This lecture covers the metabolic diversity of microorganisms, including chemoorganotrophs, chemolithotrophs, phototrophs, and their different electron acceptors. It discusses the role of enzymes as biological catalysts, the redox electron carriers like NAD and FAD, and the process of oxidative phosphorylation. The lecture also delves into the Fe cycle, iron-reducing microorganisms, and the mechanisms of Fe(III) reduction by bacteria like Geobacter and Shewanella. It explores the importance of Fe(III) oxide reduction in anaerobic environments and the electron transfer mechanisms involved. Additionally, it touches on the role of electron shuttles and iron chelators in the reduction of Fe(III) minerals.