Multi-omics analysis reveals propanol is superior electron donor for odd-chain elongation

Chain elongation from organic wastes has primarily targeted even-chain carboxylates, leaving the production of equally valuable odd-chain compounds underexplored. Propanol, abundant in industrial wastewater, offers a promising electron donor to address this gap, yet the underlying metabolic pathways and microbial consortia driving efficient odd-chain elongation remain unclear. The present study systematically investigated the characteristics of odd-chain elongation. The results demonstrated that the propanol-acetate (PA) group, using propanol as the electron donor and acetate as the electron acceptor, achieved an excellent selectivity of 84% for n-valerate and n-heptanoate, compared with 55% in the conventional ethanol-propionate (EP) group. Multi-omics analysis guided the specialized metabolic route construction, showing that electrons from propanol oxidation are channeled to drive acetyl-CoA synthesis from acetate and activate the reverse β-oxidation pathway. The propionate generated from propanol oxidation serves as the initial three-carbon backbone for odd-chain carboxylates generation. The keystone microorganisms for propanol-based odd-chain elongation are suggested to be Clostridium kluyveri and Oscillibacter valericigenes. Techno-economic analysis confirmed the metabolic selectivity inherent to the PA group confers superior economic resilience, yielding higher profitability than the EP group. This work positions propanol-based chain elongation as an efficient and economically viable strategy for the targeted production of valuable odd-chain carboxylates from propanol-containing wastewater.