Analysis of the effect of nutritional factors on OTA and OTB biosynthesis and polyketide synthase gene expression in Aspergillus ochraceus Abdelhamid Abbas a , Heriberto Valez a , Alan D.W. Dobson a,b, ⁎ a Department of Microbiology, University College Cork, Cork, Ireland b Environmental Research Institute, University College Cork, Cork, Ireland abstract article info Article history: Received 16 March 2009 Received in revised form 1 July 2009 Accepted 14 July 2009 Keywords: Ochratoxin A Ochratoxin B Transcriptional regulation 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. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Ochratoxin A (OTA) is one of the most common naturally occurring mycotoxins and is found in a variety of grain crops such as barley, corn, wheat, rye and oats (Jorgensen and Jacobsen, 2002). It is produced by both Aspergillus ochraceus and Penicillium verrucosum, with the former being the most common OTA producer in tropical regions of the world; while the latter tends to predominate in more temperate regions, such as north eastern and eastern Europe (Sweeney and Dobson, 1998). Other Aspergilli which produce OTA include Aspergil- lus carbonarius, which typically affects wine grapes and Aspergillus alliaceus which contaminates nuts and figs (Bayman et al., 2002). Other Penicillium strains which produce OTA include Penicillum nordicum, which appears to be particularly adapted to spoilage in the food environment, such as fermented meats and cheeses; unlike P. verrucosum which almost exclusively spoils stored cereals (Lund and Frisvad, 2003). OTA is considered a serious health hazard to humans as it possesses nephrotoxic, hepatotoxic, teratogenic, carcinogenic, antibiotic and immunotoxic properties. Humans can be exposed to OTA if they consume contaminated foods of plant based origin. Food products derived from animals that have been fed mould contaminated feed or fodder also represent an important source of contamination to humans (Bragulat et al., 2008; Kabak et al., 2006). The OTA biosynthetic pathway has not as yet been fully biochemically or genetically elucidated despite the cloning of OTA polyketide synthase genes from several fungi species including A. ochraceus (O'Callaghan et al., 2003), Aspergillus westerdijkiae (Bacha et al., 2009) and P. nordicum (Karolewiez and Geisen, 2005). OTA is a hybrid molecule composed of a type 1 polyketide dihydroiso-coumarin moiety, linked via an amide bond to the amino acid, phenylalanine (Ferriera and Pitout,1969; Steyn and Holzapfel, 1970; Moss 1998). The phenylalanine moiety is synthesized via the shikimic acid pathway and is likely to be linked to the chlorinated dihydroiso-coumarin at carbon 10; a step which is most likely to involve a non-ribosomal peptide synthase (NRPS) (Ferriera and Pitout, 1969; Harris and Mantle, 2001). Ochratoxin B (OTB), is the nonchlorinated analogue of OTA, with the same molecular structure as OTA but lacking a chlorine in the C5 position of the molecule. OTB may be produced by the same biosynthetic pathway as OTA, without the chlorination step, which is believed to be catalysed by a chloroper- oxidase (Harris and Mantle, 2001; Lee et al., 2007). OTB has recently been reported to be produced in A. alliaceus, A. auricomus and A. sclerotiorum (Lee et al., 2007). It has also been reported that OTβ (a putative intermediate in the OTA biosynthetic pathway) can be transformed into OTA and OTB in the ratio of 1:5 in favour of OTA, while the transformation of OTB into OTA can also occur but at a much lower level (Harris and Mantle, 2001). International Journal of Food Microbiology 135 (2009) 22–27 ⁎ Corresponding author. Environmental Research Institute, University College Cork, Lee Road, Cork, Ireland. Tel.: +353 214901946. E-mail address: a.dobson@ucc.ie (A.D.W. Dobson). 0168-1605/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2009.07.014 Contents lists available at ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro