Abstract
Aflatoxin is a mycotoxin and a secondary metabolite, and the most potent known liver carcinogen that contaminates several important crops, and represents a significant threat to public health and the economy. Available approaches reported thus far have been insufficient to eliminate this threat, and therefore provide the rational to explore novel methods for preventing aflatoxin accumulation in the environment. Many terrestrial plants and microbes that share ecological niches and encounter the aflatoxin producers have the ability to synthesize compounds that inhibit aflatoxin synthesis. However, reports of natural aflatoxin inhibitors from marine ecosystem components that do not share ecological niches with the aflatoxin producers are rare. Here, we show that a non-pathogenic marine bacterium, Vibrio gazogenes, when exposed to low non-toxic doses of aflatoxin B1, demonstrates a shift in its metabolic output and synthesizes a metabolite fraction that inhibits aflatoxin synthesis without affecting hyphal growth in the model aflatoxin producer, Aspergillus parasiticus. The molecular mass of the predominant metabolite in this fraction was also different from the known prodigiosins, which are the known antifungal secondary metabolites synthesized by this Vibrio. Gene expression analyses using RT-PCR demonstrate that this metabolite fraction inhibits aflatoxin synthesis by down-regulating the expression of early-, middle-, and late- growth stage aflatoxin genes, the aflatoxin pathway regulator, aflR and one global regulator of secondary metabolism, laeA. Our study establishes a novel system for generation of aflatoxin synthesis inhibitors, and emphasizes the potential of the under-explored Vibrio’s silent genome for generating new modulators of fungal secondary metabolism.
Highlights
Aflatoxins are a group of secondary metabolites that are synthesized primarily by food-borne fungi such as Aspergillus parasiticus and Aspergillus flavus
As a first step in understanding how V. gazogenes, responds to aflatoxin B1, we investigated the effect of three different doses of aflatoxin B1 on the growth of V. gazogenes
We demonstrate the feasibility of a novel system for generation of aflatoxin biosynthesis inhibitors, a concept that is analogous to the generation of antibodies upon antigen exposure
Summary
Aflatoxins are a group of secondary metabolites that are synthesized primarily by food-borne fungi such as Aspergillus parasiticus and Aspergillus flavus. Common agricultural approaches used for prevention of aflatoxin contamination in crops include use of fungicides, biocontrol agents and fungi-resistant plants, crop rotation, choice of a plantation time that avoids the aflatoxin-conducive climatic conditions, and control of environmental factors during postharvest (Kabak et al, 2006; Wu and Khlangwiset, 2010a,b; Cary et al, 2011). Most of these strategies are expensive, time-consuming and have demonstrated limited success. Development of additional novel methodologies and compounds for aflatoxin elimination is essential
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