Role of Polyphenols from the Aqueous Extract of Aloysia citrodora in the Inhibition of Aflatoxin B1 Synthesis in Aspergillus flavus.

Aflatoxin B1 (AFB1) is a mycotoxin considered a potent carcinogen for humans that contaminates a wide range of crops. Various strategies have been established to reduce or block the synthesis of AFB1 in food and feed. The use of aqueous extracts derived from plants with high antioxidant activity has been a subject of study in recent years due to their efficacy in inhibiting AFB1. In this study, we assessed the effect of Aloysia citrodora aqueous extract on Aspergillus flavus growth and on AFB1 production. A bio-guided fractionation followed by High Performance Liquid Chromatography (HPLC) and Mass spectrometry analysis of the active fraction were applied to identify the candidate molecules responsible for the dose-effect inhibition of AFB1 synthesis. Our results revealed that polyphenols are the molecules implicated in AFB1 inhibition, achieving almost a total inhibition of the toxin production (99%). We identified luteolin-7-diglucuronide as one of the main constituents in A. citrodora extract, and demonstrated that it is able to inhibit, by itself, AFB1 production by 57%. This is the first study demonstrating the anti-Aflatoxin B1 effect of this molecule, while other polyphenols surely intervene in A. citrodora anti-AFB1 activity.

Aspergillus korhogoensis, a Novel Aflatoxin Producing Species from the Côte d'Ivoire.

Several strains of a new aflatoxigenic species of Aspergillus, A. korhogoensis, were isolated in the course of a screening study involving species from section Flavi found contaminating peanuts (Arachis hypogaea) and peanut paste in the Côte d'Ivoire. Based on examination of four isolates, this new species is described using a polyphasic approach. A concatenated alignment comprised of nine genes (ITS, benA, cmdA, mcm7, amdS, rpb1, preB, ppgA, and preA) was subjected to phylogenetic analysis, and resulted in all four strains being inferred as a distinct clade. Characterization of mating type for each strain revealed A. korhogoensis as a heterothallic species, since three isolates exhibited a singular MAT1-1 locus and one isolate exhibited a singular MAT1-2 locus. Morphological and physiological characterizations were also performed based on their growth on various types of media. Their respective extrolite profiles were characterized using LC/HRMS, and showed that this new species is capable of producing B- and G-aflatoxins, aspergillic acid, cyclopiazonic acid, aflavarins, and asparasones, as well as other metabolites. Altogether, our results confirm the monophyly of A. korhogoensis, and strengthen its position in the A. flavus clade, as the sister taxon of A. parvisclerotigenus.

Piperine inhibits aflatoxin B1 production in Aspergillus flavus by modulating fungal oxidative stress response.

Aspergillus flavus, a soil-borne pathogen, represents a danger for humans and animals since it produces the carcinogenic mycotoxin Aflatoxin B1 (AFB1). Approaches aiming the reduction of this fungal contaminant mainly involve chemicals that may also be toxic. Therefore, identification and characterization of natural anti-aflatoxigenic products represents a sustainable alternative strategy. Piperine, a major component of black and long peppers, has been previously demonstrated asan AFB1-inhibitor; nevertheless its mechanism of action was yet to be elucidated. The aim of the present study was to evaluate piperine's molecular mechanism of action in A. flavus with a special focus on oxidative stress response. For that, the entire AFB1 gene cluster as well asa targeted gene-network coding for fungal stress response factors and cellular receptors were analyzed. In addition to this, fungal enzymatic activities were also characterized. We demonstrated that piperine inhibits aflatoxin production and fungal growth in a dose-dependent manner. Analysis of the gene cluster demonstrated that almost all genes participating in aflatoxin's biosynthetic pathway were down regulated. Exposure to piperine also resulted in decreased transcript levels of the global regulator veA together with an over-expression of genes coding for several basic leucine zipper (bZIP) transcription factors such as atfA, atfB and ap-1 and genes belonging to superoxide dismutase and catalase's families. Furthermore, this gene response was accompanied by a significant enhancement of catalase enzymatic activity. In conclusion, these data demonstrated that piperine inhibits AFB1 production while positively modulating fungal antioxidant status in A. flavus.