Thermophilic keystone taxa drive humification in coal gangue co-composting via shikimate-pathway carbon flux.

Co-composting of coal gangue and organic solid waste is an effective resource utilization method, but systematic understanding of the humification process in co-composting systems remains limited. The study systematically investigated the evolution of humic substances in a coal gangue co-composting system and identified the roles of thermophilic keystone taxa by machine learning models combined with metagenomic analysis in the humification process. The results indicate that maintaining the thermophilic phase is crucial for humification in the coal gangue co-composting system. Experimental groups that maintained a stable thermophilic phase achieved complete humification and produced compost that effectively promoted wheatgrass growth on sandy soil. The key thermophiles (Thermobifida, Thermopolyspora, and Planifilum) are significantly associated with humic substances and the shikimate pathway. These bacteria support the humification process by enhancing the synthetic potential of the shikimate pathway, thereby providing the necessary supply of aromatic precursor substances. This study elucidates the humification process in the coal gangue co-composting and identifies the role of key thermophiles, providing theoretical and practical guidance for the bioutilization of coal gangue and the improvement of desertified soils.