Synergy among multiple electron donors in electro-fermentation chain elongation: Accelerated directional electron transfer and enhanced microbial functions.

Electro-fermentation assisted chain elongation (EF_CE) effectively converts organic waste into medium-chain fatty acids (MCFAs), yet the regulatory mechanisms involving multiple electron donors (EDs) require elucidation. This study systematically explored the synergistic effects of ethanol and lactate as EDs on MCFA biosynthesis in EF_CE systems. The cross-niche microbial associations shaped by multiple EDs coupled with inoculation with caproate-synthesizing bacteria led to a 2.9-3.9-fold increase in caproate synthesis. Metagenomic analysis revealed that multiple EDs decreased the relative abundances of genes encoding Mut in the acrylate pathway, while increasing the relative abundances of genes encoding ascB in the Wood-Ljungdahl pathway, and ADH, kor and cdhA in ethanol and lactate oxidation pathways. These findings highlight the dual role of EDs synergy in directing MCFAs production and reshaping microbial networks, offering insights for improving organic waste/wastewater recycling.