Isolation and characterization of a Bacillus subtilis strain with aflatoxin B1 biodegradation capability

Aflatoxins are type of mycotoxins mainly produced by Aspergillus flavus and a common contaminant of food and grain, posing a serious economic and health problem worldwide. In order to find efficient bacteria to remove or detoxify these mycotoxins, a bacterial strain capable of degrading aflatoxin B₁ (AFB₁) was isolated from soil samples using a culture medium containing coumarin as the sole carbon source. Based on 16S rRNA gene sequence analysis, this isolate was identified as Bacillus subtilis JSW-1; its further characterization showed that it could inhibit the growth of A. flavus with an inhibition ratio of 58.3% and could degrade AFB₁ by 67.2% after incubation at 30 °C for 72 h. The aflatoxin B₁-degrading activity of isolate JSW-1 was predominantly attributed to the cell-free supernatant and this activity was found to be heat stable but sensitive to proteinase K treatment, indicating that the extracellular proteins or enzymes are responsible for the AFB₁ degradation. In addition, no degradation products of AFB₁ could be detected by liquid chromatography-mass spectrometry (LC-MS) analysis, indicating that the parent AFB₁ might be biotransformed to compounds with chemical properties different from that of AFB₁.