Mercury-resistant Strain Research Articles

Isolation and Identification of Mercury-Tolerant Bacteria LBA119 from Molybdenum-Lead Mining Soils and Their Removal of Hg2.

To screen heavy metal-tolerant strains from heavy metal-contaminated soil in mining areas and determine the tolerance of the strains to different heavy metals and their removal rates through experiments. Mercury-resistant strain LBA119 was isolated from mercury-contaminated soil samples in Luanchuan County, Henan Province, China. The strain was identified by Gram staining, physiological and biochemical tests, and 16S rDNA sequences. The LBA119 strain showed good resistance and removal rates to heavy metals such as Pb2+, Hg2+, Mn2+, Zn2+, and Cd2+ using tolerance tests under optimal growth conditions. The mercury-resistant strain LBA119 was applied to mercury-contaminated soil to determine the ability of the strain to remove mercury from the soil compared to mercury-contaminated soil without bacterial biomass. Mercury-resistant strain LBA119 is a Gram-positive bacterium that appears as a short rod under scanning electron microscopy, with a single bacterium measuring approximately 0.8 × 1.3 μm. The strain was identified as a Bacillus by Gram staining, physiological and biochemical tests, and 16S rDNA sequence analysis. The strain was highly resistant to mercury, with a minimum inhibitory concentration (MIC) of 32 mg/L for mercury. Under a 10 mg/L mercury environment, the optimal inoculation amount, pH, temperature, and salt concentration of the LBA119 strain were 2%, 7, 30 °C, and 20 g/L, respectively. In the 10 mg/L Hg2+ LB medium, the total removal rate, volatilization rate, and adsorption rate at 36 h were 97.32%, 89.08%, and 8.24%, respectively. According to tolerance tests, the strain showed good resistance to Pb2+, Mn2+, Zn2+, Cd2+, and other heavy metals. When the initial mercury concentration was 50 mg/L and 100 mg/L, compared with the mercury-contaminated soil that contained an LB medium without bacterial biomass, LBA119 inoculation increased 15.54-37.67% after 30 days of culture. This strain shows high bioremediation potential for mercury-contaminated soil.

Characterization of microbial communities of soils from gold mine tailings and identification of mercury-resistant strain

To enrich the understanding of the complex environmental system of soil and microorganisms in gold tailings, we studied the effects of environmental factors on the microbial community diversity in gold mine tailing soil in Beijing, and the strains screened from the soil with serious mercury (Hg) pollution. The results showed that microbial diversity and community composition varied among sites, and at varying depths, soil microbes were significantly affected by soil environmental factors such as lead (Pb), Hg, pH, and total organic carbon (TOC). Pb and Hg negatively affected soil microbial diversity, and less-polluted soil showed increased microbial diversities and complex community structure. Community composition analysis showed that Firmicutes, Proteobacteria and Actinobacteria were the dominant microorganisms. Moreover, Hg-resistant bacterial species isolated from soil samples were identified as Pseudomonas plecoglossicida with a high Hg tolerance efficiency. This study is important in understanding the microbial diversity and function in gold mine tailing soils and can widen the application for bioremediation process.

A broad mercury resistant strain of Pseudomonas putida secretes pyoverdine under limited iron conditions and high mercury concentrations.

The Pseudomonas putida FB1, known as a broad-spectrum mercury resistant strain, becomes yellow-green due to the secretion of pyoverdine (PVDs) under limited iron conditions and high mercury concentrations. Different modified Nelson's media were obtained by adding mercury, iron, and the complexing agent nitrilotriacetic acid to demonstrate that the strain produces only the highest concentrations of PVDs due to the induction with 25µM Hg2+. An amount of 250mg PVDs was purified from the supernatant of 1litre culture. The various forms of PVDs were characterized using different techniques such as fluorescence spectroscopy, high performance liquid chromatography coupled with high resolution mass spectrometry, and scanning electron microscope equipped with energy dispersive X-ray analyser. A set of "in vivo" experiments demonstrated that additions of Hg2+ to the cultures from 10 to 25µM Hg2+ stimulate an over secretion of PVDs suggesting that the toxic cation strongly reduces the availability of apo-PVDs, because the complex mercuric-pyoverdine is very stable at neutral pH, and hinder the formation of PVDs-Fe(III).

Mercury remediation potential of a mercury resistant strain Sphingopyxis sp. SE2 isolated from contaminated soil

A mercury resistant bacterial strain SE2 was isolated from contaminated soil. The 16s rRNA gene sequencing confirms the strain as Sphingopyxis belongs to the Sphingomonadaceae family of the α-Proteobacteria group. The isolate showed high resistance to mercury with estimated concentrations of Hg that caused 50% reduction in growth (EC50) of 5.97 and 6.22mg/L and minimum inhibitory concentrations (MICs) of 32.19 and 34.95mg/L in minimal and rich media, respectively. The qualitative detection of volatilized mercury and the presence of mercuric reductase enzyme proved that the strain SE2 can potentially remediate mercury. ICP-QQQ-MS analysis of the remaining mercury in experimental broths indicated that a maximum of 44% mercury was volatilized within 6hr by live SE2 culture. Furthermore a small quantity (23%) of mercury was accumulated in live cell pellets. While no volatilization was caused by dead cells, sorption of mercury was confirmed. The mercuric reductase gene merA was amplified and sequenced. Homology was observed among the amino acid sequences of mercuric reductase enzyme of different organisms from α-Proteobacteria and ascomycota groups.

Simultaneous bioremediation and biodetection of mercury ion through surface display of carboxylesterase E2 from Pseudomonas aeruginosa PA1

Mercury is a toxic heavy metal and presents significant threats to organisms and natural ecosystems. Recently, the mercury remediation as well as its detection by environmental-friendly biotechnology has received increasing attention. In this study, carboxylesterase E2 from mercury-resistant strain Pseudomonas aeruginosa PA1 has been successfully displayed on the outer membrane of Escherichia coli Top10 bacteria to simultaneously adsorb and detect mercury ion (Hg2+). The transmission electron microscopy analysis shows that Hg2+ can be absorbed by carboxylesterase E2 and accumulated on the outer membrane of surface-displayed E. coli bacteria. The adsorption of Hg2+ followed a physicochemical, equilibrated and saturatable mechanism, which well fits the traditional Langmuir adsorption model. The surface-displayed system can be regenerated through regulating pH values. As its activity can be inhibited by Hg2+, carboxylesterase E2 has been used to detect the concentration of Hg2+ in water samples. The developed surface display system will be of great potential in the simultaneous bioremediation and biodetection of environmental mercury pollution.

Toward Bioremediation of Methylmercury Using Silica Encapsulated Escherichia coli Harboring the mer Operon.

Mercury is a highly toxic heavy metal and the ability of the neurotoxin methylmercury to biomagnify in the food chain is a serious concern for both public and environmental health globally. Because thousands of tons of mercury are released into the environment each year, remediation strategies are urgently needed and prompted this study. To facilitate remediation of both organic and inorganic forms of mercury, Escherichia coli was engineered to harbor a subset of genes (merRTPAB) from the mercury resistance operon. Protein products of the mer operon enable transport of mercury into the cell, cleavage of organic C-Hg bonds, and subsequent reduction of ionic mercury to the less toxic elemental form, Hg(0). E. coli containing merRTPAB was then encapsulated in silica beads resulting in a biological-based filtration material. Performing encapsulation in aerated mineral oil yielded silica beads that were smooth, spherical, and similar in diameter. Following encapsulation, E. coli containing merRTPAB retained the ability to degrade methylmercury and performed similarly to non-encapsulated cells. Due to the versatility of both the engineered mercury resistant strain and silica bead technology, this study provides a strong foundation for use of the resulting biological-based filtration material for methylmercury remediation.

A Bioremediation Approach to Mercury Removal in a Shake Flask Culture Using Pseudomonas putida (ATCC 49128)

Mercury is one of the most poisonous elements found on earth bonded to sulfhydryl groups of enzymes and proteins, thereby inactivating vital cell functions. Indeed this has drawn the attention of many environmental researchers who have been attempting through various mean to expunging mercury from these contaminated medium. Biological approach provided a satisfactory outcome in the clean-up of mercury contaminated soil and water due to its high potential for greater performance, environment friendliness and cost effectiveness. Mercuryresistant bacterial strain (P. putida ATCC 49128), was experimented on its potential to grow and reduce mercury to a permissible level under optimum conditions of nutrient, pH and other related physical factors in an incubator shake flask. It was observed that P. putida displayed a usual growth pattern when tried at low level mercury concentration of 1.0 μM, 6.0 μM and 19.0 μM, by exponentially growing during the first 4 hours of inoculation, but drastically decreased by the end of 24 hours’ time. This was indicated by the mercury removal rate of 99.0%, 99.83% and 98.58% in the three mercury concentrations used. Also, under the same optimum condition of growth, mercury concentration of 1000 μM was reduced by 92.0% after the first initial 1 hour to 98.0% at the end of 28 hour study. Comparably, similar trend was also observed when P. putida was used as bioaugmented organism to treat mercury contaminated samples from two petroleum industry based wastewater. A reduction rate of 84% was observed at the initial first 4 hours to about 90.5% after 96 hour experiment for plant P1 wastewater. While results from wastewater plant P2 indicated reduction rate of 97.2%, followed by 94.09% and lastly 56.8% respectively. The result affirmed the ability of this strain to optimally utilize the optimal conditional factors to grow and reduce mercury concentration overwhelmingly within a shortest time of less than 30 hours.

Mercury Resistant Bacterial Population and Characterization of Bacillus sp., Isolated From Sediment of Solid Waste Discharged Point of Steel Industry

Most of the soil bacteria which are continuously exposed to mercury present in soil and sediments of lakes and rivers have genetically adapted to resist its toxicity. In the present study, mercury resistant bacterial population was enumerated from sediment samples of Rourkela Steel Plant, Odisha and a highly mercury resistant strain (MIC = 100 ppm), identified as Bacillus sp., was characterized by various biochemical tests. Mercury levels in the collected sediments were in the range of 0.054–0.079 ppm. Percentages of mercury resistant bacteria in sediments at four sites were 42, 26.32, 67.56, 83.93 % respectively. The highly resistant strain Bacillus sp. could grow well with 7 and 8 pH, 45 °C temperature and 6 ppt NaCl concentration. MIC of Zn, Cu, Fe and Cd are 40, 40, 40 and 20 ppm respectively. The isolate Bacillus sp. SD-43 which has shown greater tolerance of mercury besides volatilizing 60.06 % of mercury as HgCl2 is attributed to the adaptation towards various stress conditions and may be potentially utilized in the process of bioremediation of mercury in contaminated area.

Isolation and identification of a mercury resistant strain

A mercury resistant strain 2 was isolated. It was identified as Pseudomonas putida and designated as Pseudomonas putida 2 on the basis of morphological and biochemical analysis in combination with phylogenetic analysis. Strain 2 could tolerate and aerobically grow in the medium containing up to of 50 mg·dm Hg(II). The highest Hg(II) removal of strain 2 was 85.2% at an initial concentration of 15 mg·dm Hg(II). The highest Hg(II) removal of strain 2 was obseved at 30 °C and pH 7.

Characterization of the Metabolically Modified Heavy Metal-Resistant Cupriavidus metallidurans Strain MSR33 Generated for Mercury Bioremediation

BackgroundMercury-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.Methodology/Principal FindingsTo improve inorganic and organic mercury resistance of strain CH34, the IncP-1β plasmid pTP6 that provides novel merB, merG genes and additional other mer genes was introduced into the bacterium by biparental mating. The transconjugant Cupriavidus metallidurans strain MSR33 was genetically and biochemically characterized. Strain MSR33 maintained stably the plasmid pTP6 over 70 generations under non-selective conditions. The organomercurial lyase protein MerB and the mercuric reductase MerA of strain MSR33 were synthesized in presence of Hg2+. The minimum inhibitory concentrations (mM) for strain MSR33 were: Hg2+, 0.12 and CH3Hg+, 0.08. The addition of Hg2+ (0.04 mM) at exponential phase had not an effect on the growth rate of strain MSR33. In contrast, after Hg2+ addition at exponential phase the parental strain CH34 showed an immediate cessation of cell growth. During exposure to Hg2+ no effects in the morphology of MSR33 cells were observed, whereas CH34 cells exposed to Hg2+ showed a fuzzy outer membrane. Bioremediation with strain MSR33 of two mercury-contaminated aqueous solutions was evaluated. Hg2+ (0.10 and 0.15 mM) was completely volatilized by strain MSR33 from the polluted waters in presence of thioglycolate (5 mM) after 2 h.Conclusions/SignificanceA broad-spectrum mercury-resistant strain MSR33 was generated by incorporation of plasmid pTP6 that was directly isolated from the environment into C. metallidurans CH34. Strain MSR33 is capable to remove mercury from polluted waters. 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.

Mercury bioaccumulation and simultaneous nanoparticle synthesis by Enterobacter sp. cells

A mercury resistant strain of Enterobacter sp. is reported. The strain exhibited a novel property of mercury bioaccumulation with simultaneous synthesis of mercury nanoparticles. The culture conditions viz. pH 8.0 and lower concentration of mercury promotes synthesis of uniform sized 2–5nm, spherical and monodispersed intracellular mercury nanoparticles. The remediated mercury trapped in the form of nanoparticles is unable to vaporize back into the environment thus, overcoming the major drawback of mercury remediation process. The mercury nanoparticles were recoverable. The nanoparticles have been characterized by high resolution transmission electron microscopy, energy dispersive X-ray analysis, powder X-ray diffraction and atomic force microscopy. The strain can be exploited for metal bioaccumulation from environmental effluent and developing a green process for nanoparticles biosynthesis.

Isolation, characterization and extraction of mer gene of Hg 2+ resisting strain D 2

Mercury-resistant strain D 2 was isolated from mercury-contaminated soil and investigations on its 16S rDNA sequence, growth, minimal inhibitory concentrations (MICs) of metals, antibiotic susceptibility and mer gene were conducted. The strain D 2 can grow in the medium containing 60 mg/L mercury ion. It presents more than 99% identity of 16S rRNA gene with Pseudomonas aeruginosa, and exhibits high MIC values for heavy metals and a large spectrum antibiotics resistance. The mer RT gene sequence was amplified from chromosome. Strain D 2 is identified as Pseudomonas aeruginosa and the resistance to mercuric ion is related to chromosome.

Volatilization of mercury by an iron oxidation enzyme system in a highly mercury-resistant Acidithiobacillus ferrooxidans strain MON-1.

A highly mercury-resistant strain Acidithiobacillus ferrooxidans MON-1, was isolated from a culture of a moderately mercury-resistant strain, A. ferrooxidans SUG 2-2 (previously described as Thiobacillus ferrooxidans SUG 2-2), by successive cultivation and isolation of the latter strain in a Fe2+ medium with increased amounts of Hg2+ from 6 microM to 20 microM. The original stain SUG 2-2 grew in a Fe2+ medium containing 6 microM Hg2+ with a lag time of 22 days, but could not grow in a Fe2+ medium containing 10 microM Hg2+. In contrast, strain MON-1 could grow in a Fe2+ medium containing 20 microM Hg2+ with a lag time of 2 days and the ability of strain MON-1 to grow rapidly in a Fe2+ medium containing 20 microM Hg2+ was maintained stably after the strain was cultured many times in a Fe2+ medium without Hg2+. A similar level of NADPH-dependent mercury reductase activity was observed in cell extracts from strains SUG 2-2 and MON-1. By contrast, the amounts of mercury volatilized for 3 h from the reaction mixture containing 7 microM Hg2+ using a Fe(2+)-dependent mercury volatilization enzyme system were 5.6 nmol for SUG 2-2 and 67.5 nmol for MON-1, respectively, indicating that a marked increase of Fe(2+)-dependent mercury volatilization activity conferred on strain MON-1 the ability to grow rapidly in a Fe2+ medium containing 20 microM Hg2+. Iron oxidizing activities, 2,3,5,6-tetramethyl-p-phenylenediamine (TMPD) oxidizing activities and cytochrome c oxidase activities of strains SUG 2-2 and MON-1 were 26.3 and 41.9 microl O2 uptake/mg/min, 15.6 and 25.0 microl O2 uptake/mg/min, and 2.1 and 6.1 mU/mg, respectively. These results indicate that among components of the iron oxidation enzyme system, especially cytochrome c oxidase activity, increased by the acquisition of further mercury resistance in strain MON-1. Mercury volatilized by the Fe(2+)-dependent mercury volatilization enzyme system of strain MON-1 was strongly inhibited by 1.0 mM sodium cyanide, but was not by 50 nM rotenone, 5 microM 2-n-heptyl-4-hydroxy-quinoline-N-oxide (HQNO), 0.5 microM antimycin A, or 0.5 microM myxothiazol, indicating that cytochrome c oxidase plays a crucial role in mercury volatilization of strain MON-1 in the presence of Fe2+.

Cytochrome c Oxidase Purified from a Mercury-Resistant Strain of Acidithiobacillus ferrooxidans Volatilizes Mercury.

We suggested in our previous study that the plasma membrane cytochrome c oxidase of the mercury-resistant iron-oxidizing bacterial strain Acidithiobacillus ferrooxidans, SUG 202, is involved in Fe2+-dependent mercury volatilization. To study the involvement of A. ferrooxidans cytochrome c oxidase in mercury reduction, the cytochrome c oxidase was extracted from mercury-resistant and mercury-sensitive strains and purified. The Fe2+-dependent mercury volatilization activities of the oxidases from these strains were compared. The cytochrome c oxidase from strain SUG 2-2 volatilized 39% of the total Hg2+ (7 nmol) that had been added to a 10-ml reaction mixture (pH 3.8) in the presence of 10 micromol of Fe2+ after a 7-d incubation period at 30 degrees C. In contrast, the enzyme purified from the mercury-sensitive strain AP19-3 volatilized 3.5% of the total mercury under the same conditions. The boiled SUG 2-2 oxidase did not exhibit activity to volatilize mercury. Fe2+ reduced the oxidase from SUG 2-2 and Hg2+ oxidized the reduced enzyme. The purified SUG 2-2 oxidase is composed of three protein subunits with apparent molecular weights of 56,000 Da (alpha), 24,000 Da (beta), and 19,000 Da (gamma). The amount of mercury bound to the purified SUG 2-2 oxidase was 6.2 microg/mg protein and those bound to alpha-, beta- and gamma-subunits of the cytochrome c oxidase were 3.5, 2.6 and 0.7 microg/mg protein, respectively.

Volatilization of mercury under acidic conditions from mercury-polluted soil by a mercury-resistant Acidithiobacillus ferrooxidans SUG 2-2.

Volatilization of mercury under acidic conditions from soil polluted with mercuric chloride (1.5 mg Hg/kg soil) was studied with resting cells of a mercury-resistant strain, Acidithiobacillus ferrooxidans SUG 2-2. When resting cells of SUG 2-2 (0.01 mg of protein) were incubated for 10 d at 30 degrees C in 20 ml of 1.6 mM sulfuric acid (pH 2.5) with ferrous sulfate (3%) and mercury-polluted soil (1 g), which contained 7.5 nmol of Hg, approximately 4.1 nmol of mercury was volatilized, indicating that 54% of the total mercury in the soil was volatilized. The amount of mercury volatilized from the soil was dependent on the concentration of Fe2+ added to the medium. When elemental sulfur, sodium tetrathionate, and pyrite were used as an electron donor for the mercury reduction, 16, 2.4 and 0.84%, respectively, of the total mercury added to the solution were volatilized. The optimum pH and temperature for mercury volatilization were 2.5 and 30 degrees C. Approximately 92% of the total mercury in a salt solution (pH 2.5) with resting cells of SUG 2-2 (0.01 mg of protein), ferrous sulfate (3%) and mercury-polluted soil (1 g) was volatilized by further addition of both resting cells and Fe2+ and by incubating for 30 d at 30 degrees C.

Characterization and theoretical analysis on toxicological threshold of mercuric ions to Pseudomonas aeruginosa PU21 (Rip64)

This study provides a novel attempt to put forward, in general terms and explanations, the toxicological threshold for Hg(II) detoxification. Quantitative analysis of mercuric ion toxicity to a mercury-resistant strain Pseudomonas aeruginosa PU21 and identification of the threshold phenomena are included. It is revealed that rate of cellular viability loss depends upon the ratio of Hg2+ concentration to cell population, (or “multiplicity of toxicity”– MOT). The threshold of unacclimated cells (or “non-growth cells” PU21u) and hyperresistant strain (PU21r) occurs at MOT of 1.6×1010∼3.2×1010 and 1.7×1011∼3.4×1011 molecules Hg2+/cfu, respectively. The threshold of PU21r increase approx. 10-fold compared with unacclimated resistant strain PU21u. This indicated that sequential treatment of culture with selection pressures (i.e. mercury-containing media) led to over 10-fold increase in mercury resistance. Thus, this quantitative evaluation of toxicity threshold among resistant populations can be used as a design criterion for long-term Hg2+ detoxification bioprocesses.

Repeated fed-batch operations for microbial detoxification of mercury using wild-type and recombinant mercury-resistant bacteria

A wild-type mercury-resistant strain Pseudomonas aeruginosa PU21 (Rip64), and an Escherichia coli PWS1 strain genetically engineered to harbor mercury resistance were examined for their capacity to detoxify soluble mercuric ions with repeated fed-batch operations. The specific mercury detoxification activity for the two strains at different initial mercury concentrations was determined by resting-cell experiments. The fed-batch operations were conducted with different initial culture volumes ( V o), inoculum sizes ( X o), and different mercury feeding rates ( F Hg) to investigate the effects of those operation parameters on the performance of mercury detoxification. The results showed that the wild-type and the recombinant strains had an optimal specific activity of 5×10 −7 and 8×10 −8 μg cell −1 h −1, respectively. In fed-batch operation for P. aeruginosa PU21, under the conditions of V o=400 ml and X o=4.5–4.8×10 9 cells ml −1 the overall mercury detoxification efficiency ( η) for F Hg=16.9 mg Hg h −1 was 5.26 mg Hg l −1 h −1, nearly 35% higher than that for a lower F Hg (11.7 mg Hg h −1). Among the three initial culture volumes examined in this study, the highest η (5.60 mg Hg l −1 h −1) was obtained when V o=1200 ml and F Hg=16.9 mg Hg h −1. It was also found that an inoculum size higher than 4.0×10 9 cells ml −1 enabled a stable fed-batch operation, while as the inoculum was reduced to around 1.6×10 9 cells ml −1, the mercury feeding caused severe cell death, leading to an unsuccessful fed-batch operation. In the fed-batch operation for E. coli PWS1 strain with V o=1200 ml and F Hg=16.9 mg Hg h −1, the mercury detoxification efficiency was 3.07 mg Hg l −1 h −1, only 54% of that for the wild-type P. aeruginosa PU21 strain under the same operating conditions. It was also noticed that the operation with E. coli PWS1 became less efficient at the second fed-batch cycle due to plasmid instability of the recombinant strain.

Volatilization of mercury from natural water by a broad-spectrum Hg-resistantBacillus pasteurii strain DR2

A broad-spectrum mercury-resistant bacterial strain was isolated from contaminated water and was identified as Bacillus pasteurii strain DR2. It could volatilize Hg-compounds including organomercurials from its growth media. It utilized several aromatic compounds as a sole source of carbon. The bacterial strain eliminated HgCl2 from sterile river water and the presence of benzene, toluene, naphthalene and nitrobenzene at 1 mM concentration in the system increased the rate of mercury volatilization, the volatilization rate being highest with benzene. When 1.7×107 cells of this bacterial strain were added per ml of non-sterile water the bacterial strain volatilized more than 90 percent of mercury from mercuric chloride and organo-mercurials like PMA, thiomersol and methoxy ethyl mercuric chloride (MEMC). In the absence of this bacterial strain the volatilization of PMA and MEMC due to the presence of other Hg-resistant organisms in nonsterile polluted water ranged between 20–25 percent and of HgCl2 was about 40 percent. However, in the presence of B. pasteurii DR2 volatilization of these Hg-compounds from non-sterile water increased by 20–40 percent. In the presence of 1 mM benzene the rate of mercury volatilization was even higher. In all the cases the rate of volatilization was higher in the first seven days than in the next seven days.

Biosorption of mercury by the inactivated cells of pseudomonas aeruginosa PU21 (Rip64)

Biomass of a mercury-resistant strain Pseudomonas aeruginosa PU21 (Rip64) and hydrogen-form cation exchange resin (AG 50W-X8) were investigated for their ability to adsorb mercury. The maximum adsorption capacity was approximately 180 mg Hg/g dry cell in deionized water and 400 mg Hg/g dry cell in sodium phosphate solution at pH 7.4, higher than the maximum mercury uptake capacity in the cation exchange resin (100 mg Hg/g dry resin in deionized water). The mercury selectivity of the biomass over sodium ions was evaluated when 50 mM and 150 mM of Na(+) were present. Biosorption of mercury was also examined in sodium phosphate solution andphosphate-buffered saline solution (pH 7.0), containing 50mM and 150 mM of Na(+), respectively. It was found that the presence of Na(+) did not severely affect the biosorption of Hg(2+), indicating a high mercury selectivity ofthe biomass over sodium ions. In contrast, the mercury uptake by the ion exchange resin was strongly inhibited by high sodium concentrations. The mercury biosorption was most favorable in sodium phosphate solution (pH 7.4), with a more than twofold increase in the maximum mercury uptake capacity. The pH was found to affect the adsorption of Hg(2+)bythe biomass and the optimal pH value was approximately 7.4. The adsorption of mercury on the biomass and the ion exchange resin appeared to follow theLangmuir or Freundlich adsorption isotherms. (c) 1994 John Wiley & Sons, Inc.

Effects of Cinnabar on Pyrite Oxidation by Thiobacillus ferrooxidans and Cinnabar Mobilization by a Mercury-Resistant Strain

The effect of cinnabar on pyrite oxidation by mercury-sensitive and mercury-resistant strains of Thiobacillus ferrooxidans was investigated by using percolation columns. Mercury-resistant strains oxidized pyrite in pyrite-cinnabar mixtures (1 and 10%, wt/wt), whereas a mercury-sensitive strain did not. Elemental mercury was produced by the mercury-resistant strains growing in the pyrite-cinnabar mixtures in percolation columns and in flasks containing cinnabar only. Manometric experiments showed that cinnabar had little effect on oxygen uptake of mercury-sensitive or mercury-resistant cells growing on ferrous sulfate, pyrite, or pyrite-ferrous sulfate mixtures. In addition, shake flask leaching experiments showed that cinnabar had little effect on pyrite oxidation at 1% (wt/wt) but inhibited growth of mercury-sensitive and mercury-resistant strains at 10%. Mercury-resistant strains were unable to grow on cinnabar as an energy source.