (tRNA^TyrK_m = 0.42 μM, mercury derivative of tRNA^TyrK_i = 0.11 μM). The mercury derivative of Tyr-tRNA^Tyr can be made, but only by the reaction of the mercury compound with the aminoacylated tRNA.