Differential Expression of Genes Related to Growth and Aflatoxin Synthesis in Aspergillus flavus When Inhibited by Bacillus velezensis Strain B2

Mechanism Underlying Bacillus subtilis BS-Z15 Metabolite-Induced Prevention of Grain Contamination by Aspergillus flavus

Aspergillus flavus can cause mildew in corn, peanuts, and other foods as well as animal feed, which seriously endangers human and livestock health; thus, preventing A. flavus contamination is imperative. Previous studies have found that the secondary metabolites of Bacillus subtilis BS-Z15 have broad-spectrum-inhibiting fungal activity, further confirming that the main active inhibiting fungal substance is Mycosubtilin (Myco). In this paper, corn and peanuts were treated with 0, 100, and 200 μg/mL BS-Z15 secondary metabolites (BS-Z15-SMA) for 7 days, and the aflatoxin contamination prevention effect was examined. The results showed that with increasing BS-Z15-SMA concentration, the aflatoxin contamination prevention effect was significantly enhanced. The above toxicity phenomena became more significant with extended BS-Z15-SMA treatment time. Scanning electron microscopy showed that 4 μg/mL Myco treatment resulted in a dented A. flavus surface and breakage of both the conidial stem and the mycelium. Transcriptome results showed that Myco significantly affected gene expression in A. flavus spores. The downregulated genes were significantly enriched in cell wall synthesis, transcription and translation, transmembrane transport pathways, and pathways related to key enzymes for aflatoxin synthesis. These results suggest that Myco could be used as a new bioactive material to prevent aflatoxin synthesis and contamination.

Biocontrol Capabilities of Bacillus subtilis E11 against Aspergillus flavus In Vitro and for Dried Red Chili (Capsicum annuum L.)

As a condiment with extensive nutritional value, chili is easy to be contaminated by Aspergillus flavus (A. flavus) during field, transportation, and storage. This study aimed to solve the contamination of dried red chili caused by A. flavus by inhibiting the growth of A. flavus and detoxifying aflatoxin B₁ (AFB₁). In this study, Bacillus subtilis E11 (B. subtilis) screened from 63 candidate antagonistic bacteria exhibited the strongest antifungal ability, which could not only inhibit 64.27% of A. flavus but could also remove 81.34% of AFB₁ at 24 h. Notably, scanning electron microscopy (SEM) showed that B. subtilis E11 cells could resist a higher concentration of AFB₁, and the fermentation supernatant of B. subtilis E11 could deform the mycelia of A. flavus. After 10 days of coculture with B. subtilis E11 on dried red chili inoculated with A. flavus, the mycelia of A. flavus were almost completely inhibited, and the yield of AFB₁ was significantly reduced. Our study first concentrated on the use of B. subtilis as a biocontrol agent for dried red chili, which could not only enrich the resources of microbial strains for controlling A. flavus but also could provide theoretical guidance to prolong the shelf life of dried red chili.