Analysis of the effect of nutritional factors on OTA and OTB biosynthesis and polyketide synthase gene expression in Aspergillus ochraceus.

The effect of a wide variety of nutritional based biotic factors on the production of both OTA and OTB biosynthesis in A. ochraceus was assessed. Different carbon sources including glucose, sucrose, maltose, galactose, xylose and glycerol appear to repress OTA production when the fungus is grown in OTA permissive PDY medium. In contrast lactose appears to induce OTA production, with the addition of lactose and galactose to the OTA restrictive PDC medium resulting in marked increases in OTA levels. The addition of lactose to MCB and PDY media considerably increases OTB production. The addition of both sucrose and galactose to MCB has similar yet less marked effects. Different nitrogen sources also affect OTA production with ammonium chloride significantly reducing OTA production, while organic nitrogen sources such as urea and amino acids including phenylalanine, lysine, glutamine and proline induce OTA production. The induction of otapksAo gene expression under these conditions correlates well with the levels of OTA produced under the same experimental conditions, suggesting that the observed effects appear to be modulated, at least in part, at the level of gene transcription. However while the levels of OTB produced in A. ochraceus also appear to be influenced by these nutritional based biotic factors, this appears to be regulated in a manner which is independent of otapksAo gene expression.