Further Characterization of a Caffeine-Resistant Mutant of Aspergillus parasiticus

Studies were performed to characterize further Aspergillus parasiticus BCR1, a caffeine-resistant mutant of A. parasiticus NRRL 2999, particularly in regard to its caffeine-dependent production of aflatoxins. The enhanced synthesis of aflatoxins by caffeine was highly specific since neither dimethylxanthines nor purines could substitute for the trimethylxanthine. Caffeine's effects were phase dependent and only increased toxin formation if added early in the microorganism's life cycle. The ability of BCR1 to exclude caffeine appeared dependent on the initial levels of caffeine in the growth medium. Respiration and glucose utilization in the wild type strain were inhibited strongly by caffeine, but BCR1 was resistant to these effects. Comparison of glucose uptake kinetics in the wild type and mutant strains indicated that caffeine inhibition of aflatoxin synthesis in the wild type was not due to a disruption of glucose transport.