Fe(III) and Mn(IV) Reduction

Abstract

This chapter summarizes the known environmental consequences of Fe(III) respiration as well as related forms of respiration such as reduction of Mn(IV) and humic substances. The finding that specialized microorganisms are capable of Fe(III)-based respiration substantially changed the understanding of iron geochemistry in soils and sediments. The concept of metal-based respiration has been expanded from Fe(III) to a wide variety of redox-active metals and metalloids that have now been found to serve as terminal electron acceptors in microbial respiration. The chapter provides a brief overview of the major groups of Fe(III)-reducing microorganisms that grow at circumneutral pH. Sedimentation of soils naturally high in Fe(III) or Mn(IV) may also enhance Fe(III) and Mn(IV) reduction in aquatic sediment. Reoxidation of Fe(II) and Mn(II) produced as the result of Fe(III) and Mn(IV) reduction can also be an important source of Fe(III) and Mn(IV) for microbial reduction. It is apparent that more research is required to better understand the mechanisms for Fe(III) oxide reduction by Fe(III)-respiring microorganisms (FRM) in pure culture, but elucidating the pathways for Fe(III) reduction in soils and sediments may be even more difficult. Further investigation into the biochemical and biogeochemical mechanisms of Fe(III) and Mn(IV) reduction is required in order to fully realize the potential of these processes for environmental remediation.