ROLE OF COMPETITION AND ADVERSE CULTURE CONDITIONS IN PREVENTING THE LOSS OF A AFLATOXIN PRODUCTION BY ASPERGILLUS FLAVUS DURING SERIAL TRANSFERS

Authors: Horn, Bruce; Dorner, Joe

Submitted to: Mycopathologia
Publication Type: Abstract Only
Publication Acceptance Date: 10/24/2001
Publication Date: 1/10/2002
Citation: Horn, B.W., Dorner, J.W. 2002. Role of competition and adverse culture conditions in preventing the loss of a aflatoxin production by aspergillus flavus during serial transfers. Mycopathologia.

Interpretive Summary: Not required on "abstract only".

Technical Abstract: Aspergillus flavus is genetically unstable when repeatedly transferred in culture. Serial transfers often result in loss of aflatoxin production and in associated morphological changes such as reduced sporulation, proliferation of aerial hyphae and an inability to produce sclerotia. However, degeneration does not readily occur in nature as indicated by the wild-type morphological characters of newly isolated strains and the high percentage of aflatoxigenic A. flavus from soil and crops in some geographic regions. In this study, three aflatoxin-producing strains of A. flavus were serially transferred using conidia for 20 generations (three independent generation lines per strain) on potato dextrose agar at 30 C. The rate of degeneration was compared to that of cultures grown under adverse conditions (elevated temperature, reduced water activity, low pH and nutrient deprivation) and in the presence of competing fungi (A. terreus, Penicillium funiculosum and the yeast, Pichia guilliermondii). The loss of aflatoxin production over generations varied considerably according to strain and the generation line within each strain. In the strain most sensitive to degeneration on potato dextrose agar, aflatoxin-producing ability was maintained to varying degrees under adverse culture conditions but not when A. flavus was competing with other fungi. Examination of single-spore isolates from cultures following serial transfers indicated that conidial populations comprised a mixture of wild-type aflatoxin producers and variant colony types that were low or nonproducers of aflatoxin B1. Therefore, reduction in aflatoxin production over successive generations in the laboratory may be interpreted on a population level in which selection favors variant nonaflatoxigenic individuals. In populations from nature, adverse environmental conditions may instead select for wild-type individuals and remove variant individuals that are observed only in the laboratory.