Microbial Oxidation of Organic Matter Coupled to the Reduction of Fe(III) and Mn(IV) Oxides
Abstract
The studies summarized here have demonstrated that there are microorganisms which can effectively couple the oxidation of organic matter to the reduction of Fe(III) and Mn(IV) oxides. Although individual Fe(III)- or Mn(IV)reducing organisms have restricted substrate ranges, mixed populations of Fe(III)- or Mn(IV)-reducing microorganisms can work in consort to completely oxidize complex assemblages of sediment organic matter. This microbially catalyzed Fe(III) reduction is the only mechanism which has been demonstrated to have the potential to account for the oxidation of organic matter coupled to Fe(III) reduction that is observed in a variety of sedimentary environments. In the wide variety of surface and subsurface aquatic environments that have been examined, Fe(III)-reducing microorganisms have consistently been recovered from environments where this reaction is taking place. Such phenomena as the formation and dissolution of several important iron minerals, the lack of sulfide and methane production in the presence of Fe(III) oxides, the accumulation of high iron concentrations in groundwater, and the oxidation of organic contaminants coupled to Fe(III) reduction can be explained, at least in part, by the physiological characteristics of the Fe(III)-reducing microorganisms. However, microbial Fe(III) and Mn(IV) reduction has received much less attention than other microbial processes in sediments and there are many basic aspects of these processes that are yet to be addressed.
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