Microbial reduction of iron

Lovley DR. 1995. Microbial reduction of iron, manganese, and other metals. Adv Agr 54 175-231. 

Campbell, K.M., Malasarn, D., Saltikov, C.W. et al. (2006) Simultaneous microbial reduction of iron(III) and arsenic(V) in suspensions of hydrous ferric oxide. Environmental Science and Technology, 40(19), 5950-55. 

Bonneville, S., Van Cappellen, P., and Behrends, T., 2004. Microbial reduction of iron(III) oxyhy-... 

The conditions prevailing in the these column experiments may be regarded as an extreme case since reducing conditions in natural porous media often involve the presence of significant amounts of dissolved ferrous iron due to chemical and microbial reduction of iron(hydr)oxide minerals or dissolution of Fe(II)-containing minerals. Thus, in natural anoxic media, re-adsorption of Fe(II) from solution will compete with direct microbial regeneration of reactive Fe(II) surface sites. 

A relatively high degree of corrosion arises from microbial reduction of sulfates in anaerobic soils [20]. Here an anodic partial reaction is stimulated and the formation of electrically conductive iron sulfide deposits also favors the cathodic partial reaction. 

Lovley DR, EJP Phillips (1988) Novel mode of microbial energy metabolism organic carbon oxidation coupled to dissimilatory reduction of iron or manganese. Appl Environ Microbiol 54 1472-1480. 

Nealson KH, CR Myers (1992) Microbial reduction of manganese and iron new approaches to carbon cycling. Appl Environ Microbiol 58 439-443. 

Organic Carbon Oxidation Microbially Coupled to Reduction of Fe(III)(hydr)oxide. More and more evidence is accumulating that bacteria can grow anaerobically by coupling organic carbon oxidation to the dissimilatory reduction of iron(III) oxides (Nealson, 1982 Arnold et al., 1986 Lovely and Philips, 1988 Nealson and Myers, 1990). 

Lovley, D. R and E. J. P. Phillips (1988), "Novel Mode of Microbial Energy Metabolism Organic Carbon Oxidation Coupled to Dissimilatory Reduction of Iron or Manganese", Applied and Environ. Microbiology 54/6, 1472-1480. 

Lovley DR, Phillips EJP (1988) Novel mode of microbial energy metabolism organic carbon oxidation coupled to dissimilatory reduction of iron or manganese. App Environ Microbio 54 1472-1480 Lovley DR, Stolz JF, Nord Jr GL, Phillips EJP (1987) Anaerobic production of magnetite by a dissimilatoiy iron-reducing microorganism. Nature 330 252-254... 

Roden EE, Zachara JM (1996) Microbial reduction of crystalline iron(III) oxides influence of oxide surface area and potential for cell growth. Environ Sci Technol 30 1618-1628 Roden EE, Urrutia MM (2002) Influence of biogenic Fe(II) on bacterial reduction of crystalline Fe(lll) oxides. Geomicrobio J 19 209-251... 

Ullmanrf s Encyclopedia of Technical Chemistry (1992) Vol. 18,VCH, Weinheim Urmtia, M.M. Roden, E.E. Zachara, J.M. (1999) Influence of aqueous and solid-phase Fe(II) complexants on microbial reduction of crystalline iron(III) oxides. Environ. Sci. Techn. 33 4022-4028... 

For a detailed discussion of the various pathways and stoichiometries, see reference 14. However, the question remains open as to which redox process provides the electrons for reaction 6. When buried in sediments, ferric iron may be used by microorganisms as an electron acceptor (15-17). On the other hand, it also comes into contact with reductants like H2S (18, 19). Although microbial reduction of ferric oxides using sulfide as the reductant has not yet been documented (17), various studies support a purely chemical interaction between these two compounds (20-22). 

Figure 6. An idealized scheme for a sedimentary porous medium with pore walls covered by a biofilm. High sulfate reduction rates are maintained even in depths to which sulfate cannot diffuse because of recycling of sulfate within the biofilm. Numbered points (in black circles) denote the following processes I, Respiration consumes oxygen. 2, Microbial reduction of reactive metal Oxides. Reduction of reactive ferric oxides is in equilibrium with reoxidation of ferrous iron by Os. Thus, no net loss of reactive iron takes place in these layers. 3, Microbial reduction of ferric oxides. 4, Sulfate reduction rate (denoted as SRR). 5, Sulfide oxidation, either microbiologically or chemically. 6, Sulfide builds up within the hiofilm, sulfate consumption increases, reactive iron pool decreases. 7, Formation of iron sulfides.

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

Iron(II) silicates are widely distributed in nature. Most of the iron in the primary magmatic rocks is in the form of Fe(II) silicates (olivines, pyroxenes, amphiboles, andbiotites). When exposed on the Earth s surface, they undergo oxidative hydrolytic weathering to give iron(III) hydroxyoxides such as goethite, the overall stoichiometry being described by equation (1). This form of iron is very insoluble, but subsequent microbial reduction to iron(II) makes it available to the biosphere. 

Myers C. R. and Nealson K. H. (1988) Microbial reduction of manganese oxides interactions with iron and sulfur. Geochim. Cosmochim. Acta 52, 2727-2732. 

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