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

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.

Genetic Responses and Aflatoxin Inhibition during Co-Culture of Aflatoxigenic and Non-Aflatoxigenic Aspergillus flavus

“…Genes in the early and middle portions of the aflatoxin biosynthesis pathway were downregulated in NRRL 3357 in response to A. oryzae filtrates [60]. The aflatoxin biosynthetic pathway-specific co-activator, aflS, was substantially downregulated, but there was not significantly less expression of the transcriptional activator aflR [60]. Contrary to our findings, there was greater expression of imizoquins and cyclopiazonic acid upon exposure to only culture filtrates [60].…”

“…During co-culture, it is impossible to rule out that inhibition of aflatoxin production is only due to outcompeting the Tox isolate by the Non-tox isolate since here Tox 53 grew substantially less than Non-tox 17. However, cell-free Non-tox media filtrates from A. flavus, including Non-tox 17 and A. oryzae, inhibited aflatoxin production [37][38][39][40]60] or degraded aflatoxin [41]. Genes in the early and middle portions of the aflatoxin biosynthesis pathway were downregulated in NRRL 3357 in response to A. oryzae filtrates [60].…”

“…However, cell-free Non-tox media filtrates from A. flavus, including Non-tox 17 and A. oryzae, inhibited aflatoxin production [37][38][39][40]60] or degraded aflatoxin [41]. Genes in the early and middle portions of the aflatoxin biosynthesis pathway were downregulated in NRRL 3357 in response to A. oryzae filtrates [60]. The aflatoxin biosynthetic pathway-specific co-activator, aflS, was substantially downregulated, but there was not significantly less expression of the transcriptional activator aflR [60].…”

Quantitative Proteomic Analysis for High- and Low-Aflatoxin-Yield Aspergillus flavus Strains Isolated From Natural Environments

“…We postulated that these up-regulated hydrophobins could help the A . flavus strains isolated from natural environments invade crops and thereafter produce more AFs ( Chang et al, 2012 ; Yang et al, 2020 ). In addition, it has been reported that vacuole-associated proteins can promote AF synthesis in fungi and also promote the consequent export of AFs by regulating vacuolar homeostasis ( Chanda et al, 2009 ; Yang et al, 2021 ).…”

Aflatoxin Detoxification Using Microorganisms and Enzymes

“…Transcriptome sequencing has shown that some genes such as AflS, FarB, and MtfA are involved in the biosynthetic pathway of AFs. The synthetic gene cluster was significantly down-regulated, and the two conidial transcription factors BrlA and AbaA were significantly down-regulated, which may down-regulate conidia-specific genes (such as the conidial hydrophobin genes RodA and RodB) [ 91 ].…”