Orchestrating Caproate Biosynthesis through Iron–Carbon Microelectrolysis: From Electrochemical Corrosion and Metagenomic Regulation

Abstract

The chain elongation (CE) process for medium-chain fatty acid (MCFA) biosynthesis offers a sustainable strategy for organic waste valorization, yet its efficiency is constrained by suboptimal microbial metabolic activity. To address this limitation, this study developed an iron–carbon (IC) composite material featuring an iron–carbon microelectrolysis effect. IC supplementation significantly augmented carbon flux toward caproate biosynthesis by 27.3%, mediated through four interconnected mechanisms. First, electrochemical corrosion of iron anodes sustained Fe2+ release, which elevated the abundance of genes encoding iron-dependent enzymes involved in the oxidative phosphorylation pathway, enhancing the genetic potential for ATP synthesis and energy metabolism. Second, the carbon cathode facilitated [H] generation through H+ consumption, concurrently driving critical redox cofactors’ regeneration (ferredoxin and NAD(P)H) and stabilizing pH conditions in CE systems. Furthermore, metagenomic analysis revealed that IC amendments enriched functional microorganisms (e.g., Azotobacter_chroococcum and Pseudomonas_sp.) and increased the abundance of CE-associated enzyme genes. Lastly, IC orchestrated ABC transporters and quorum sensing, regulating microbial nutrient uptake, bacterial chemotaxis, and biofilm formation, which fostered interspecies collaboration. This study provided valuable insights into the multilevel regulatory mechanism underlying IC-mediated caproate biosynthesis, establishing a paradigm for optimizing caproate biosynthesis in waste-to-resource applications.