Conductive Materials in Microbial Chain Elongation for Medium-Chain Fatty Acids Biosynthesis: A Critical Review of Mechanisms and Metabolic Regulation

Abstract

Microbial chain elongation, which uses anaerobic fermentation to produce high-value medium-chain fatty acids (MCFAs), is a promising strategy for resource sustainability, yet its efficacy is limited by poor extracellular electron transfer and thermodynamic imbalances in chain elongation (CE) microbiomes. This review provides a multidimensional perspective on how conductive materials─including carbon-based materials, iron-based materials, and engineered composites─reshape the energy metabolism network to drive efficient MCFAs biosynthesis. The physicochemical properties of these materials systematically determine their electron-mediating capacities, forming dynamic conductive networks that boost electron transfer. Moreover, the significant intracellular metabolic adaptations linked to these materials are critically examined, encompassing modulation of the NAD+/NADH balance, shifts in ATP synthesis, and the associated upregulation of key enzymes within the reverse β-oxidation and fatty acid biosynthesis pathways. Synergistic integration with electro-fermentation and biofilm reactors is highlighted, demonstrating process intensification and enhanced operational robustness. Finally, scalability and sustainability are evaluated through techno-economic analysis and life-cycle assessment, identifying critical challenges and opportunities for industrial translation. By synthesizing mechanistic insights with engineering perspectives, this review proposes a “material-electron transfer-metabolism-engineering” framework to guide the rational design and scalable application of conductive materials for next-generation waste valorization.