Abstract
Food and feed contamination by aflatoxin (AF)B&sub1; has adverse economic and health consequences. AFB&sub1; degradation by microorganisms or microbial enzymes provides a promising preventive measure. To this end, the present study tested 43 bacterial isolates collected from maize, rice, and soil samples for AFB&sub1;-reducing activity. The higher activity was detected in isolate L7, which was identified as Bacillus shackletonii. L7 reduced AFB&sub1;, AFB&sub2;, and AFM&sub1; levels by 92.1%, 84.1%, and 90.4%, respectively, after 72 h at 37 °C. The L7 culture supernatant degraded more AFB&sub1; than viable cells and cell extracts; and the degradation activity was reduced from 77.9% to 15.3% in the presence of proteinase K and sodium dodecyl sulphate. A thermostable enzyme purified from the boiled supernatant was designated as Bacillus aflatoxin-degrading enzyme (BADE). An overall 9.55-fold purification of BADE with a recovery of 39.92% and an activity of 3.85 × 10³ U·mg-1 was obtained using chromatography on DEAE-Sepharose. BADE had an estimated molecular mass of 22 kDa and exhibited the highest activity at 70 °C and pH 8.0, which was enhanced by Cu2+ and inhibited by Zn2+, Mn2+, Mg2+, and Li⁺. BADE is the major protein involved in AFB&sub1; detoxification. This is the first report of a BADE isolated from B. shackletonii, which has potential applications in the detoxification of aflatoxins during food and feed processing.