Molecular ecology of aspergillus section flavi species : approaches to understand the role of aflatoxin genes in aflatoxin biosynthesis

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dc.contributor.advisor Magan, Naresh
dc.contributor.advisor Carter, David
dc.contributor.author Abdel-Hadi, Ahmed
dc.date.accessioned 2011-06-23T08:44:39Z
dc.date.available 2011-06-23T08:44:39Z
dc.date.issued 2011-02
dc.identifier.uri http://dspace.lib.cranfield.ac.uk/handle/1826/5571
dc.description.abstract This is the first study to integrate and correlate the effect of ecophysiological factors on the life cycle of Aspergillus flavus by carrying out complementary work on gene expression of the aflatoxin gene cluster, with growth, sporulation and phenotypic toxin production. This information was used to understand the role of ecological factors on key biosynthetic genes and examine the use of such information for control of aflatoxin production using RNA interference. Ecological studies showed the profiles for growth, sporulation and aflatoxin B1 (AFB1) production with optimum ranges of water activity (aw) and temperature for AFB1 production being identified. A. flavus grew faster at 0.99 aw at all temperatures, but optimally at 30-35°C. The highest amount of asexual conidia was produced at 0.95 aw followed by 0.90 aw and then 0.99 aw at all temperatures examined. Interestingly, the partitioning of AFB1 into biomass, medium and spores showed that at 0.99 aw, about 50% of the mycotoxin was present in the biomass and the medium, with very little present in the spores. However, as water stress was imposed there was a switch to a significantly higher channelling of AFB1 (about 45%) into the spores, especially at 0.95 and 0.93 aw levels. A microarray analysis was used to examine the effect of aw x temperature interactions on the relative expression of the aflatoxin gene cluster for the first time using A. flavus NRRL 3357. This showed that under mild stress conditions (20°C/0.99 aw) several of the cluster genes, in particular aflS and aflJ, were highly induced concomitant with high levels of phenotypic AFB1 production. Highest amounts of AFB1 were produced in all conditions where aflS expression was elevated. When the ratio between the normalised expression data of the aflS/aflR genes was generated, high ratios were obtained at 25°C and 30°C at 0.99 and 0.95 aw and low ratios at 25°C and 30°C at 0.90 aw. This is in agreement with the AFB1 production profile. Cont/d. en_UK
dc.language.iso en en_UK
dc.publisher Cranfield University en_UK
dc.rights © Cranfield University 2011. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. en_UK
dc.title Molecular ecology of aspergillus section flavi species : approaches to understand the role of aflatoxin genes in aflatoxin biosynthesis en_UK
dc.type Thesis or dissertation en_UK
dc.type.qualificationlevel Doctoral en_UK
dc.type.qualificationname PhD en_UK


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