Abstract: Nicotine-degrading bacteria are functional microorganisms capable of using nicotine as the sole carbon and nitrogen source, showing considerable potential for nicotine removal and aroma modulation. In recent years, advances in molecular biology and genomics have progressively clarified the mechanisms of microbial nicotine catabolism, and four major metabolic modes have been recognized: the pyridine pathway, the pyrrolidine pathway, a hybrid/variant mode featuring characteristics of both pathways (the VPP-type pathway), and the fungal methylation pathway. This review summarizes the taxonomic characteristics of representative nicotine-degrading microorganisms, the key catabolic routes and enzymes, and the mechanistic links and molecular regulatory networks connecting nicotine degradation with aromatization-related transformations. In addition, we outline recent progress and remaining challenges in the application of these microorganisms to inoculation-based tobacco fermentation. Overall, this work provides a theoretical basis and technical reference for nicotine biodegradation research and greener processing strategies in the tobacco industry.