Sophorolipid-enhanced methane production from low-rank coal: metagenomic insights into microbial and metabolic mechanisms

Anaerobic digestion (AD) represents a promising approach for enhancing coal resource utilization and advancing sustainable development within the coal industry. This study investigates the role of sophorolipid biosurfactants in enhancing methane production during coal AD. Sophorolipid supplementation significantly increased methane yield by reshaping the microbial community, enriching key bacteria ( Proteiniphilum , Petrimonas ) and methanogens ( Methanobacterium , Methanosarcina ). Metagenomic analysis revealed concurrent upregulation of glycolytic genes and critical pathways for pyruvate-to-acetate conversion ( aceE , PDH , ALDH ) and CO₂ reduction ( fdh , fdo ), driving methanogenesis through both acetoclastic and hydrogenotrophic pathways. Mechanistically, sophorolipid enhanced microbial membrane permeability and upregulated the TolC gene of the bacterial type I secretion system, facilitating extracellular enzyme release and coal depolymerization. These biological effects were complemented by physicochemical changes, including reduced liquid surface tension and increased ζ-potential, which improved microbe–enzyme–coal interactions. Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry confirmed the degradation of aromatic and aliphatic hydrocarbons. Collectively, sophorolipid biosurfactants enhance coal biodegradation efficiency through synergistic microbial, genetic, and interfacial mechanisms, offering a promising strategy for cleaner coal conversion.