Metal-reducing bacteria

Metal-reducing bacteria, such as those that convert ferric to ferrous ion, have been suggested as an accelerant for steel corrosion in oxygenated waters, lb date, evidence of these bacteria influencing corrosion in industrial systems is scarce. 

Zachara JM, Kukkadapu RK, Fredrickson JK, Gorby YA, Smith SC (2002) Biomineralization of poorly crystalline Fe(III) oxides by dissimilatory metal reducing bacteria (DMRB). Geomicrobio J 19 179-206 Zhu XK, O Nions RK, Guo YL, Reynolds BC (2000) Secular variation of iron isotopes in North Atlantic deep water. Science 287 2000-2002... 

The process can be used to immobilize heavy metals such as Cd, Zn, Cu, Pb, Ni and Co. Cr(VI) can be reduced by some metal-reducing bacteria to the less toxic and less soluble form Cr(III). Arsenate [As(V)] can be reduced to the more mobile arsenite [As(III)] which precipitates as AS2S3, and is insoluble at low pH. Several laboratory-scale tests (batch and column) are currently available to study the feasibility of this process. However, only a few field tests have been performed to date. Two such tests have been conducted in Belgium, one at a non-ferrous industrial site, where the groundwater was contaminated with Cd, Zn, Ni and Co, and the other which was treated by injection of molasses in order to reduce chromium (VI) to chromium (III). A third demonstration in The Netherlands has been performed at a metal surface treatment site contaminated by Zn. The outcomes of a batch test of a groundwater heavily contaminated by Zn, Cd, Co and Ni are presented in Table 5. The initial sulphate concentration was 506mg/l. With the addition of acetate, a nearly... 

Islam, F.S., Gault, A.G., Boothman, C. et al. (2004) Role of metal-reducing bacteria in arsenic release from Bengal Delta sediments. Nature, 430(6995), 68-71. 

Because Mn(IV) reduction generally makes a small contribution to carbon metabolism, it is not considered in detail in this review. However, there are many similarities between the cycles of the two metals that we allude to in the text. In fact, many Fe(III)-reducing bacteria are more aptly described as metal-reducing bacteria because they also reduce Mn(IV) and a variety of other metals. A recent and excellent review of both Fe(III) and Mn(IV) cycling was provided by Thamdmp (2000), and Tebo et al. (1997) reviewed microbial Mn(IV) oxidation. 

Organic compounds have the potential to abiotically reduce Fe(III) and Mn(IV) (Luther et al., 1992 Stone, 1987). Phenols and a variety of other aromatic compounds reduce Fe(III) rapidly at acidic pH, but slowly at circum neutral pH (LaKind and Stone, 1989). Humics can reduce Fe(III) effectively at circumneutral pH and they are abundant in soils and sediments. Because humics and other organic compounds often serve as electron shuttles between metal-reducing bacteria and metal oxides (Lovley et al., 1996a), it may be difficult to separate microbial and nonmicrobial sources of electrons. Finally, aerobic photoreduction of Fe(III) has been observed in freshwater and marine environments (Barbeau et al., 2001 Emmenegger et al., 2001), but it is unknown to what degree this process... 

Organic matter is oxidized in the suboxic zone through iron or manganese reduction. This may be a direct oxidation by metal reducing bacteria or an indirect oxidation via sulfate reduction and sulfide oxidation. Does it matter for the end products which pathway dominates ... 

These experiments pointed out that respiratory reduction of As(V) sorbed to solid phases can indeed occur in nature, but its extent and the degree of mobilization of the As(III) product is constrained by the type of minerals present in a given system. What remains unclear is whether micro-organisms can actually reduce As(V) while it is attached to the mineral surface, or if they attack a mono-layer of aqueous As(V) that is in equilibrium with the As(V) adsorbed onto the surface layer. If, as is the case for dissimilatory metal-reducing bacteria such as Geobacter sulfurreducens and Shewanella oneidensis (44,45), components of the electron transport chain are localized to the outer-membrane of some arsenate-respiring bacteria, direct reductive dissolution of insoluble arsenate minerals may be possible by attached bacteria. Too little is known at present about the topology... 

B.J. Little, P. Wagner, K. Hart, R. Ray, D. Lavoie, K. Nealson, C. Aguilar. The role of metal reducing bacteria in microbiologically influenced corrosion. Paper No. 215, Corrosion 1997, NACE, Houston, TX, 1997. 

Gorby, Y.A. and Beveridge, T.J. (2005) Composition, reactivity, and regulation of extracellular metal-reducing structures (nanowires) produced by dissimilatory metal reducing bacteria, Warrenton, VA. 

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