The Significance of Yeast Extract Composition on Metabolite Production in Penicillium
In the literature and in our own experience, significant variations occur in morphological characteristics and production of secondary metabolites by cultures grown on YES (2% yeast extract and 15% sucrose) agar, a substrate which is often used in screening for mycotoxins in moulds. In this investigation we have demonstrated a very significant influence of yeast extract brand (Difco, Sigma Y4000 and Y0325, Oxoid, Merck, Lab M and Gibco) on the production of mycotoxins in YES by some important Penicillia. Using a TLC screening method the variation in mycotoxin production due to the use of different brands of yeast extract ranged between detection in 5 days and none detected in 4 weeks. The difference in mycotoxin production was often accompanied by differences in several other characteristics like pH changes of the substrate, sporulation, colony diameter and reverse colour. We have been unable to find which components in the yeast extracts were responsible for the observed changes, but the addition of MgSO4 appeared to be a satisfactory compensation in most respects. So it is suggested that this compound in general is added to the YES formula, along with previously suggested compounds like ZnSO4 and CuSO4, thus making this substrate a very valuable and reliable tool in screening for production of secondary metabolites and in mould taxonomy. Further it is suggested to use pH registration monitoring in the cultures parallel to screening for secondary metabolites, since pH differences proved to be a useful indication of significant changes in the detected profiles.
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