The role of microorganisms in the reduction of solid phase iron minerals and corrosion of ferrous metals entails fundamental mechanisms which have common grounds for both processes. In each case, organisms influence surface/liquid interracial reactions and are responsible for accelerating oxidation- or reduction-coupled mineral/metal dissolution. Hydrogen is a widely used microbial energy source which can serve as an electron donor to drive microbial iron reduction or accelerate the rate of the cathodic reaction during anaerobic corrosion. In the former, bacteria act as a biocatalyst to promote a thermodynamically favorable reaction in which the cells directly control electron flow. In the latter,
microorganisms serve to remove a reaction product to permit continuation of an abiotic reaction, thereby, indirectly accelerating the overall reaction sequence. Bacterial mediated dissolution of base
metals and metal oxides essentially may be governed by identical rate limiting processes. Mass transfer-limited processes apply both in bioreduction of iron mineral complexes and in biooxidation of corrodible
metals, hence, the accumulation of end products near or on surfaces acts to impede microbial reactions. For example, concentration polarization of an electrode is a well established corrosion phenomenon. An analogous situation may occur during the bioreduction of hematite by dissimilatory iron reducing bacteria. The manner in which microbes influence the rates and possibly the extent of biotic reactions on
metals is of practical interest in the fields of bioremediation and corrosion control.