Inhibitory Effects of Eurotium cristatum on Growth and Aflatoxin B1 Biosynthesis in Aspergillus flavus

Assessing the Risk of Exposure to Aflatoxin B1 through the Consumption of Peanuts among Children Aged 6-59 Months in the Lusaka District, Zambia

Aflatoxins B1 (AFB1) are fungi-produced toxins found in crops like peanuts, maize, and tree nuts. They constitute a public health concern due to their genotoxic and carcinogenic effects. A deterministic exposure risk assessment to AFB1 through the consumption of peanuts was conducted on children using the Margin of Exposure (MOE) and the liver cancer risk approaches. Data on AFB1 concentrations in peanuts, quantities of peanut consumption, and the weights of the children were obtained from the literature. Generally, MOE values were below the safe margin of 10,000, ranging between 3.68 and 0.14, 754.34 and 27.33, and 11,428.57 and 419.05 for the high (0.0466 ng/kg), median (0.00023 ng/kg), and low (0.000015 ng/kg) AFB1 concentration levels, respectively. The liver cancer risk upon lifetime exposure to highly AFB1-contaminated peanuts (0.0466 ng/kg) ranged between 1 and 23 (95% lower bound) and 2 and 50 (95% upper bound) cases in a million individuals: a public health concern. A low liver cancer risk (≤1 case in a billion individuals upon lifetime exposure) was shown at median and low AFB1 concentrations. However, the risk of AFB1 should be a priority for risk management since its harmful effects could be potentiated by poor diet, high malnutrition levels, and other disease burdens in Zambia's children.

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.

A New Benzaldehyde Derivative Exhibits Antiaflatoxigenic Activity against Aspergillus flavus

Aflatoxin B1 (AFB1) is the most potent naturally occurring carcinogen for humans and animals produced by the common fungus Aspergillus flavus (A. flavus). Aflatoxin (AF) contamination in commodities is a global concern related to the safety of food and feed, and it also impacts the agricultural economy. In this study, we investigated the AFB1-inhibiting activity of a new benzaldehyde derivative, 2-[(2-methylpyridin-3-yl)oxy]benzaldehyde (MPOBA), on A. flavus. It was found that MPOBA inhibited the production of AFB1 by A. flavus, with an IC50 value of 0.55 mM. Moreover, the inhibition of conidiation was also observed at the same concentration. The addition of MPOBA resulted in decreased transcript levels of the aflR gene, which encodes a key regulatory protein for the biosynthesis of AF, and also decreased transcript levels of the global regulator genes veA and laeA. These results suggested that MPOBA has an effect on the regulatory mechanism of the development and differentiation of conidia, leading to the inhibition of AFB1 production. In addition, the cytotoxicity study showed that MPOBA had a very low cytotoxic effect on the Madin-Darby canine kidney (MDCK) cell line. Therefore, MPOBA may be a potential compound for developing practically effective agents to control AF 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.

PXR as the tipping point between innate immune response, microbial infections, and drug metabolism

Pregnane X receptor (PXR) is a xenosensor that acts as a transcription factor in the cell nucleus to protect cells from toxic insults. In response to exposure to several chemical agents, PXR induces the expression of enzymes and drug transporters that biotransform xenobiotic and endobiotic and eliminate metabolites. Recently, PXR has been shown to have immunomodulatory effects that involve cross-communication with molecular pathways in innate immunity cells. Conversely, several inflammatory factors regulate PXR signaling. This review examines the crosstalk between PXR and nuclear factor kappa B (NFkB), Toll-like receptors (TLRs), and inflammasome components. Discussions of the consequences of these interactions on immune responses to infections caused by viruses, bacteria, fungi, and parasites are included together with a review of the effects of microorganisms on PXR-associated drug metabolism. This paper aims to encourage researchers to pursue studies that will better elucidate the relationship between PXR and the immune system and thus inform treatment development.

Corepressors SsnF and RcoA Regulate Development and Aflatoxin B1 Biosynthesis in Aspergillus flavus NRRL 3357

Aspergillus flavus is a saprophytic fungus that can be found across the entire world. It can produce aflatoxin B1 (AFB1), which threatens human health. CreA, as the central factor in carbon catabolite repression (CCR), regulates carbon catabolism and AFB1 biosynthesis in A. flavus. Additionally, SsnF-RcoA are recognized as the corepressors of CreA in CCR. In this study, ssnF and rcoA not only regulated the expressions of CCR factors and hydrolase genes, but also positively affected mycelia growth, conidia production, sclerotia formation, and osmotic stress response in A. flavus. More importantly, SsnF and RcoA were identified as positive regulators for AFB1 biosynthesis, as they modulate the AF cluster genes and the relevant regulators at a transcriptional level. Additionally, the interactions of SsnF-CreA and RcoA-CreA were strong and moderate, respectively. However, the interaction of SsnF and RcoA was weak. The interaction models of CreA-SsnF, CreA-RcoA, and SsnF-RcoA were also simulated with a docking analysis. All things considered, SsnF and RcoA are not just the critical regulators of the CCR pathway, but the global regulators involving in morphological development and AFB1 biosynthesis in A. flavus.

Peanut Seed Coat Acts as a Physical and Biochemical Barrier against Aspergillus flavus Infection

Aflatoxin contamination is a global menace that adversely affects food crops and human health. Peanut seed coat is the outer layer protecting the cotyledon both at pre- and post-harvest stages from biotic and abiotic stresses. The aim of the present study is to investigate the role of seed coat against A. flavus infection. In-vitro seed colonization (IVSC) with and without seed coat showed that the seed coat acts as a physical barrier, and the developmental series of peanut seed coat showed the formation of a robust multilayered protective seed coat. Radial growth bioassay revealed that both insoluble and soluble seed coat extracts from 55-437 line (resistant) showed higher A. flavus inhibition compared to TMV-2 line (susceptible). Further analysis of seed coat biochemicals showed that hydroxycinnamic and hydroxybenzoic acid derivatives are the predominant phenolic compounds, and addition of these compounds to the media inhibited A. flavus growth. Gene expression analysis showed that genes involved in lignin monomer, proanthocyanidin, and flavonoid biosynthesis are highly abundant in 55-437 compared to TMV-2 seed coats. Overall, the present study showed that the seed coat acts as a physical and biochemical barrier against A. flavus infection and its potential use in mitigating the aflatoxin contamination.

Eurotium Cristatum Postfermentation of Fireweed and Apple Tree Leaf Herbal Teas

Fungi Eurotium spp. are the main biological agents that ferment the leaves of the Camellia sinensis tea bush to form a popular food product, postfermented tea. The fungus E. cristatum, stored in the collection of the Gause Institute of New Antibiotics under the number INA 01267, was isolated and identified from a briquette of Fujian Chinese tea. The species identification was carried out based on morphocultural characteristics and DNA sequencing. This study is aimed at determining the feasibility of making postfermented herbal teas using E. cristatum and to evaluate their quality. Autofermented herbal teas from Chamaenerion angustifolium (fireweed) and Malus domestica (apple tree) served as the starting material for this study. The change in the concentration of phenolic compounds, organic acids, sugars, and free amino acids was observed for herbal teas subjected to postfermentation with E. cristatum INA 01267. It was found that the E. cristatum INA 01267 strain does not have antimicrobial activity and does not form mycotoxins, which is an indicator of food safety.

Current Practices for Reference Gene Selection in RT-qPCR of Aspergillus: Outlook and Recommendations for the Future

Aspergillus is a genus of filamentous fungi with vast geographic and ecological distributions. Species within this genus are clinically, agriculturally and biotechnologically relevant, leading to increasing interest in elucidating gene expression dynamics of key metabolic and physiological processes. Reverse-transcription quantitative Polymerase Chain Reaction (RT-qPCR) is a sensitive and specific method of quantifying gene expression. A crucial step for comparing RT-qPCR results between strains and experimental conditions is normalisation to experimentally validated reference gene(s). In this review, we provide a critical analysis of current reference gene selection and validation practices for RT-qPCR gene expression analyses of Aspergillus. Of 90 primary research articles obtained through our PubMed query, 17 experimentally validated the reference gene(s) used. Twenty reference genes were used across the 90 studies, with beta-tubulin being the most used reference gene, followed by actin, 18S rRNA and glyceraldehyde 3-phosphate dehydrogenase. Sixteen of the 90 studies used multiple reference genes for normalisation. Failing to experimentally validate the stability of reference genes can lead to conflicting results, as was the case for four studies. Overall, our review highlights the need to experimentally validate reference genes in RT-qPCR studies of Aspergillus.

Rhamnolipids inhibit aflatoxins production in Aspergillus flavus by causing structural damages in the fungal hyphae and down-regulating the expression of their biosynthetic genes

Aflatoxins are hepatotoxic and carcinogenic fungal secondary metabolites that usually contaminate crops and represent a serious health hazard for humans and animals worldwide. In this work, the effect of rhamnolipids (RLs) produced by Pseudomonas aeruginosa #112 on the growth and aflatoxins production by Aspergillus flavus MUM 17.14 was studied in vitro. At concentrations between 45 and 1500 mg/L, RLs reduced the mycelial growth of A. flavus by 23-40% and the production of aflatoxins by 93.9-99.5%. Purified mono-RLs and di-RLs exhibited a similar inhibitory activity on fungal growth. However, the RL mixture had a stronger inhibitory effect on aflatoxins production at concentrations up to 190 mg/L, probably due to a synergistic effect resulting from the combination of both congeners. Using transmission electron microscopy, it was demonstrated that RLs damaged the cell wall and the cytoplasmic membrane of the fungus, leading to the loss of intracellular content. This disruptive phenomenon explains the growth inhibition observed. Furthermore, RLs down-regulated the expression of genes aflC, aflE, aflP and aflQ involved in the aflatoxins biosynthetic pathway (6.4, 44.3, 38.1 and 2.0-fold, respectively), which is in agreement with the almost complete inhibition of aflatoxins production. Overall, the results herein gathered demonstrate for the first time that RLs could be used against aflatoxigenic fungi to attenuate the production of aflatoxins, and unraveled some of their mechanisms of action.