Browsing by Author "Schmidt-Heydt, Markus"

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    Complex regulation of the aflatoxin biosynthesis gene cluster of Aspergillus flavus in relation to various combinations of water activity and temperature
    (Elsevier, 2009-11-15) Schmidt-Heydt, Markus; Abdel-Hadi, Ahmed; Magan, Naresh; Geisen, Rolf
    A microarray analysis was performed to study the effect of varying combinations of water activity and temperature on the activation of aflatoxin biosynthesis genes in Aspergillus flavus grown on YES medium. Generally A. flavus showed expression of the aflatoxin biosynthetic genes at all parameter combinations tested. Certain combinations of aw and temperature, especially combinations which imposed stress on the fungus resulted in a significant reduction of the growth rate. At these conditions induction of the whole aflatoxin biosynthesis gene cluster occurred, however the produced aflatoxin B1 was low. At all other combinations (25 °C/0.95 and 0.99; 30 °C/0.95 and 0.99; 35 °C/0.95 and 0.99) a reduced basal level of cluster gene expression occurred. At these combinations a high growth rate was obtained as well as high aflatoxin production. When single genes were compared, two groups with different expression profiles in relation to water activity/temperature combinations occurred. These two groups were co-ordinately localized within the aflatoxin gene cluster. The ratio of aflR/aflJ expression was correlated with increased aflatoxin biosynthesis.
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    Modelling the relationship between environmental factors, transcriptional genes and deoxynivalenol mycotoxin production by strains of two Fusarium species
    (2011-01-06T00:00:00Z) Schmidt-Heydt, Markus; Parra, Roberto; Geisen, Rolf; Magan, Naresh
    The effect of changes in temperature/water activity (a(w)) on growth, deoxynivalenol (DON) production and trichothecene gene cluster expression (18 genes) for strains of Fusarium culmorum and Fusarium graminearum was studied. The expression data for six key transcription genes (TRI4, TRI5, TRI6, TRI10, TRI12 and TRI13) were analysed using multiple regression analyses to model the relationship between these various factors for the first time. Changes in a(w) and temperature significantly (p=0.05) affected growth and DON. Microarray data on expression of these genes were significantly related to DON production for both strains. Multi-regression analysis was done and polynomial models found to best fit the relationship between actual/predicted DON production relative to the expression of these TRI genes and environmental factors. This allowed prediction of the amounts of DON produced in two-dimensional contour maps to relate expression of these genes to either a(w) or temperature. These results suggest complex interactions between gene expression (TRI genes), environmental factors and mycotoxin production. This is a powerful tool for understanding the role of these genes in relation to environmental factors and enables more effective targeted control strategies to be developed.
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    The production of aflatoxin B1 or G1 by Aspergillus parasiticus at various combinations of temperature and water activity is related to the ratio of aflS to aflR expression
    (Mycotoxin Research, 2010-11-01T00:00:00Z) Schmidt-Heydt, Markus; Rüfer, C. E.; Abdel-Hadi, Ahmed; Magan, Naresh; Geisen, Rolf
    The influence of varying combinations of wateractivity (aw) and temperature on growth, aflatoxin biosynthesisand aflR/aflS expression of Aspergillus parasiticuswas analysed in the ranges 17-42°C and 0.90-0.99 aw.Optimum growth was at 35°C. At each temperature studied,growth increased from 0.90 to 0.99 aw. Temperatures of 17and 42°C only supported marginal growth. The externalconditions had a differential effect on aflatoxin B1 or G1biosynthesis. The temperature optima of aflatoxin B1 andG1 were not at the temperature which supported optimalgrowth (35°C) but either below (aflatoxin G1, 20-30°C) orabove (aflatoxin B1, 37°C). Interestingly, the expression ofthe two regulatory genes aflR and aflS showed anexpression profile which corresponded to the biosynthesisprofile of either B1 (aflR) or G1 (aflS). The ratios of theexpression data between aflS:aflR were calculated. Highratios at a range between 17 and 30°C corresponded withthe production profile of aflatoxin G1 biosynthesis. A lowratio was observed at >30°C, which was related to aflatoxinB1 biosynthesis. The results revealed that the temperaturewas the key parameter for aflatoxin B1, whereas it waswater activity for G1 biosynthesis. These differences inregulation may be attributed to variable conditions of theecological niche in which these specie
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    A systems approach to model the relationship between aflatoxin gene cluster expression, environmental factors, growth and toxin production by Aspergillus flavus.
    (2012-04-07T00:00:00Z) Abdel-Hadi, Ahmed; Schmidt-Heydt, Markus; Parra, Roberto; Geisen, Rolf; Magan, Naresh
    A microarray analysis was used to examine the effect of combinations of water activity (a(w), 0.995-0.90) and temperature (20-42°C) on the activation of aflatoxin biosynthetic genes (30 genes) in Aspergillus flavus grown on a conducive YES (20 g yeast extract, 150 g sucrose, 1 g MgSO(4)·7H(2)O) medium. The relative expression of 10 key genes (aflF, aflD, aflE, aflM, aflO, aflP, aflQ, aflX, aflR and aflS) in the biosynthetic pathway was examined in relation to different environmental factors and phenotypic aflatoxin B(1) (AFB(1)) production. These data, plus data on relative growth rates and AFB(1) production under different a(w) × temperature conditions were used to develop a mixed-growth-associated product formation model. The gene expression data were normalized and then used as a linear combination of the data for all 10 genes and combined with the physical model. This was used to relate gene expression to a(w) and temperature conditions to predict AFB(1) production. The relationship between the observed AFB(1) production provided a good linear regression fit to the predicted production based in the model. The model was then validated by examining datasets outside the model fitting conditions used (37°C, 40°C and different a(w) levels). The relationship between structural genes (aflD, aflM) in the biosynthetic pathway and the regulatory genes (aflS, aflJ) was examined in relation to a(w) and temperature by developing ternary diagrams of relative expression. These findings are important in developing a more integrated systems approach by combining gene expression, ecophysiological influences and growth data to predict mycotoxin production. This could help in developing a more targeted approach to develop prevention strategies to control such carcinogenic natural metabolites that are prevalent in many staple food products. The model could also be used to predict the impact of climate change on toxin production.