Van Diepingen noticed, though, that Aspergillus niger somehow did manage to 'acquire' more new genetic material than was to be expected given its sexual handicap. She discovered this by screening Aspergilli sorts for the presence of dsRNA mycoviruses. Ten per cent of the sample were infected: strange, as infected Aspergilli should grow less quickly, produce fewer spores and lose the fight against other sorts. If this were the case, then in a fungus population with so little genetic exchange as A. niger, the virus would disappear quickly.

Van Diepeningen calculated that in evolutionary terms it was impossible for the fungi to maintain an infection rate as high as ten per cent. This situation could only be explained if Aspergilli were exchanging genetic material regularly in another way. "And that's what was happening," tells the PhD candidate. "Aspergillus niger exchanges genetic material with other fungus sorts."

Research on the extent of horizontal transfer of genetic material in fungus only started in 1996. "Before then all research was on horizontal DNA transfer in bacteria," recounts Van Diepeningen. The change in focus to fungi stems from the increased interest being shown by industry. The food industry has long used Aspergillus niger. The fungus produces citric acid, used in soft drinks and soya sauce. It is likely that the food industry will start to genetically modify this fungus in the not too distant future. However, a spread of introduced genetic material to wild Aspergillus is not desirable. Van Diepeningen's research is aimed at being able to provide well-founded estimates on the chance of the spread of genetically modified organisms. The candidate herself is reticent about predicting the likely dangers of modifying Aspergilli: "I can only reiterate what I've already written in my thesis."

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