The mechanism underlying lignite biodegradation by Cupriavidus sp isolated from sludge

Lignite, a low-rank coal, is commonly utilized as a fuel source. However, its high sulfur and ash content can result in the release of harmful substances during combustion. Microbial coal degradation offers a more environmentally friendly alternative to traditional chemical and physical methods of coal treatment. In this study, we obtained a bacterium, named as Cupriavidus sp isolated from activated sludge that exhibits potential for lignite degradation. After identification via 16S rDNA sequencing, the degradation characteristics and mechanisms of strain S4 on lignite from Shanxi, were systematically evaluated. Extracellular enzyme activities of strain S4 were measured, revealing the secretion of lignin peroxidase, manganese peroxidase, laccase, alkaline protease, and amylase, indicating its capacity for multi-enzyme synergistic degradation. Scanning electron microscopy (SEM) observations confirmed that the bacterium could adsorb onto the coal surface. Fourier transform infrared spectroscopy (FTIR) analysis demonstrated a significant increase in free hydroxyl groups on the coal, which facilitates degradation. Gas chromatography-mass spectrometry (GC-MS) and three-dimensional fluorescence spectroscopy analyses of the liquid-phase products showed a notable increase in long-chain alkanes and phenolic compounds in the degradation liquid, along with the detection of humic substances. Further studies indicated that strain S4 mediates initial adsorption through the secretion of extracellular polymers (EPS) rich in proteins and polysaccharides, highlighting the key mechanism of microbial-coal interface interaction. This study provides a theoretical foundation for the development of lignite bioremediation technologies and the resource-based application of functional bacterial strains.