Transcriptome Sequencing Revealed an Inhibitory Mechanism of Aspergillus flavus Asexual Development and Aflatoxin Metabolism by Soy-Fermenting Non-Aflatoxigenic Aspergillus.

Kunlong Yang,Shihua Wang,Tianran Hu,Xiaona He,Qingru Geng,Jun Tian,Fengqin Song

doi:10.3390/ijms21196994

Abstract

Aflatoxins (AFs) have always been regarded as the most effective carcinogens, posing a great threat to agriculture, food safety, and human health. Aspergillus flavus is the major producer of aflatoxin contamination in crops. The prevention and control of A. flavus and aflatoxin continues to be a global problem. In this study, we demonstrated that the cell-free culture filtrate of Aspergillus oryzae and a non-aflatoxigenic A. flavus can effectively inhibit the production of AFB1 and the growth and reproduction of A. flavus, indicating that both of the non-aflatoxigenic Aspergillus strains secrete inhibitory compounds. Further transcriptome sequencing was performed to analyze the inhibitory mechanism of A. flavus treated with fermenting cultures, and the results revealed that genes involved in the AF biosynthesis pathway and other biosynthetic gene clusters were significantly downregulated, which might be caused by the reduced expression of specific regulators, such as AflS, FarB, and MtfA. The WGCNA results further revealed that genes involved in the TCA cycle and glycolysis were potentially involved in aflatoxin biosynthesis. Our comparative transcriptomics also revealed that two conidia transcriptional factors, brlA and abaA, were found to be significantly downregulated, which might lead to the downregulation of conidiation-specific genes, such as the conidial hydrophobins genes rodA and rodB. In summary, our research provides new insights for the molecular mechanism of controlling AF synthesis to control the proliferation of A. flavus and AF pollution.

Highlights

Aspergillus flavus is a common saprophytic fungus that contaminates many important seed crops, including peanuts, corn, and pistachios [1,2]
The results showed that the total biomass of the co-culture system displayed no difference compared to the wild type (Figure 1B), while A. flavus co-cultivated with A. oryzae was greater in mycelium pellets compared with the wild-type control, and smaller ones were found when co-cultured with TSJ-1 (Figure 1A)
The experiment that A. flavus co-cultivated with different concentrations of spores of A. oryzae/TSJ-1 demonstrated that an increasing conidia amount to 106 of the non-aflatoxigenic Aspergillus strains could apparently block Aflatoxin B1 (AFB1) accumulation (Figure 1C)

Summary

Introduction

Aspergillus flavus is a common saprophytic fungus that contaminates many important seed crops, including peanuts, corn, and pistachios [1,2]. The contamination of A. flavus causes huge economic losses to agricultural production across the world This fungus is an opportunistic pathogen for immunocompromised patients, which is the second most common cause of aspergillosis after A. fumigatus [3]. Several biological control strategies to reduce AF contamination have been developed, including the use of non-toxic A. flavus and other fungi to inhibit aflatoxin synthesis [13]. A previous study reported that spreading non-toxic A. parasiticus strains on peanut-growing soil could reduce the AF content in edible peanuts by 83% to 98% [15]. Fungi, such as white-rot fungus, Rhizopus pseudomonas, and A. niger, have been utilized to control aflatoxin biosynthesis [16]. Non-toxigenic aspergilli used for fermented foods, such as A. oryzae and A. niger, could be the best prospect for the sake of their safety

Methods

Results

Conclusion