The Biochemistry of Dissimilatory Ferric Iron and Manganese Reduction in Shewanella oneidensis

More than two decades ago, Kenneth Nealson and Charles Myers published a seminal manuscript, describing an organism that can couple growth to the respiratory reduction of manganese oxide, an extracellular electron acceptor. This was the starting point of research aiming to elucidate mechanisms of extracellular respiration in a γ-proteobacterium named Shewanella oneidensis. This research is manifested in a nearly confusing multitude of publications that are sometimes even contradictory. It is the aim of this chapter to give a thorough overview of our knowledge about the biochemistry of metal respiration in S. oneidensis. This chapter starts off with a technological survey describing the molecular toolbox we have in our hands to genetically modify S. oneidensis. Thereafter, the path of electrons from the cytoplasmic membrane to the cell surface is followed, and thereby potential proteins for this electron transport and the transfer onto terminal metallic electron acceptors are brought to the reader’s attention. Moreover, the potential role of further proteins is analyzed that are not necessarily involved in the electron transport chain to ferric iron or manganese oxides per se but still seem to provide a selective advantage for the organism. Throughout the text it will become clear that the list of open questions concerning S. oneidensis physiology is still, even after decades of research and although it is the best studied dissimilatory metal reducer, extensive, and that there is room for more fascinating questions that can be addressed using the system S. oneidensis.