This work unveiled the neglected role and mechanism of rhamnolipid (RL) in modulating microbial interspecies electron transfer for SSA during MSW anaerobic fermentation.
Synchronous sulfidogenesis and acidogenesis (SSA) is critical for pollutant removal and resource recovery. However, inefficient electron transfer and metabolic imbalance between acidogenic bacteria and sulfidogens limited SSA performance, especially from mariculture solid wastes (MSW) containing high-strengthen sulfate. This work unveiled the neglected role and mechanism of rhamnolipid (RL) in modulating microbial interspecies electron transfer for SSA during MSW anaerobic fermentation. RL at environmentally relevant levels of 20-200 mg/g suspended solids, simultaneously improved sulfide production (40.1-87.9%) and short-chain fatty acids yield (8.0-19.3 folds). Extracellular polymeric substances (EPSs) exhibited higher capacitance and electroactivity to store or transfer electrons in presence of RL. Proper RL facilitated redox mediator secretion and mediated a faster one-electron transfer via flavins/Cytochrome c combination. Binding experiments and molecular simulations further revealed that RL increased dipole moment of a-helix peptide and spontaneously interacted with C=O of amide groups, which enabled efficient electron hopping in EPSs. RL also activated intracellular electron transfer system, delivering more electrons flow to sulfate reductase through Nicotinamide adenine dinucleotide?Flavin mononucleotide?Fe-S clusters?Coenzyme Q. Metagenomic analysis verified differential enrichment of microorganisms and key genes upregulation related with SSA, EPSs secretion, quorum sensing, energy synthesis, conductive pili and electron shuttles synthesis. These findings deepen our understanding of biosurfactant-modulated electron transfer in anaerobic environment.