Detoxification of aflatoxin B1 by certain bacterial species isolated from Egyptian soil

Aflatoxin contamination of food and grain poses a serious economic and health problem worldwide. Aflatoxin B 1 (AFB 1 ) is extremely mutagenic, toxic and a potent carcinogen to both humans and livestock. A safe, effective and environmentally sound detoxification method is needed for controlling this toxin. In this study, 21 soil samples were screened from various sources with vast microbial populations using a coumarin containing medium. Eleven bacterial isolates showing AFB 1 reduction activity in a liquid culture medium were selected from the screening experiments. Isolate 12-3 and 12-5, obtained from soil samples of Kafr-Zaiat Pesticide company drainage and identified to be Pseudomonas putida and Escherichia coli , reduced AFB 1 by 69.3% and 58.8%, respectively, after incubation in the liquid medium at 37 °C for 72 h. The culture supernatant of these isolates was able to reduce AFB 1 effectively by 76.2% and 62.5%, respectively, whereas the viable cells and cell extracts were far less effective. Factors influencing AFB 1 detoxification by the culture supernatant were investigated. The highest detoxification activity for P. putida and E. coli was 83.3% and 63.8%, respectively, at pH 8 and 30 °C for 72 h. The detoxification activity was reduced at 10, 20 and 45 °C. The Mg 2+ , Mn 2+ , Se and Cu 2+ ions were activators for AFB 1 detoxification. However, Zn 2+ ion was a strong inhibitor. Treatments with proteinase K, proteinase K plus SDS and heating significantly reduced or eradicated the detoxification activity of the culture supernatant. In conclusion, the detoxification of AFB 1 by P. putida 12-3 was enzymatic and the enzymes responsible for the detoxification of AFB 1 are constitutively extracellular produced. Also, the AFB 1 detoxification by E. coli was conducted by enzymes as well as by cell wall binding mechanism. Both bacteria could have great potential in industrial applications.