New insights into the interplay between chain elongation and homoacetogenesis in microbial electrosynthesis: Chloroform-enhanced medium-chain carboxylate production.

Microbial electrosynthesis (MES)-assisted chain elongation (CE) is a promising strategy for sustainable medium-chain carboxylic acid (MCCA) production from waste streams. However, MES induces inevitable H2 evolution, and the understudied interaction between H2-driven homoacetogenesis and CE creates a critical knowledge gap. To resolve this metabolic conflict, chloroform (CHCl3) at 0.0075%-0.045% was used to inhibit homoacetogenesis, with systematic investigations on carbon flux distribution, functional microbial communities, and key metabolic pathways. Results showed 0.03% CHCl3 optimized MCCA production to 2902.8 ± 116.1 mg COD/L (103.0% increase), with electron efficiency (40.8%) and acetate utilization efficiency (94.3%) significantly higher than the Control (21.8% and 43.5%, respectively). Homoacetogenesis inhibition conserved reducing power (moderated H2, lowered NAD+/NADH) and redirected acetyl-CoA to drive CE. Microbial community analysis revealed enriched chain-elongating bacteria with more modular, cooperative interaction networks. Metagenomic analysis confirmed elevated abundances of reverse β-oxidation genes (e.g., ACAT, crt) and reduced homoacetogenesis genes (e.g., cooF, cooS) after treatment. Taxon-function contribution analysis identified Clostridium_kluyveri as the dominant functional agent for CE-related key genes. Economic and life-cycle assessments demonstrated a net economic gain of $1.61-4.22/m3 and mitigated key environmental impacts due to improved product yield. This study elucidates how regulating the competition between homo-acetogens and chain-elongating bacteria directionally enhances CE, providing a novel ecological perspective and strategy for optimizing electricity-driven biomanufacturing processes.