Inhibition of Aflatoxin Production by Paraquat and External Superoxide Dismutase in Aspergillus flavus

Mechanism of inactivation of Aspergillus flavus spores by dielectric barrier discharge plasma

Dielectric barrier discharge plasma (DBDP) displays strong against fungal spores, while its precise mechanism of spore inactivation remains inadequately understood. In this study, we applied morphological, in vivo and in vitro experiments, transcriptomics, and physicochemical detection to unveil the potential molecular pathways underlying the inactivation of Aspergillus flavus spores by DBDP. Our findings suggested that mycelium growth was inhibited as observed by SEM after 30 s treatment at 70 kV, meanwhile spore germination ceased and clustering occurred. It led to the release of cellular contents and subsequent spore demise by disrupting the integrity of spore membrane. Additionally, based on the transcriptomic data, we hypothesized that the induction of spore inactivation by DBDP might be associated with downregulation of genes related to cell membranes, organelles (mitochondria), oxidative phosphorylation, and the tricarboxylic acid cycle. Subsequently, we validated our transcriptomic findings by measuring the levels of relevant enzymes in metabolic pathways, such as superoxide dismutase, acetyl-CoA, total dehydrogenase, and ATP. These physicochemical indicators revealed that DBDP treatment resulted in mitochondrial dysfunction, redox imbalance, and inhibited energy metabolism pathways. These findings were consistent with the transcriptomic results. Hence, we concluded that DBDP accelerated spore rupture and death via ROS-mediated mitochondrial dysfunction, which does not depend on cell membranes.

Prediction and validation of enzymatic degradation of aflatoxin M1: Genomics and proteomics analysis of Bacillus pumilus E-1-1-1 enzymes

Aflatoxins are a class of highly toxic mycotoxins. Aflatoxin M1 (AFM1) is hydroxylated metabolite of aflatoxin B1, having comparable toxicity, which is more commonly found in milk. In this study, the whole genome sequencing of Bacillus pumilus E-1-1-1 isolated from feces of 38 kinds of animals, having aflatoxin M1 degradation ability was conducted. Bacterial genome sequencing indicated that a total of 3445 sequences were finally annotated on 23 different cluster of orthologous groups (COG) categories. Then, the potential AFM1 degradation proteins were verified by proteomics; the properties of these proteins were further explored, including protein molecular weight, hydrophobicity, secondary structure prediction, and three-dimensional structures. Bacterial genome sequencing combined with proteomics showed that eight genes were the most capable of degrading AFM1 including three catalases, one superoxide dismutase, and four peroxidases to clone. These eight genes with AFM1 degrading capacity were successfully expressed. These results indicated that AFM1 can be degraded by Bacillus pumilus E-1-1-1 protein and the most degrading proteins were oxidoreductases.

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.

Advanced mycotoxin control and decontamination techniques in view of an increased aflatoxin risk in Europe due to climate change

Aflatoxins are toxic secondary metabolites produced by Aspergillus spp. found in staple food and feed commodities worldwide. Aflatoxins are carcinogenic, teratogenic, and mutagenic, and pose a serious threat to the health of both humans and animals. The global economy and trade are significantly affected as well. Various models and datasets related to aflatoxins in maize have been developed and used but have not yet been linked. The prevention of crop loss due to aflatoxin contamination is complex and challenging. Hence, the set-up of advanced decontamination is crucial to cope with the challenge of climate change, growing population, unstable political scenarios, and food security problems also in European countries. After harvest, decontamination methods can be applied during transport, storage, or processing, but their application for aflatoxin reduction is still limited. Therefore, this review aims to investigate the effects of environmental factors on aflatoxin production because of climate change and to critically discuss the present-day and novel decontamination techniques to unravel gaps and limitations to propose them as a tool to tackle an increased aflatoxin risk in Europe.

Superoxide Dismutases in Eukaryotic Microorganisms: Four Case Studies

Various components in the cell are responsible for maintaining physiological levels of reactive oxygen species (ROS). Several different enzymes exist that can convert or degrade ROS; among them are the superoxide dismutases (SODs). If left unchecked, ROS can cause damage that leads to pathology, can contribute to aging, and may, ultimately, cause death. SODs are responsible for converting superoxide anions to hydrogen peroxide by dismutation. Here we review the role of different SODs on the development and pathogenicity of various eukaryotic microorganisms relevant to human health. These include the fungal aging model, Podospora anserina; various members of the genus Aspergillus that can potentially cause aspergillosis; the agents of diseases such as Chagas and sleeping disease, Trypanosoma cruzi and Trypanosoma brucei, respectively; and, finally, pathogenic amoebae, such as Acanthamoeba spp. In these organisms, SODs fulfill essential and often regulatory functions that come into play during processes such as the development, host infection, propagation, and control of gene expression. We explore the contribution of SODs and their related factors in these microorganisms, which have an established role in health and disease.

Influence of H2O2-Induced Oxidative Stress on In Vitro Growth and Moniliformin and Fumonisins Accumulation by Fusarium proliferatum and Fusarium subglutinans

Fusarium proliferatum and Fusarium subglutinans are common pathogens of maize which are known to produce mycotoxins, including moniliformin (MON) and fumonisins (FBs). Fungal secondary metabolism and response to oxidative stress are interlaced, where hydrogen peroxide (H₂O₂) plays a pivotal role in the modulation of mycotoxin production. The objective of this study is to examine the effect of H₂O₂-induced oxidative stress on fungal growth, as well as MON and FBs production, in different isolates of these fungi. When these isolates were cultured in the presence of 1, 2, 5, and 10 mM H₂O₂, the fungal biomass of F. subglutinans isolates showed a strong sensitivity to increasing oxidative conditions (27–58% reduction), whereas F. proliferatum isolates were not affected or even slightly improved (45% increase). H₂O₂ treatment at the lower concentration of 1 mM caused an almost total disappearance of MON and a strong reduction of FBs content in the two fungal species and isolates tested. The catalase activity, surveyed due to its crucial role as an H₂O₂ scavenger, showed no significant changes at 1 mM H₂O₂ treatment, thus indicating a lack of correlation with MON and FB changes. H₂O₂ treatment was also able to reduce MON and FB content in certified maize material, and the same behavior was observed in the presence and absence of these fungi, highlighting a direct effect of H₂O₂ on the stability of these mycotoxins. Taken together, these data provide insights into the role of H₂O₂ which, when increased under stress conditions, could affect the vegetative response and mycotoxin production (and degradation) of these fungi.

In vitro activity of encapsulated lactic acid bacteria on aflatoxin production and growth of Aspergillus Spp

This study aimed to investigate the potential ability of simultaneously used L. acidophilus(LA-5), L.rhamnosus(LGG), and L.casei(LC-01) in encapsulated (E) and nonencapsulated (NE) forms in mycelial growth of Aspergillus spp and aflatoxin production by A. flavus. In order to assess the zone of fungal growth inhibition by E and NE lactic acid bacteria, the agar well diffusion method was applied. Quantification of aflatoxin was performed using a high-performance liquid chromatography technique. Lactic acid bacteria exhibited high antifungal activity and significantly reduced AFB1, AFB2, AFG1, and AFG2 production in both E and NE forms compared to the control group. The percentage of reduction in total AFs production in treated samples with E and NE lactic acid bacteria was 94.1% and 95.5%, respectively. These results suggested that simultaneously used lactic acid bacteria in E and NE forms can prevent growth and decrease aflatoxin production of toxigenic aspergilla.

Inhibition analysis of aflatoxin by in silico targeting the thioesterase domain of polyketide synthase enzyme in Aspergillus ssp

The spread of fungal growth causes enormous economic, agricultural, and health problems for humans, such as Aspergillus sp., which produce aflatoxins. Thus, the inhibition of aflatoxin production became a precious target. In this research, the thioesterase (TE) domain from Polyketide synthase enzyme was selected to employ the in silico docking, using AutoDock Vina, against 623 natural compounds from the South African natural compound database (SANCDB), to identify potential inhibitors that can selectively inhibit thioesterase domain. The top ten inhibitors components were pinocembrin, typhaphthalide, p-coumaroylputrescine, dilemmaone A, 9-angelylplatynecine, 2,4,6-octatrienal, 4,8-dichloro-3,7-dimethyl-, (2e,4z,6e)-, lilacinobiose, 1,3,7-octatriene, 5,6-dichloro-2-(dichloromethyl)-6-methyl-, [r*,s*-(e)]-(-)- (9ci), lilacinobiose, 1,3,7-octatriene, 5,6-dichloro-2-(dichloromethyl)-6-methyl-, [r*,s*-(e)]-(-)- (9ci), 1,3,7-octatriene, 1,5,6-trichloro-2-(dichloromethyl)-6-methyl-, [r*,s*-(z,e)] and 9-angelylhastanecine and that depending on the lowest binding energy, the best chemical interactions and the best drug-likeness. The results of those components gave successful inhibition with the thioesterase domain. So, they can be used for inhibition and controlling aflatoxin contamination of agriculture crop yields, specially, pinocembrin which gave promising results.Communicated by Ramaswamy H. Sarma.

FvmnSOD is involved in oxidative stress defence, mitochondrial stability and apoptosis prevention in Fusarium verticillioides

Superoxide dismutases are key enzymes in elimination of the superoxide anion radical (O₂ ^•- ) generated intracellularly or by exogenous oxidative stress eliciting agents, like menadione. In this study, we investigated the physiological role of the manganese superoxide dismutase-encoding gene in Fusarium verticillioides via the construction of a gene deletion mutant, ΔFvmnSOD and comparing its phenotype with that of the wild-type parental strain and a ΔFvmnSOD' C strain, complemented with the functional manganese superoxide dismutase gene. Deletion of FvmnSOD had no effect on the relative intracellular superoxide ratio but increased the sensitivity of the fungus to menadione sodium bisulphite on Czapek-Dox stress agar plates. The lack of FvmnSOD caused changes in mitochondrial morphology and physiology: The volumetric ratio of these cell organelles in the second hyphal segment, as well as the total, the KCN-sensitive cytochrome c-dependent and the KCN+SHAM (salicylhidroxamic acid)-resistant residual respiration rates, were higher in the mutant as compared to the wild-type and the complemented strains. Nevertheless, changes in the respiration rates were attributable to the higher volumetric ratio of mitochondria found in the gene deletion mutant. Changes in the mitochondrial functions also brought about higher sensitivity to apoptotic cell death elicited by the Penicillium chrysogenum antifungal protein. The gene deletion mutant developed significantly thinner hyphae in comparison to the wild-type strain. Deletion of FvmnSOD had no effect on fumonisin B₁ and B₂ production of the fungus grown in Myro medium as a static culture.

Predominant Mycotoxins, Pathogenesis, Control Measures, and Detection Methods in Fermented Pastes

Fermented pastes are some of the most popular traditional products in China. Many studies reported a strong possibility that fermented pastes promote exposure to mycotoxins, including aflatoxins, ochratoxins, and cereulide, which were proven to be carcinogenic and neurotoxic to humans. The primary mechanism of pathogenicity is by inhibiting protein synthesis and inducing oxidative stress using cytochrome P450 (CYP) enzymes. The level of mycotoxin production is dependent on the pre-harvest or post-harvest stage. It is possible to implement methods to control mycotoxins by using appropriate antagonistic microorganisms, such as Aspergillus niger, Lactobacillus plantarum, and Saccharomyces cerevisiae isolated from ordinary foods. Also, drying products as soon as possible to avoid condensation or moisture absorption in order to reduce the water activity to lower than 0.82 during storage is also effective. Furthermore, organic acid treatment during the soaking process reduces toxins by more than 90%. Some novel detection technologies based on magnetic adsorption, aptamer probes, and molecular-based methods were applied to rapidly and accurately detect mycotoxins in fermented pastes.

Lactic Acid Bacteria as Antifungal and Anti-Mycotoxigenic Agents: A Comprehensive Review

Fungal contamination of food and animal feed, especially by mycotoxigenic fungi, is not only a global food quality concern for food manufacturers, but it also poses serious health concerns because of the production of a variety of mycotoxins, some of which present considerable food safety challenges. In today's mega-scale food and feed productions, which involve a number of processing steps and the use of a variety of ingredients, fungal contamination is regarded as unavoidable, even good manufacturing practices are followed. Chemical preservatives, to some extent, are successful in retarding microbial growth and achieving considerably longer shelf-life. However, the increasing demand for clean label products requires manufacturers to find natural alternatives to replace chemically derived ingredients to guarantee the clean label. Lactic acid bacteria (LAB), with the status generally recognized as safe (GRAS), are apprehended as an apt choice to be used as natural preservatives in food and animal feed to control fungal growth and subsequent mycotoxin production. LAB species produce a vast spectrum of antifungal metabolites to inhibit fungal growth; and also have the capacity to adsorb, degrade, or detoxify fungal mycotoxins including ochratoxins, aflatoxins, and Fusarium toxins. The potential of many LAB species to circumvent spoilage associated with fungi has been exploited in a variety of human food and animal feed stuff. This review provides the most recent updates on the ability of LAB to serve as antifungal and anti-mycotoxigenic agents. In addition, some recent trends of the use of LAB as biopreservative agents against fungal growth and mycotoxin production are highlighted.