The effect of elevated temperature on gene transcription and aflatoxin biosynthesis

Abstract

The molecular regulation of aflatoxin biosynthesis is complex and influenced by several environmental conditions; one of these is temperature. Aflatoxins are produced optimally at 28-30 C, and production decreases as temperatures approach 37 C, the optimum temperature for fungal growth. To better characterize the influence of temperature on aflatoxin biosynthesis, we monitored the accumulation of aflatoxin and the expression of more than 5000 genes in Aspergillus flavus at 28 C and 37 C. A total of 144 genes were expressed differentially (P < 0.001) between the two temperatures. Among the 103 genes more highly expressed at 28 C, approximately 25% were involved in secondary metabolism and about 30% were classified as hypothetical. Genes encoding a catalase and superoxide dismutase were among those more highly expressed at 37 C. As anticipated we also found that all the aflatoxin biosynthetic genes were much more highly expressed at 28 C relative to 37 C. To our surprise expression of the pathway regulatory genes aflR and aflS, as well as aflR antisense, did not differ between the two temperatures. These data indicate that the failure of A. flavus to produce aflatoxin at 37 C is not due to lack of transcription of aflR or aflS. One explanation is that AFLR is nonfunctional at high temperatures. Regardless, the factor(s) sensing the elevated temperatures must be acute. When aflatoxin-producing cultures are transferred to 37 C they immediately stop producing aflatoxin.

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

“…Various ecophysiological studies with A. flavus (Sorensen et al 1967;Gqaleni et al 1997;O'Brian et al 2007;Schmidt-Heydt et al 2009) have been done, but much less information is available for A. parasiticus (Lin et al 1980;Faraj et al 1991;Park and Bullerman 1981).…”

Genetic regulation of aflatoxin biosynthesis: From gene to genome

“…A total of 136 genes were differentially expressed between the two strains . Included in these differentially expressed genes were gene products that were regulated in other array experiments by O'Brian et al (2007) and Wilkinson et al (2007) such as the AAA family ATPase (clone NAF-BE02TV), two different conidiation-specific proteins (clones NAG-DC44TV and NAFEY43TV), and a Rieske 2Fe-2S family-like protein (clone NAFCL17TV). Many of the genes in the AF cluster were similarly affected when compared to prior array experiments (Fig.…”

Fungal endophytes and bioprospecting

“…It is important to screen fungal species for their secondary metabolite spectrum under different growth conditions; culture parameters such as composition of growth medium, aeration, pH and the presence of certain enzyme inhibitors change dramatically the secondary metabolite profile and even induce the synthesis of several new metabolites (Bode et al, 2002). For example in Aspergillus flavus, the genes involved in secondary metabolism show higher levels of expression at 28 C than at 37 C (OBrian et al, 2007).…”