Abstract
Metals are essential for life and the so-called transition metals undergo redox transformations on a biologically accessible potential range. These transformations have an impact in their mobility in aqueous medium, their bioavailability, their toxicity, and their affinity for biological macromolecules. Extracellular redox chemistry is therefore an essential process for the interaction between living organisms and metals. In this chapter we present a survey of the current state of the art with respect to the molecular mechanisms of microbial assimilatory metal uptake with an emphasis for iron. Direct metal uptake by membrane transporters and indirect metal uptake by metallophores are presented. The molecular mechanisms of dissimilatory metal reduction with emphasis for iron and manganese reducers are also described. The modes of extracellular electron transfer are presented in general and then exemplified with the molecular mechanisms known for Gram-negative and Gram-positive bacteria. The implications of the extracellular redox chemistry of microorganisms for the environment, health, and biotechnology are discussed at the end of the chapter and these are framed in the context of the open questions that guide future research directions and reveal new possibilities for diverse applications.
