Aflatoxin B <inf>1</inf> degradation by Stenotrophomonas maltophilia and other microbes selected using coumarin medium

Aflatoxin B 1 (AFB 1) is one of the most harmful mycotoxins in animal production and food industry. A safe, effective and environmentally sound detoxification method is needed for controlling this toxin. In this study, 65 samples were screened from various sources with vast microbial populations using a newly developed medium containing coumarin as the sole carbon source. Twenty five single-colony bacterial isolates showing AFB 1 reduction activity in a liquid culture medium were selected from the screen. Isolate 35-3, obtained from tapir feces and identified to be Stenotrophomonas maltophilia, reduced AFB 1 by 82.5% after incubation in the liquid medium at 37°C for 72 h. The culture supernatant of isolate 35-3 was able to degrade AFB 1 effectively, whereas the viable cells and cell extracts were far less effective. Factors influencing AFB 1 degradation by the culture supernatant were investigated. Activity was reduced to 60.8% and 63.5% at 20°C and 30°C, respectively, from 78.7% at 37°C. The highest degradation rate was 84.8% at pH 8 and the lowest was only 14.3% at pH 4.0. Ions Mg 2+ and Cu 2+ were activators for AFB 1 degradation, however, ion Zn 2+ was a strong inhibitor. Treatments with proteinase K, proteinase K plus SDS and heating significantly reduced or eradicated the degradation activity of the culture supernatant. The results indicated that the degradation of AFB 1 by S. maltophilia 35-3 was enzymatic and could have a great potential in industrial applications. © 2008 by the authors; licensee Molecular Diversity Preservation International.