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|Document Type: ||Thesis or dissertation|
|Title: ||Molecular ecology of aspergillus section flavi species : approaches to understand the role of aflatoxin genes in aflatoxin biosynthesis|
|Authors: ||Abdel-Hadi, Ahmed|
|Supervisors: ||Magan, Naresh|
|Issue Date: ||Feb-2011|
|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
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
|Appears in Collections:||PhD, EngD and MSc by research theses (Cranfield Health) |
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