Biodegradation of oxidized lignite by Pseudomonas sp. TX1: Degradation products and metabolomic characterization.

Microbial degradation offers a green pathway for resource recovery and clean conversion of low-rank coal. However, the mechanisms governing the extracellular depolymerization of coal macromolecules and intracellular metabolic regulation remain poorly understood. This study integrated solid-phase structural characterization, liquid-phase product analysis, and untargeted metabolomics to investigate lignite biodegradation by an indigenous isolate, Pseudomonas sp. TX1. During TX1 treatment of oxidized lignite, the culture supernatant reached an absorbance at 450 nm (A450) of 2.67 after 10 days, indicating the accumulation of colored soluble components. The strain preferentially cleaves methylene bridges and alkyl side chains in lignite, followed by biological funneling of highly substituted aromatic rings into ring-opened intermediates. GC-MS analysis demonstrated that lignite was successfully depolymerized into high-value liquid-phase small molecules with broad industrial applications, including long-chain alkanes, fatty acid methyl esters, phenolic derivatives, and nitrogen-containing heterocycles. Metabolomic analysis revealed that aromatic monomers undergo ring-opening metabolism via the homogentisate and β-ketoadipate pathways. Concurrently, the pentose phosphate pathway is activated to supply reducing power, while ascorbic acid and melatonin cycles are regulated to counteract oxidative stress. This study elucidates the multi-scale molecular mechanism of coal biotransformation, providing a theoretical basis for developing low-rank coal bioconversion technologies.