SUMMARY: A study was made of the binding of aflatoxin B and its toxic effects on NRRL B-1368. After a 12 hr incubation period, 5 μg. aflatoxin Bm1. inhibited growth of the test organism 95 %. Viable organisms decreased from 3.8 × 10/ml. in the controls to 5.0 × 10/ml. in a growth medium containing 50 μg. aflatoxin B/ml., after 4 hr. of incubation. Viability was not significantly decreased, however, when the organisms were incubated with the same concentration of toxin either under nitrogen, or at 5°, or in the presence of bacteriostatic concentrations of tetracycline. Binding experiments showed that 4.0 × 10 organisms/ml. took up approximately 7.0 μg. aflatoxin B/ml. After five aqueous washes of the organisms, 20-25% of the toxin remained bound to them. The tightly bound toxin was removed by ultrasonic treatment of the organisms and chloroform extraction of the macerate. Removal of cell walls by lysozyme following toxin uptake released 23% of the initially bound toxin, and osmotic rupture of the protoplasts an additional 7%. Toxin was also taken up by intact and by ruptured protoplasts. Removal of nucleic acids from the membranes did not alter their capacity to bind aflatoxin B.


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