Bio-solubilization of Yunnan lignite by Penicillium ortum MJ51 and characterization of its products

•Strain MJ51 could solubilize 82.0% of pretreated lignite within 8 days.•Multiple extracellular substances mediate the solubilization of lignite.•Strain MJ51 can rebuild the intermolecular hydrogen bonding of lignite.•Strain MJ51 can introduce C=O into the structure of coal in the same way as HNO3.•Black liquid fractions contained various aromatic and aliphatic compounds.