Dissimilatory Fe(III) and Mn(IV) Reduction
Section snippets
INTRODUCTION
Dissimilatory Fe(III) and Mn(IV) reduction refers to the process in which microorganisms reduce Fe(III) or Mn(IV) for purposes other than assimilation of iron or manganese. The ability of microorganisms to reduce Fe(III) or Mn(IV) has been known since early in the 20th century (Harder, 1919; Allison and Scarseth, 1942). However, the capacity for some microbes to conserve energy to support growth via the oxidation of hydrogen (Balashova and Zavarzin, 1980) or organic compounds (Lovley et al.,
Pristine Sediments, Soils, and Subsurface Environments
One of the primary reasons for investigating the physiology of any organism is to better understand its influence on the environments in which it is found and to gain insight into what environmental factors control its growth and activity. Microbial Fe(III) and Mn(IV) reduction are important processes in a diversity of anoxic environments in which organic matter and/or hydrogen as well as Fe(III) and Mn(IV) are available. For example, Fe(III) and Mn(IV) reduction are responsible for the
Microorganisms that Do Not Conserve Energy to Support Growth from Fe(III) Reduction
A wide phylogenetic diversity of microorganisms is known to reduce Fe(III) and Mn(IV) in a dissimilatory manner. Many of these microorganisms reduce Fe(III) as a minor side reaction in their metabolism but do not appear to conserve energy to support growth from this electron transfer (Lovley, 1987, 1991). Extensive lists of such microorganisms are available in previous reviews (Lovley, 1987, 2000b). Many of the initial concepts of the physiology of dissimilatory Fe(III) reduction, such as the
PHYSIOLOGICAL DIVERSITY
There are significant differences in the metabolic capabilities of dissimilatory Fe(III) reducers, which are important to consider in relating the physiology of these organisms to their function in the environment and in predicting the activity of Fe(III) reducers under various environmental conditions.
MECHANISMS FOR Fe(III) AND Mn(IV) REDUCTION
Unlike commonly considered electron acceptors such as oxygen, nitrate, sulfate, or carbon dioxide, Fe(III) and Mn(IV) are highly insoluble in most environments at circumneutral pH. Soluble electron acceptors can diffuse into cells in order to be reduced whereas Fe(III) and Mn(IV) reducers face the challenge of how to transfer electrons onto an insoluble, extracellular, electron acceptor. This is also a challenge for investigators of this process as working with insoluble electron acceptors
CONCLUSIONS
The current understanding of the physiology of dissimilatory Fe(III)- and Mn(IV)-reducing microorganisms suggests that some of these organisms are well adapted for survival and growth in a diversity of environments in which organic matter and/or hydrogen are available as electron donors where Fe(III) or Mn(IV) is present. In addition to playing an important role in the natural cycle of carbon and metals, Fe(III)- and Mn(IV)-reducing microorganisms appear to be useful tools for the
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