Toxic effects of aflatoxin B1 on Bacillus brevis.

At a concentration of 50 microgram/ml and below, aflatoxin B1 inhibited Bacillus brevis (2611) bacteristatically, but at a concentration of 100 microgram/ml the inhibition was bactericidal. Bactericidal inhibition was further studied by determining the mean single survivor times of the bacterium in 100 microgram/ml aqueous solutions of aflatoxin B1 (18.2 mins.) and phenol (16.6 mins.). Further study on the bacteriostatic inhibition within the bacteriostatic concentration limit of 50 microgram/ml shows that the doubling time of B. brevis exposed to 5 microgram/ml aflatoxin B1 is approximately half that of the bacterium exposed to 10 microgram/ml. At the molecular level, 50 microgram/ml aflatoxin B1 inhibited the synthesis of DNA (78%), RNA (15%) and Protein (18%) in B. brevis. The strength of the affinity of subcellular fractions of B. brevis for aflatoxin B1 during inhibition was studied by assessing the resistance of aflatoxin B1 bound to cell fractions to removal by water. 66% (w/w) of the aflatoxin B1 bound to B. brevis after six successive washes in 50 ml distilled water, remained bound to the cell membrane fraction. The implication of this preferential strong binding to cell membrane was studied by investigating its effect on oxygen uptake. Results of inhibition of oxygen uptake is compatible with aflatoxin B1 binding to cell membrane. Vitamin k, however, reversed this inhibition.