Exploration of Pseudomonas knackmussii AD02 for the biological mitigation of post-harvest aflatoxin contamination: Characterization and degradation mechanism

Aflatoxins, known for their potent carcinogenic and mutagenic properties, pose a major threat to human and animal health. Due to the impacts of climate change, aflatoxin contamination has emerged as a critical food safety issue, necessitating the development of effective detoxification strategies to mitigate its severe health risks. The current isolated, identified, and characterized bacterial strains from peanut-growing soils that are capable of degrading aflatoxin B1 (AFB1). Coumarin was used as a selective carbon source during isolation. Bacterial isolate AD02 had the highest AFB1 degradation efficiency (88.85%). Morphological and genetic analyses confirmed AD02 as a Gram-negative, rod-shaped bacterium closely related to Pseudomonas knackmussii. Optimization studies using a Box-Behnken design showed that initial pH significantly affected AFB1 degradation, with the optimal conditions identified as pH 7, 25 °C, and 24 h of incubation, resulting in approximately 90% AFB1 degradation. Additionally, P. knackmussii AD02 simultaneously degraded a mixture of AFB1, AFB2, AFG1, and AFG2. A mechanistic study of AFB1 degradation revealed the role of extracellular enzymes, particularly in proteinaceous and membrane-associated components. The mechanism for AFB1 degradation involved the hydrolytic cleavage of the lactone ring in the coumarin moiety, followed by the cleavage of the cyclopentenone ring and the elimination of double bonds in the furan and coumarin moieties. The in silico predictions indicated that this bacterium could metabolize AFB1 into a non-mutagenic and non-carcinogenic intermediate product. This study represents the first report on aflatoxin degradation by P. knackmussii, highlighting its potential as an effective biological agent for aflatoxin detoxification.