Abstract
Geobacter 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 Geobacter metallireducens 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 G. metallireducens. The novel capability of G. metallireducens to grow autotrophically with formate and Fe(III) was predicted and subsequently validated in vivo. 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 Geobacter and similar species.
Highlights
Microorganisms play a major role in the global carbon cycle
Insights into the various mechanisms and energetic constrains which govern their behavior will advance our understanding of carbon fluxes and might allow for a rational perturbation of the carbon cycle
We further discover a novel growth condition which enables the characterization of autotrophic metabolism in Geobacter
Summary
Microorganisms play a major role in the global carbon cycle. Insights into the various mechanisms and energetic constrains which govern their behavior will advance our understanding of carbon fluxes and might allow for a rational perturbation of the carbon cycle. Qualitative and quantitative knowledge of carbon assimilation and electron flow to and from key microorganisms is critical when evaluating certain aspects of the carbon cycle. Quantitative assessment of carbon and energy flow in G. metallireducens by computational modeling approaches provides valuable insight into the role of this bacterium in the carbon cycle. Geobacter species play a major role in the biogeochemical cycling due to their ability to couple the oxidation of organic compounds to the reduction of Fe(III) and Mn(IV) oxides [5]. Direct electron transfer from electrodes to microorganisms to drive anaerobic respiration has potential applications in bioenergy and bioremediation [7]. Metabolic network reconstruction (the most widely utilized form of COBRA) enables the enumeration of the genome-wide machinery (i.e., enzymes, uptake systems, etc.) in an organized fashion for use in modeling [9]. A validated and accurate network can be utilized for prospective design and engineering of cellular networks [10]
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