Electronic Bifurcation: A New Perspective on Fe Bio-Utilization in Anaerobic Digestion of Lactate

Anaerobic microorganisms use flavin/quinone-based electronicbifurcation(EB) to gain a survival advantage at the thermodynamic limits. However,the contribution of EB to microscopic energy and productivity in theanaerobic digestion (AD) system is unknown. This study demonstratesfor the first time that under limited substrate conditions, Fe-drivenEB in AD leads to a 40% increase in specific methane production andcontributes to 25% ATP accumulation, by analyzing the concentrationof EB enzymes such as Etf-Ldh, HdrA(2)B(2)C(2), and Fd, NADH and actual Gibbs free-energy changes.Differential pulse voltammetry and electron respiratory chain inhibitionexperiments detected that iron enhanced electron transport in EB byaccelerating the activity of flavin, Fe-S clusters, and quinonegroups. Other microbial and enzyme genes with EB potential closelyrelated to iron transport have also been found in metagenomes. Thepotential of EB to accumulate energy and enhance productivity in ADsystems was investigated, and metabolic pathways were proposed inthe study. Based on the energy-savingcharacteristics of electronicbifurcation (EB), a strategy of strengthening anaerobic digestioncapacity of iron-driven multi-EB in the restricted environment isproposed.