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

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.地杆菌属（Geobacter）物种在环境科学与生物技术应用领域备受关注，因其可将电子直接转移至不溶性金属或其他微生物，且具备同化无机碳的能力。本研究报道了还原亚铁地杆菌GS-15（Geobacter metallireducens GS-15）实现二氧化碳固定（CO₂ fixation）以及向铁传递电子的代谢能力与关键代谢调控机制。研究构建了更新版代谢重建模型（metabolic reconstruction），针对预设目标条件开展了生长筛选实验，并采用基于约束的分析方法（constraint-based analysis）对还原亚铁地杆菌GS-15中的关键代谢通路与反应进行了表征与评估。本研究预测并通过体内实验（in vivo）验证了还原亚铁地杆菌GS-15以甲酸盐（formate）与三价铁（Fe(III)）为底物进行自养生长的全新代谢能力。此外，本研究通过系统分离并分析电子传递链（electron transport chain）的不同组分，结合以三种不同外源电子受体（Fe(III)、硝酸盐（nitrate）与延胡索酸盐（fumarate））开展的生长实验，明确了向外源电子受体传递电子的能量消耗。该更新版代谢重建模型将作为知识库，为地杆菌属及类似物种的机制解析与工程化改造提供支撑。