Aflatoxin B 1 effects on soil microorganisms

Abstract

Corn contaminated with aflatoxin is unfit for consumption by animals and is most often disposed of by plowing it into the soil. The effect of aflatoxin B 1 on the population and activity of soil microorganisms was determined at concentrations of 1, 100 and 10,000 ng ml −1 of agar media or g −1 of soil. Aflatoxin B 1 at 10,000 ng ml −1 of medium reduced the number of viable fungi by 38% and the number of bacteria and actinomycetes by 34%. Soil amended to 10,000 ng aflatoxin B 1 demonstrated a slight, yet significant reduction in the population of fungi and bacteria plus actinomycetes. At this rate the antagonistic effect on soil microorganisms began at 14 days after aflatoxin B 1 was added and lasted nearly 6 weeks. Subsequently no significant differences were observed among any of the treatments. When the soil was amended with alfalfa to provide a substrate for microbial growth, the population showed a more significant reduction due to aflatoxin B 1, but the duration of the effect was reduced. The evolution of CO 2 from soil amended with aflatoxin B 1 showed little if any diminution. Similarly, aflatoxin B 1 failed to demonstrate a significant effect on nitrifying bacteria. Aflatoxin B 1 was found to be slightly deleterious to Rhizobium japonicum, resulting in a 30% reduction in numbers at the highest treatment rate. Using auxotrophic cultures of R. japonicum, aflatoxin B 1 was also shown to induce the formation of mutants.