Milestone 6.8 Advanced understanding mechanisms of aflatoxin biosynthesis in A. flavus infecting almond under stress conditions (Rapporti progetti di ricerca)

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  • Milestone 6.8 Advanced understanding mechanisms of aflatoxin biosynthesis in A. flavus infecting almond under stress conditions (Rapporti progetti di ricerca) (literal)
Anno
  • 2011-01-01T00:00:00+01:00 (literal)
Alternative label
  • Antonia Gallo, Filomena Epifani, Giancarlo Perrone, Michele Solfrizzo e Giuseppe Panzarini (2011)
    Milestone 6.8 Advanced understanding mechanisms of aflatoxin biosynthesis in A. flavus infecting almond under stress conditions
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  • Antonia Gallo, Filomena Epifani, Giancarlo Perrone, Michele Solfrizzo e Giuseppe Panzarini (literal)
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  • Milestone 6.8 del progetto Europeo MycoRed (literal)
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  • 17 (literal)
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  • Istituto di Scienze delle Produzioni Alimentari ISPA - CNR (literal)
Titolo
  • Milestone 6.8 Advanced understanding mechanisms of aflatoxin biosynthesis in A. flavus infecting almond under stress conditions (literal)
Abstract
  • The molecular regulation of aflatoxin biosynthesis is complex and influenced by several environmental conditions. A lot of studies have been conducted on the variation of the capability of aflatoxin production in A. flavus, when an abiotic stress is applied. In the current study, for the first time, the influence of two important factors, such as water activity and temperature, was evaluated during the infection of almond by A. flavus. To this aim an agarized almond medium was used and the expression of some of the aflatoxin biosynthetic genes was analysed during the fungal growth. The best growth rate, in terms of quantity of fungal biomass, and the higher production of AFB1 were observed when A. flavus grew at 28°C and at aw value of medium set at 0.96, even though the accumulation process was slower and the maximum was reached later in comparison with 0.99 aw. Both an increase and a reduction of temperature cause a lowering of AFB1 production when the medium presents a aw standard condition (0.99), with the higher temperature (37°C) affecting more than the low temperature (20°C). Likewise, at standard conditions of temperature (28°C) the decrease of aw at the lowest values results in a remarkable loss of production capability. In Fig. 6 the concurrent effects of the two factors considered in this work is represented. When the two parameters are contemporaneously changed, their influence is greater, so that at 0.96 aw and at 20°C mycotoxin production is reduced compared to 0.99 aw at the same temperature. When the aw is set at the lowest values (0.93 and 0.90 aw), the growth is completely inhibited at 20°C, while at 37°C the production is repressed at 0.90 aw, and at 0.93 aw is slightly higher than at 0.96 aw. It can be observed how, with a prolonged time of incubation, the risk of OTA contamination can increase with lowering of aw values. Regarding the expression of biosynthetic genes, the evidence is that at optimal conditions of production (0.96 and 0.99 aw, and 28°C) the two regulatory genes (aflR and aflS) are activated at their highest levels in the early days, much more and sooner than the structural ones, which show a maximum level of transcription, even greater than aflR and aflS, just before the peak of AFB1 accumulation. Generally, when conditions become unfavourable for aflatoxin production, the expression levels decrease, above all those of structural genes which never exceed the levels of aflR and aflS. The regulatory genes are always expressed, also when no AFB1 accumulation is detected, and with the lowering of aw, in the very early days of fungal growth, even in a greater manner than at more favourable conditions, Moreover, at 28°C with the decrease of aw, the ratio of expression aflR:aflS is higher than at optimal conditions at the beginning of incubation. In addition, when the conditions become less permissive, this ratio is subject to notable fluctuations with the passage of time, while when temperature and aw values are most favourable for AFB1 production, the ratio tends to change in a lesser extent. This aspect is worth of further investigation to better understand the mechanism of regulation based on the two genes of aflatoxin cluster. (literal)
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