Production of the mycotoxin patulin in nature.

A study was made of the factors governing the production of the mycotoxin patulin in nature, including biological and physiological factors. The objective of the research described in this thesis was to study the ability of the indigenous fungi of fruits and the apple rot fungus, Penicillium expansum, to grow and to produce patulin in different substrates, both natural (apples, sugar beet, wheat straw) and laboratory media. The effect of carbon and nitrogen sources and the relationship between the production of the toxin and nitrification and its action with the natural isolated bacteria and fungi was also investigated. Common members of the genus Penicillium were found to represent a high percentage of the indigenous fungal flora isolated from both apples and sugar beet. Most of these isolates were able to produce patulin in Czapek Dox liquid medium. Although both apple fruit and sugar beet were naturally highly contaminated with moulds, only apples were contaminated with patulin (7598 gg kg"). Confirmatory tests showed patulin production of 8.3% and 50% (after 7 days) to 99.2% (after 30 days) by the indigenous fungi in apple and sugar beet, respectively. The indigenous fungal flora of wheat straw failed to produce patulin when growing naturally. Patulin was produced only by Penicillium expansum alone and not when growing in association with the white rot fungus Phanerochaete chrysosporium. The accumulation of ammonium and nitrate during urea hydrolysis and ammonium nitrification by Penicillium sp (1), Penicillium sp (3) and Penicillim expansum was achieved with varying degree of efficiency. Urea hydrolysis, but not ammonium nitrification was associated with patulin production. Growth of P. expansum and Penicillium species (1 and 3) occurred under oligotrophic conditions. Both carbon and nitrogen are required for patulin production but it is the depletion of nitrogen which is important for production of the toxin.