Constraint-Based Modeling of Carbon Fixation and the Energetics of Electron Transfer in <i>Geobacter metallireducens</i>

<div><p><i>Geobacter</i> species are of great interest for environmental and biotechnology applications as they can carry out direct electron transfer to insoluble metals or other microorganisms and have the ability to assimilate inorganic carbon. Here, we report on the capability and key enabling metabolic machinery of <i>Geobacter metallireducens</i> GS-15 to carry out CO₂ fixation and direct electron transfer to iron. An updated metabolic reconstruction was generated, growth screens on targeted conditions of interest were performed, and constraint-based analysis was utilized to characterize and evaluate critical pathways and reactions in <i>G. metallireducens</i>. The novel capability of <i>G. metallireducens</i> to grow autotrophically with formate and Fe(III) was predicted and subsequently validated <i>in vivo</i>. Additionally, the energetic cost of transferring electrons to an external electron acceptor was determined through analysis of growth experiments carried out using three different electron acceptors (Fe(III), nitrate, and fumarate) by systematically isolating and examining different parts of the electron transport chain. The updated reconstruction will serve as a knowledgebase for understanding and engineering <i>Geobacter</i> and similar species.</p>