Stimulation by Hyphopichia burtonii and Bacillus amyloliquefaciens of aflatoxin production by Aspergillus flavus in irradiated maize and rice grains.

Aspergillus flavus was grown on maize and rice extract agars and on irradiated viable cracked maize and rice grains, either in pure culture or in dual culture with wild strains of either Hyphopichia burtonii or Bacillus amyloliquefaciens. Aflatoxin production by A. flavus and its growth and interactions with the other microorganisms were studied at three water activities (aw) (0.98, 0.95, and 0.90) and two temperatures (25 and 16 degrees C). Both H. burtonii and B. amyloliquefaciens markedly stimulated growth and aflatoxin production by A. flavus on cracked maize, especially at 25 degrees C and 0.95 and 0.98 aw. No aflatoxin was detected in pure cultures of A. flavus on cracked rice after 12 days of incubation at 25 degrees C, but some was produced by mixed cultures at 16 degrees C and 0.98 aw. The morphological interactions among A. flavus, H. burtonii, and B. amyloliquefaciens were also examined on maize and rice extract agars under similar controlled conditions.