Abstract
Aflatoxin B1 (AFB1), the predominant and most carcinogenic naturally polyketide, is mainly produced by Aspergillus flavus and Aspergillus parasiticus. Cinnamaldehyde has been reported for inhibiting the growth and aflatoxin biosynthesis in A. flavus. But its molecular mechanism of action still remains largely ambiguous. Here, the anti-aflatoxigenic mechanism of cinnamaldehyde in A. flavus was investigated via a comparative transcriptomic analysis. The results indicated that twenty five of thirty genes in aflatoxin cluster showed down-regulation by cinnamaldehyde although the cluster regulators aflR and aflS were slightly up-regulated. This may be due to the up-regulation of the oxidative stress-related genes srrA, msnA and atfB being caused by the significant down-regulation of the diffusible factor FluG. Cinnamaldehyde also inhibited aflatoxin formation by perturbing GPCRs and oxylipins normal function, cell wall biosynthesis and redox equilibrium. In addition, accumulation of NADPH due to up-regulation of pentose phosphate pathway drove acetyl-CoA to lipids synthesis rather than polyketides. Both GO and KEGG analysis suggested that pyruvate and phenylalanine metabolism, post-transcriptional modification and key enzymes biosynthesis might be involved in the suppression of AFB1 production by cinnamaldehyde. This study served to decipher the anti-aflatoxigenic properties of cinnamaldehyde in A. flavus and provided powerful evidence for its use in practice.
Highlights
Aspergillus flavus, as a widely distributed saprotrophic filamentous fungus especially in warmer and moister atmosphere, is the major safety problem in both agricultural and medical products[1]
Production of aflatoxin B1 (AFB1) was completely inhibited by cinnamaldehyde at lower concentration (0.4 mM) without influencing A. flavus growth, and at the concentration of 0.8 mM cinnamaldehyde showed complete inhibition of fungal growth and AFB1 production[1]. This was similar to the results reported by Sun[8], which indicated that fungal growth and aflatoxin production were significantly inhibited by cinnamaldehyde in dose-dependent manner by modulating the oxidative stress in A. flavus
From the expression profile data, we found that the expression patterns of some gene referred to conidiophores development were down-regulated when A. flavus was treated with cinnamaldehyde (Table S3)
Summary
Aspergillus flavus, as a widely distributed saprotrophic filamentous fungus especially in warmer and moister atmosphere, is the major safety problem in both agricultural and medical products[1]. Cinnamaldehyde, a major component of Chinese cinnamon oil from Cinnamomum spp, is used as legally flavoring antimicrobial ingredient and referenced as “generally recognized as safe” for mankind and surroundings by the USFDA and FAO/WHO8 It has been widely used in food, booze to inhibit the growth of bacteria, yeast and filamentous fungi because of the wider spectrum antimicrobial activities since long time[9,10]. This was similar to the results reported by Sun[8], which indicated that fungal growth and aflatoxin production were significantly inhibited by cinnamaldehyde in dose-dependent manner by modulating the oxidative stress in A. flavus It takes inhibitory action against bacteria[11,18,19], yeast and filamentous molds[20,21,22] by depressing intracellular ATP23, cell wall biosynthesis[24], and altering the membrane structure and integrity
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