Chapter 8 : Microbial Mercury Reduction

MyBook is a cheap paperback edition of the original book and will be sold at uniform, low price.

Preview this chapter:
Zoom in

Microbial Mercury Reduction, Page 1 of 2

| /docserver/preview/fulltext/10.1128/9781555818098/9781555811952_Chap08-1.gif /docserver/preview/fulltext/10.1128/9781555818098/9781555811952_Chap08-2.gif


This chapter concentrates on selected aspects of microbial mercury reduction and other mechanisms of mercuric ion resistance which are relevant to the interaction of metals and microorganisms in the environment. Mercury (Hg) is simple to refine—the ores are roasted in a current of air, and metallic mercury is condensed from the vapor. The simplicity of refining and the unusual properties of this metal probably account for the long and fascinating human relationship with mercury. Hg has been released into the lithosphere, atmosphere, and hydrosphere over millennia by geochemical processes, and it is therefore an important toxic element in the biosphere. The high affinity of mercury for thiol and imino nitrogen groups in proteins and the diverse cellular targets of mercuric ions preclude some of the main strategies used by microorganisms to avoid, eliminate, or detoxify other toxic metals. Using the criterion that a specific metal resistance is regulated by a specific discriminatory, regulatory component, some of the mechanisms discussed are simply tolerance mechanisms. Experimental and pilot scale microbial mercury reduction and volatilization systems have been developed for removal of Hg(II). Hg is an underexploited model system for the study of the evolution of an environmental trait across different prokaryotic genera. Great progress has been made in one's understanding of the genetics and biochemistry of reductive Hg.

Citation: Hobman J, Wilson J, Brown N. 2000. Microbial Mercury Reduction, p 177-197. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch8

Key Concept Ranking

Mobile Genetic Elements
Highlighted Text: Show | Hide
Loading full text...

Full text loading...


Image of Figure 1
Figure 1

Microbial transformations in the mercury cycle. A schematic summary of microbial mercury transformations is shown. The levels of Hg(II) and MMHg are governed by the balance of reduction and oxidation by aerobic bacteria and by the rate of bacterial methylation and demethylation. Demethylation of MMHg can be reductive (broad-spectrum mer operons), generating CH as a metabolite, or oxidative, where CO is produced. Both Hg(II) and MMHg can pass into the food chain or be adsorbed by organic matter (particulate or dissolved). Hg(II) and MMHg will be released back into the mercury cycle when the biomass decays. Under anoxic conditions, the reaction of MMHg with HS (generated by sulfate-reducing bacteria from sulfates) produces dimethylmercuric sulfide. This is unstable and degrades to insoluble HgS and volatile DMHg. DMHg can degrade under mild acid conditions to form CH and Hg(II), which can be transformed to Hg(0). Modified from Baldi, 1997 ( ).

Citation: Hobman J, Wilson J, Brown N. 2000. Microbial Mercury Reduction, p 177-197. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch8
Permissions and Reprints Request Permissions
Download as Powerpoint
Image of Figure 2
Figure 2

Generalized model of bacterial resistance to mercury. The diagram shows the model for mercuric ion resistance in gram-negative bacteria. Mercuric ions in the environment of a bacterial cell [a] pass through the porins (OmpC and OmpF) in the outer membrane, where they are [b] scavenged by the periplasmic protein, MerP and bind to the cysteine residues in each subunit of the protein, [c] The mercuric ion is then passed from the cysteines in MerP, to those in the transmembrane region of the inner membrane protein, MerT. As part of the transport mechanism, the Hg(II) ion is transferred to the cysteines on the cytoplasmic face of MerT, whence [d] they are passed to the heavy-metal associated motif in the amino-terminal MerP-like domain of mercuric reductase [e]. The mercuric ion is then bound at the active site and reduced to elemental mercury, Hg(0) [f]. The volatile product is released from the enzyme and diffuses through the bacterial membranes to the environment. MMHg can diffuse in through the cell membrane, and with broad-spectrum determinants, is cleaved by organomercurial lyase [g]. The Hg(II) so produced is proposed to bind to glutathione in the cytoplasm and be reduced by MR. Resistance in gram-positive bacteria operates by a similar mechanism, but the detailed structures of the transport proteins are different. Cysteine residues are also present in other mercury transport proteins from gram-negative sources (e.g., MerC and MerF) or from gram-positive sources and are predicted to lie in the transmembrane region. The MR from gram-negative and gram-positive sources are similar but differ in the number (0, 1, or 2) of MerP-like N-terminal domains and in their detailed amino acid sequences.

Citation: Hobman J, Wilson J, Brown N. 2000. Microbial Mercury Reduction, p 177-197. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch8
Permissions and Reprints Request Permissions
Download as Powerpoint
Image of Figure 3
Figure 3

General organization of the Tn501 and related mer operons in gram-negative bacteria. A generalized schematic diagram of the mer genes of transposon Tn501 is shown. Additional genes from closely related mer resistances (referred to in the text), and their positions in the operon relative to merR, mer-T, mer-P, merA, and mer-D are marked. The merR and structural gene transcripts are shown as arrows from the mer operator/promoter (merO/P) site. The terminal inverted repeat (IR) of the transposon (Tn501) is marked. There are a number of other gram-negative bacterium mer operons whose organizations do not conform to this generalized structure yet whose genes are clearly closely related to Tn501 and Tn21 ( ).

Citation: Hobman J, Wilson J, Brown N. 2000. Microbial Mercury Reduction, p 177-197. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch8
Permissions and Reprints Request Permissions
Download as Powerpoint


1. Ansari, A. Z.,, J. E. Bradner,, and T. V. O'Halloran. 1995. DNA-bend modulation in a repressor-to-activator switching mechanism. Nature 374:371375.
2. Ansari, A. Z.,, M. L. Chael,, and T. V. O'Halloran. 1995. Allosteric underwinding of DNA is a critical step in positive control of transcription by Hg-MerR. Nature 355:8789.
3. Anspach, F. B.,, M. Hukel,, M. Brunke,, H. Schutte,, and W. D. Deckwer. 1994. Immobilization of mercuric reductase from a Pseudomonas putida strain on different activated carriers. Appl. Biochem. Biotechnol 44:135150.
4. Baldi, F. 1997. Microbial transformation of mercury species and their importance in the biogeochemical cycle of mercury. Metal Ions Biol Syst. 34:213257.
5. Baldi, F.,, F. Parati,, and M. Filippelli. 1995. Dimethylmercury and dimethylmercury-sulfide of microbial origin in the biogeochemical cycle of Hg. Water Air Soil Pollut. 80:805815.
6. Baldi, F.,, M. Pepi,, and M. Filippelli. 1993. Methylmercury resistance in Desulfovibrio desulfuricans strains in relation to methylmercury degradation. Appl. Environ. Microbiol. 59:24792485.
7. Barkay, T.,, D. L. Fouts,, and B. H. Olson. 1985. Preparation of a DNA gene probe for detection of mercury resistance genes in gram-negative bacterial communities. Appl. Environ. Microbiol. 49: 686692.
8. Barkay, T.,, C. Liebert,, and M. Gillman. 1989. Hybridization of DNA probes with whole-community genome for detection of genes that encode microbial responses to pollutants—mer genes and Hg2+ resistance. Appl. Environ. Microbiol. 55:15741577.
9. Barkay, T.,, R. R. Turner,, A. Van den Brook,, and C. Liebert. 1991. The relationship of Hg(II) volatilization from a fresh-water pond to the abundance of mer genes in the gene pool of the indigenous microbial community. Microb. Ecol 21:151161.
10. Begley, T. P.,, A. E. Walts,, and C. T. Walsh. 1986. Bacterial organomercurial lyase: overproduction, isolation and characterization. Biochemistry 25:71867192.
11. Bogdanova, E. S.,, I. A. Bass,, L. S. Minakhin,, M. A. Petrova,, S. Z. Mindlin,, A. A. Volodin,, E. S. Kalyaeva,, J. M. Tiedje,, J. L. Hobman,, N. L. Brown,, and V. G. Nikiforov. 1998. Horizontal spread of mer operons among Gram-positive bacteria in natural environments. Microbiology 144: 609620.
12. Bohlander, F. A.,, A. O. Summers,, and R. B. Meagher. 1981. Cloning a promoter that puts the expression of tetracycline resistance under the control of the regulatory elements of the mer operon. Gene 15:395403.
13. Boudou, A.,, and F. Ribeyre. 1997. Mercury in the food web: accumulation and transfer mechanisms. Metal Ions Biol. Syst. 34:289320.
14. Bremner, I. 1974. Heavy metal toxicities. Q. Rev. Biophys. 7:75124.
15. Brown, N. L.,, K. R. Brocklehurst,, B. Lawley,, and J. L. Hobman. 1998. Metal regulation of gene expression in bacterial systems. NATO ASI Ser.H 103:159173.
16. Brown, N. L.,, B. T. O. Lee,, and S. Silver. 1994. Bacterial transport of and resistance to copper. Metal Ions Biol. Syst. 30:405434.
17. Bruce, K. D.,, W. D. Hiorns,, J. L. Hobman,, A. M. Osborn,, P. Strike,, and D. A. Ritchie. 1992. Amplification of DNA from native populations of soil bacteria by using the polymerase chain reaction. Appl. Environ. Microbiol. 58:34133416.
18. Bruce, K. D.,, A. M. Osborn,, A. J. Pearson,, P. Strike,, and D. A. Ritchie. 1995. Genetic diversity within mer genes directly amplified from communities of noncultivated soil and sediment bacteria. Mol. Ecol. 4:605612.
19. Bull, P. C.,, and D. W. Cox. 1994. Wilson disease and Menkes disease: new handles on heavy-metal transport. Trends Genet. 10:246252.
20. Chang, J.-S.,, and J. Hong. 1994. Biosorption of mercury by the inactivated cells of Pseudomonas aeruginosa PU21 (Rip64). Biotechnol. Bioeng. 44:9991006.
21. Chang, J.-S.,, and W.-S. Law. 1998. Development of microbial mercury detoxification processes using a mercury hyperresistant strain of Pseudomonas aeruginosa PU21. Biotechnol Bioeng. 57: 462470.
22. Chen, S.,, and D. B. Wilson. 1997. Genetic engineering of bacteria and their potential for Hg2+ bioremediation. Biodegradation 8:97103.
23. Chen, S.,, and D. B. Wilson. 1997. Construction and characterization of Escherichia coli genetically engineered for bioremediation of Hg2+-contaminated environments. Appl. Environ. Microbiol. 63: 24422445.
24. Clark, D. L.,, A. A. Weiss,, and S. Silver. 1977. Mercury and organomercurial resistances determined by plasmids in Pseudomonas. J. Bacteriol. 132:186196.
25. Compeau, G. C.,, and R. Bartha. 1984. Methylation and demethylation of mercury under controlled redox, pH, and salinity conditions. Appl. Environ. Microbiol 48:12031207.
26. Compeau, G. C.,, and R. Bartha. 1985. Sulfate reducing bacteria: principal methylators of mercury in anoxic estuarine sediment. Appl. Environ. Microbiol 50:498502.
27. Compeau, G. C.,, and R. Bartha. 1987. Effect of salinity on mercury-methylating activity of sulfate-reducing bacteria in estuarine sediments. Appl. Environ. Microbiol 53:261265.
28. Condee, C. W.,, and A. O. Summers. 1992. A mer-lux transcriptional fusion for real-time examination of in vivo gene-expression kinetics and promoter response to altered superhelicity. J. Bacteriol. 174:80948101.
29. Cooksey, D. A. 1993. Copper uptake and resistance in bacteria. Mol. Microbiol. 7:15.
30. Cummings, R. T.,, and C. T. Walsh. 1992. Interaction of Tn501 mercuric reductase and dihydroflavin adenine anion with metal ions—implications for the mechanism of mercuric reductase mediated Hg(II) reduction. Biochemistry 31:10201030.
31. De Flora, S.,, C. Benicelli,, and M. Bagnasco. 1994. Genotoxicity of mercury compounds. A review. Mutat. Res. 317:5779.
32. Diels, L.,, Q. H. Dong,, D. Van der Lelie,, W. Baeyens,, and M. Mergeay. 1995. The czc operon of Alcaligenes eutrophus CH34—from resistance mechanism to the removal of heavy metals. J. Ind. Microbiol. 14:142153.
33. Earles, M. P. 1964. A case of mass mercury poisoning with mercury vapour on board H.M.S. Triumph at Cadiz, 1810. Med. Hist. 8:281286.
34. Eccles, H. 1995. Removal of heavy metals from effluent streams—why select a biological process? Int. Biodeterior. Biodegrad. 35:516.
35. Eccles, H.,, G. W. Garnham,, C. R. Lowe,, and N. C. Bruce. March 1996. Biosensors for detecting metal ions capable of being reduced by reductase enzymes. U.S. patent 5500351.
36. Fitzgerald, W. F.,, and R. P. Mason. 1997. Biogeochemical cycling of mercury in the marine environment. Metal Ions Biol. Syst. 34:53111.
37. Foster, T. J. 1987. The genetics and biochemistry of mercury resistance. Crit. Rev. Microbiol 15: 117140.
38. Fox, B.,, and C. T. Walsh. 1982. Mercuric reductase. Purification and characterization of a transposon-encoded flavoprotein containing an oxidation-reduction-active disulfide. J. Biol. Chem. 257: 24982503.
39. Fox, B. S.,, and C. T. Walsh. 1983. Mercuric reductase—homology to glutathione reductase and lipoamide dehydrogenase-iodoacetamide alkylation and sequence of the active-site peptide. Biochemistry 22:40824088.
40. Friberg, L. (ed.) 1991. Environmental Health Criteria no. 118. Inorganic Mercury. World Health Organization, Geneva, Switzerland.
41. Furukawa, K.,, T. Suzuki,, and S. Tonomura. 1969. Decomposition of organic mercurial compounds by mercury resistant bacteria. Agric. Biol. Chem. 33: 128130.
42. Gadd, G. M. 1993. Microbial formation and transformation of organometallic and organometalloid compounds. FEMS Microbiol. Rev. 11:297316.
43. Ganser, A. L.,, and D. A. Kirschner. 1985. The interaction of mercurials with myelin—comparison of in vitro and in vivo effects. Neurotoxicology 6:6377.
44. Gilbert, M. P.,, and A. O. Summers. 1988. The distribution and divergence of DNA sequences related to the Tn21 and Tn501 mer operons. Plasmid 20:127136.
45. Goldwater, L. J. 1972.Mercury: a History of Quicksilver. York Press, Baltimore, Md..
46. Gruenwendel, D. W.,, and N. Davidson. 1966. Complexing and denaturation of DNA by methyl-mercuric hydroxide. I. Spectrophotometric studies. J. Mol. Biol., 21:129144.
47. Gutknecht, J. 1981. Inorganic mercury (Hg2+) transport through lipid bilayer membranes. J. Membr. Biol 61:6166.
48. Hall, B. D.,, R. A. Bodaly,, R. J. P. Fudge,, J. W. M. Rudd,, and D. M. Rosenburg. 1997. Food as the dominant pathway of methylmercury uptake by fish. Water Air Soil Pollut. 100:324.
49. Harada, M. 1995. Minamata disease- methylmercury poisoning in Japan caused by environmental pollution. Crit. Rev. Toxicol. 25:124.
50. Hobman, J.,, G. Kholodii,, V. Nikiforov,, D. A. Ritchie,, P. Strike,, and O. Yurieva. 1994. The nucleotide sequence of the mer operon of pMER327/419 and transposon ends of pMEr327/419, 330 and 05. Gene 146:7378.
51. Hobman, J. L.,, and N. L. Brown. 1997. Bacterial mercury-resistance genes. Metal Ions Biol. Syst. 34:527568.
52. Horn, J. M.,, M. Brunke,, W. D. Deckwer,, and K. N. Timmis. 1994. Pseudomonas putida strains which constitutively overexpress mercury resistance for biodetoxification of organomercurial pollutants. Appl. Environ. Microbiol. 60:357362.
53. Huckle, J. W.,, A. P. Morby,, J. S. Turner,, and N. J. Robinson. 1993. Isolation of a prokaryotic metallothionein locus and analysis of transcriptional control by trace metal ions. Mol. Microbiol. 7: 177187.
54. Inoue, C.,, K. Sugawara,, and T. Kusano. 1990. Thiobacillus ferrooxidans mer operon: sequence analysis of the promoter and adjacent genes. Gene 96:115120.
55. Jeffrey, W. H.,, S. Nazaret,, and R. Vonhaven. 1994. Improved method for recovery of messenger RNA from aquatic samples and its application to detection of mer expression. Appl. Environ. Microbiol. 60:18141821.
56. Jeffrey, W. H.,, S. Nazaret,, and T. Barkay. 1996. Detection of the merA gene and its expression in the environment. Microb. Ecol. 32:293303.
57. Kim, K.-H.,, P. J. Hanson,, M. O. Barnett,, and S. E. Lindberg. 1997. Biogeochemistry of mercury in the air-soil-plant system. Metal Ions Biol. Syst. 34:185212.
58. Kiyono, M.,, T. Omura,, H. Fujimori,, and H. Pan-Hou. 1995. Lack of involvement of merT and merP in methylmercury transport in mercury resistant Pseudomonas K-62. FEMS Microbiol. Lett. 128:301306.
59. Klein, J.,, J. Altenbuchner,, and R. Mattes,. 1997. Genetically modified Escherichia coli for colorimetric detection of inorganic and organic Hg compounds, p. 133151. In F. W. Scheller,, F. Schubert,, and J. Fedrowitz (ed.), Frontiers in Biosensorics. 1. Fundamental Aspects. Birkhäuser Verlag, Basel, Switzerland.
60. Komura, I.,, and K. Izaki. 1971. Mechanism of mercuric chloride resistance in microorganisms. I. Vaporization of a mercury compound from mercuric chloride by multiple drug resistance strain of Escherichia coli. J. Biochem. 70:885893.
61. Krönig, B.,, and T. Paul,. 1897. Die chemischen Grundlagen der Lehre von der Giftwirkung und Desinfection, p. 163176. In T. D. Brock (ed.), Milestones in Microbiology, 1961. Prentice-Hall, Inc., Englewood Cliffs, N.J..
62. Leach, S. J. 1960. The reaction of thiol and disulphide groups with mercuric chloride and mercuric iodide. J. Aust. Chem. Soc. 13:520.
63. Lenihan, J. 1988. The Crumbs of Creation, p. 76. Adam Hilger, Bristol, United Kingdom.
64. Lindquist, O.,, Å. Jernelöv,, K. Johansson,, and H. Rohde. 1984. Mercury in the Swedish Environment: Global and Local Sources. Swedish Environmental Protection Board report no. 1816, p. 105. Swedish Environmental Protection Board, Stockholm, Sweden.
65. Lovley, D. R.,, and J. D. Coates. 1997. Bioremediation of metal contamination. Curr. Opin. Biotechnol. 8:285289.
66. Lund, P. A.,, and, N. L. Brown. 1987. Role of merT and merP gene products of transposon Tn501 in the induction and expression of resistance to mercuric ions. Gene 52:207214.
67. Magos, L. 1997. Physiology and toxicology of mercury. Metal Ions Biol. Syst. 34:321370.
68. Mason, R. P.,, J. R. Reinfelder,, and F. A. M. Morel. 1995. Bioaccumulation of mercury and methylmercury. Water Air Soil Pollut. 80:915921.
69. Meili, M. 1997. Mercury in lakes and rivers. Metal Ions Biol. Syst. 34:2152.
70. Miller, S. M.,, D. P. Ballou,, V. Massey,, C. H. Williams,, and C. T. Walsh. 1986. 2-electron reduced mercuric reductase binds Hg(II) to the active-site dithiol but does not catalyze Hg(II) reduction. J. Biol. Chem. 261:80818084.
71. Mills, A. 1990. Mercury from crematorium chimneys. Nature. 346:615.
72. Misra, T. K. 1992. Bacterial resistance to inorganic mercury salts and organomercurials. Plasmid 27:416.
73. Misra, T. K.,, N. L. Brown,, D. C. Fritzinger,, R. D. Pridmore,, W. M. Barnes,, L. Haberstroh,, and S. Silver. 1984. Mercuric ion resistance operons of plasmid R100 and transposon Tn501—the beginning of the operon including the regulatory region and the first two structural genes. Proc. Natl. Acad. Sci. USA 81:59755979.
74. Morby, A. P.,, J. L. Hobman,, and N. L. Brown. 1995. The role of cysteine residues in the transport of mercuric ions by the Tn501 MerT and MerP mercury-resistance proteins. Mol. Microbiol. 17: 11531162.
75. Mukhopadhyay, D.,, H. Yu,, G. Nucifora,, and T. K. Misra. 1991. Purification and functional characterization of MerD: a coregulator of the mercury resistance operon in Gram-negative bacteria. J. Biol. Chem. 266:1853818542.
76. Nakahara, H.,, S. Silver,, T. Miki,, and R. H. Rownd. 1979. Hypersensitivity to Hg2+ and hyper-binding activity associated with cloned fragments of the mercurial resistance operon of plasmid NR1. J. Bacteriol 140:161166.
77. Nakamura, K.,, and S. Silver. 1994. Molecular analysis of mercury-resistant Bacillus isolates from sediment of Minamata Bay, Japan. Appl Environ. Microbiol. 60:45964599.
78. Nazaret, S.,, W. H. Jeffrey,, E. Saouter,, R. Vonhaven,, and T. Barkay. 1994. merA gene expression in aquatic environments measured by messenger RNA production and Hg(II) volatilization. Appl Environ. Microbiol. 60:40594065.
79. Niebor, E.,, and D. H. S. Richardson. 1980. The replacement of the nondescript term “heavy metals” by a biologically and chemically significant classification of metal ions. Environ. Pollut. Ser. B 1:326.
80. Nies, D. H. 1995. The cobalt, zinc, and cadmium efflux system czcABC from Alcaligenes eutrophus functions as a cation-proton antiporter in Escherichia coli J. Bacteriol. 177:27072712.
81. Nies, D. H.,, and S. Silver. 1995. Ion efflux systems involved in bacterial metal resistances. J. Ind. Microbiol. 14:186199.
82. Nriagu, J. O. 1989. A global assessment of natural sources of atmospheric trace metals. Nature 338:4749.
83. Nriagu, J. O.,, and J. M. Pacyna. 1988. Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature 333:134139.
84. Nucifora, G.,, L. Chu,, S. Silver,, and T. K. Misra. 1989. Mercury operon regulation by the merR gene of the organomercurial resistance system of plasmid pDU1358. J. Bacteriol 171:42414247.
85. Nucifora, G.,, S. Silver,, and T. K. Misra. 1990. Down regulation of the mercury resistance operon by the most promoter-distal gene merD. Mol. Gen. Genet. 220:6972.
86. Ogunseitan, O. 1998. Protein method for investigating mercuric reductase gene expression in aquatic environments. Appl. Environ. Microbiol. 64:695702.
87. O'Halloran, T. V. 1993. Transition metals in control of gene-expression. Science 261:715725.
88. Olson, B. H.,, J. N. Lester,, S. M. Cayless,, and S. Ford. 1988. Distribution of mercury resistance determinants in bacterial communities of river sediments. Water Res. 23:12091217.
89. Oremland, R. S.,, C. W. Culbertson,, and M. R. Winfrey. 1991. Methylmercury decomposition in sediments and bacterial cultures: involvement of methanogens and sulfate reducers in oxidative demethylation. Appl. Environ. Microbiol. 57:130137.
90. Oremland, R. S.,, L. G. Miller,, P. Dowdle,, T. Connell,, and T. Barkay. 1995. Methylmercury oxidative degradation potentials in contaminated and pristine sediments of the Carson River, Nevada. Appl. Environ. Microbiol. 61:27452753.
91. Osborn, A. M.,, K. D. Bruce,, P. Strike,, and D. A. Ritchie. 1995. Sequence conservation between regulatory mercury resistance genes in bacteria from mercury polluted and pristine environments. Syst. Appl. Microbiol 18:16.
92. Osborn, A. M.,, K. D. Bruce,, P. Strike,, and D. A. Ritchie. 1997. Distribution, diversity and evolution of the bacterial mercury resistance (mer) operon. FEMS Microbiol. Rev. 19:239262.
93. Pak, K.-R.,, and R. Bartha. 1998. Mercury methylation by interspecies hydrogen and acetate transfer between sulfidogens and methanogens. Appl. Environ. Microbiol. 64:19871990.
94. Pan-Hou, H. S. K.,, M. Hosono,, and N. Imura. 1980. Plasmid controlled mercury biotransformation by Clostridium cochlearium T-2. Appl. Environ. Microbiol. 40:10071011.
95. Pan-Hou, H. S. K.,, M. Hosono,, and N. Imura. 1981. Role of hydrogen sulphide in mercury resistance determined by plasmid of Clostridium cochlearium T-2. Arch. Microbiol. 129:4952.
96. Pan-Hou, H. S. K.,, M. Nishimoto,, and N. Imura. 1981. Possible role of membrane proteins in mercury resistance of Enterobacter aerogenes. Arch. Microbiol. 130:9395.
97. Philippidis, G. P.,, L. H. Malmberg,, W. S. Hu,, and J. L. Schottel. 1991. Effect of gene amplification on mercuric ion reduction activity of Escherichia coli, Appl. Environ. Microbiol 57:35583564.
98. Philippidis, G. P.,, J. L. Schottel,, and W. S. Hu. 1990. Kinetics of mercuric reduction in intact and permeabilized Escherichia coli cells. Enzyme Microb. Technol. 12:854859.
99. Rasmussen, L. D.,, R. R. Turner,, and T. Barkay. 1997. Cell-density-dependent sensitivity of a mer-lux bioassay. Appl. Environ. Microbiol. 63:32913293.
100. Rensing, C.,, U. Kues,, U. Stahl,, D. H. Nies,, and B. Friedrich. 1992. Expression of bacterial mercuric ion reductase in Saccharomyces cerevisiae. J. Bacteriol. 174:12881292.
101. Rinderle, S. J.,, J. E. Booth,, and J. W. Williams. 1983. Mercuric reductase from R-plasmid NR1—characterization and mechanistic study. Biochemistry 22:869876.
102. Ritter, J. A.,, and J. P. Bibler. 1992. Removal of mercury from waste-water: large scale performance of an ion exchange process. Water Sci. Technol. 25:165172.
103. Robinson, J. B.,, and O. H. Tuovinen. 1984. Mechanisms of microbial resistance and detoxification of mercury and organomercury compounds: physiological, biochemical and genetic analysis. Microbiol. Rev. 48:95124.
104. Robinson, N. J.,, A. Gupta,, A. P. Fordham-Skelton,, R. R. D. Croy,, B. A. Whitton,, and J. W. Huckle. 1990. Prokaryotic metallothionein gene characterization and expression: chromosome crawling by ligation-mediated PCR. Proc. Ro. Soc. London B Ser. 242:241247.
105. Rochelle, P. A.,, M. K. Wetherbee,, and B. H. Olson. 1991. Distribution of DNA sequences encoding narrow-spectrum and broad-spectrum mercury resistance. Appl. Environ. Microbiol. 57: 15811589.
106. Rouch, D. A.,, B. T. O. Lee,, and A. P. Morby. 1995. Understanding cellular responses to toxic agents: a mechanism-choice in bacterial metal resistances. J. Ind. Microbiol. 14:132141.
107. Rouch, D. A.,, J. Parkhill,, and N. L. Brown. 1995. Induction of bacterial mercury-responsive and copper-responsive promoters-functional differences between inducible systems and implications for their use in gene-fusions for in-vivo metal biosensors. J. Ind. Microbiol. 14:349353.
108. Rugh, C. L.,, H. D. Wilde,, N. M. Stack,, D. M. Thompson,, A. O. Summers,, and R. B. Meagher. 1996. Mercuric ion reduction and resistance in transgenic Arabidopsis thaliana plants expressing a modified bacterial merA gene. Proc. Natl. Acad. Sci. USA 93:31823187.
109. Sahlman, L.,, W. Wong,, and J. Powlowski. 1997. A mercuric ion uptake role for the integral inner membrane protein, MerC, involved in bacterial mercuric ion resistance. J. Biol. Chem. 272:2951829526.
110. Salt, D. E.,, M. Blaylock,, N. P. B. A. Kumar,, V. Dushenkov,, B. D. Ensley,, L. Chet,, and I. Raskin. 1995. Phytoremediation: a novel strategy for the removal of toxic metals from the environment using plants. Bio/Technology 13:468474.
111. Sandstrom, A.,, and S. Lindskog. 1987. Activation of mercuric reductase by the substrate NADPH. Eur. J. Biochem. 173:411415.
112. Saouter, E.,, R. Turner,, and T. Barkay. 1994. Microbial reduction of ionic mercury for the removal of mercury from contaminated environments. Ann. N.Y. Acad. Sci. 721:423427.
113. Schiering, N.,, W. Kabsch,, M. J. Moore,, M. D. Distefano,, C. T. Walsh,, and E. F. Pai. 1991. Structure of the detoxification catalyst mercuric ion reductase from Bacillus sp. strain RC607. Nature 352:168172.
114. Schultz, P. G.,, K. G. Au,, and C. T. Walsh. 1985. Directed mutagenesis of the redox active disulfide in the flavoenzyme mercuric ion reductase. Biochemistry 24:68406848.
115. Selifonova, O.,, R. Burlage,, and T. Barkay. 1993. Bioluminescent sensors for detection of bioavailable Hg(II) in the environment. Appl. Environ. Microbiol. 59:30833090.
116. Shi, J.,, W. P. Lindsay,, J. W. Huckle,, A. P. Morby,, and N. J. Robinson. 1992. Cyanobacterial metallothionein gene expressed in Escherichia coli. Metal-binding properties of the expressed protein. FEBS Lett. 303:159163.
117. Silver, S. 1996. Bacterial metal resistance—a review. Gene 179:919.
118. Silver, S.,, G. Nucifora,, and L. T. Phung. 1993. Human Menkes X-chromosome disease and the staphylococcal cadmium-resistance ATPase—a remarkable similarity in protein sequences. Mol. Microbiol. 10:712.
119. Silver, S.,, and L. T. Phung. 1996. Bacterial heavy metal resistance: new surprises. Annu. Rev. Microbiol. 50:753789.
120. Smith, T.,, K. Pitts,, J. A. McGarvey,, and A. O. Summers. 1998. Bacterial oxidation of mercury metal vapor, Hg(0). Appl. Environ. Microbiol. 64:13281332.
121. Solioz, M.,, and C. Vulpe. 1996. CPX-type ATPases—a class of P-type ATPases that pump heavy metals. Trends Biochem. Sci. 21:237241.
122. Summers, A. O. 1986. Organisation, expression and evolution of genes for mercury resistance. Annu. Rev. Microbiol. 40:607634.
123. Summers, A. O. 1992. Untwist and shout: a heavy metal-responsive transcriptional regulator. J. Bacteriol. 174:30973101.
124. Summers, A. O.,, and T. Barkay,. 1989. Metal resistance genes in the environment, p. 287309. In S. B. Levy, and R. V. Miller (ed.), Gene Transfer in the Environment. McGraw-Hill Publishing Co., New York, N.Y..
125. Tescione, L.,, and G. Belfort. 1993. Construction and evaluation of a metal-ion biosensor. Bio-technol. Bioeng. 42:945952.
126. Trevors, J. T. 1986. Mercury methylation by bacteria. J. Basic Microbiol. 26:499504.
127. Tsai, Y.-L.,, M. J. Park,, and Â. H. Olson. 1991. Rapid method for direct extraction of mRNA from seeded soils. Appl. Environ. Microbiol. 57:765768.
128. Uno, Y.,, M. Kiyono,, T. Tezuka,, and H. Pan-Hou. 1997. Phenylmercury transport mediated by merT-merP genes of Pseudomonas K-62 plasmid pMR26. Biol. Pharm. Bull. 20:107109.
129. Virta, M.,, J. Lampinen,, and M. Karp. 1995. A luminescence-based mercury biosensor. Anal. Chem. 67:667669.
130. Volesky, B.,, and Z. R. Holan. 1995. Biosorption of heavy metals. Biotechnol. Prog. 11:235250.
131. Volotovsky, V.,, Y. J. Nam,, and N. Kim. 1997. Urease-based biosensor for mercuric ion determination. Sensors Actuators Ser. B. 42:233237.
132. Watanabe, C.,, and H. Sato. 1996. Evolution of our understanding of methylmercury as a health threat. Environ. Health Perspect. 104(Suppl. 2):367379.
133. Weast, R. C. (ed.). 1984. CRC Handbook of Chemistry and Physics, 65th ed., p. B24. CRC Press, Inc., Boca Raton, Fla..
134. Weiss, A. A.,, J. L. Schottel,, D. L., Clark,, R. G. Beller,, and S. Silver,. 1978. Mercury and organomercurial resistance with enteric, staphylococcal and pseudomonad plasmids, p. 121124. In D. Schlessiger (ed.), Microbiology-1978. American Society for Microbiology, Washington, D.C..
135. Williams, J. W.,, and S. Silver. 1984. Bacterial resistance and detoxification of heavy-metals. Enzyme Microb. Technol. 6:530537.
136. Windholz, M. (ed.). 1983. The Merck Index, 10th ed. Merck & Co., Rahway, N.J..
137. Xu, C., T. Q. Zhou,, M. Kuroda,, and B. P. Rosen. 1998. Metalloid resistance mechanisms in prokaryotes. J. Biochem. 123:1623.

This is a required field
Please enter a valid email address
Please check the format of the address you have entered.
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error