Isolation and identification of a Bacillus megaterium strain with ochratoxin A removal ability and antifungal activity

Analysis of fungal diversity in processed jujube products and the production of mycotoxins by typical toxigenic Aspergillus spp

Processed jujube products are susceptible to contamination by fungi such as Aspergillus spp., which produces mycotoxins that could lead to health problems in consumers. In this study, 58 samples of processed jujube products (including 5 types such as dried jujubes) were collected from different markets in Shihezi (Xinjiang, China). The fungal diversity and the fungi isolated from processed jujube products were systematically analyzed through high-throughput sequencing and molecular biological identification (based on the ITS and/or BenA and CaM regions). In total, the 105 strains of fungi were isolated and identified as belonging to the dominant genera were Aspergillus, Cladosporium, Alternaria, and Penicillium. High-throughput sequencing indicated that Alternaria, Didymella, Cladosporium, and Aspergillus were the dominant fungi in processed jujube products. ELISA showed that A. flavus produced about 19.3862-21.7583 μg/L, 6.5309-11.0411 μg/L, 0-15.4407 μg/L, 0-5.6354 μg/L, and 0-6.0545 μg/L of AFT, AFB1, AFB2, AFM1, and AFM2, respectively. In addition, concentrations of OTA produced by A. niger, A. tubingensis, and A. ochraceus were found to range from 5.2019 to 18.5207 μg/L. Therefore, the separation of Aspergillus with good mycotoxin-producing abilities from processed jujube products poses a latent threat to consumer health.

Reduction in Ochratoxin A Occurrence in Coffee: From Good Practices to Biocontrol Agents

Ochratoxin A (OTA) is a mycotoxin mainly produced by Aspergillus section Circumdati and section Nigri across the coffee chain. OTA is nephrotoxic and is a threat to human health. This review summarizes current knowledge on how to reduce OTA concentration in coffee from farm to cup. After a brief introduction to the OTA occurrence in coffee, current good management practices are introduced. The core of this review focuses on biocontrol and microbial decontamination by lactic acid bacteria, yeasts and fungi, and their associated enzymes currently reported in the literature. Special attention is given to publications closest to in vivo applications of biocontrol agents and microbial OTA adsorption or degradation agents. Finally, this review provides an opinion on which future techniques to promote within the coffee supply chain.

Two different types of hydrolases co-degrade ochratoxin A in a highly efficient degradation strain Lysobacter sp. CW239

Ochratoxin A (OTA) is a toxic secondary metabolite that widely contaminates agro-products and poses a significant dietary risk to human health. Previously, a carboxypeptidase CP4 was characterized for OTA degradation in Lysobacter sp. CW239, but the degradation activity was much lower than its host strain CW239. In this study, an amidohydrolase ADH2 was screened for OTA hydrolysis in this strain. The result showed that 50 μg/L OTA was completely degraded by 1.0 μg/mL rADH2 within 5 min, indicating ultra-efficient activity. Meanwhile, the two hydrolases (i.e., CP4 and ADH2) in the strain CW239 showed the same degradation manner, which transformed the OTA to ochratoxin α (OTα) and l-β-phenylalanine. Gene mutants (Δcp4, Δadh2 and Δcp4-adh2) testing result showed that OTA was co-degraded by carboxypeptidase CP4 and amidohydrolase ADH2, and the two hydrolases are sole agents in strain CW239 for OTA degradation. Hereinto, the ADH2 was the overwhelming efficient hydrolase, and the two types of hydrolases co-degraded OTA in CW239 by synergistic effect. The results of this study are highly significant to ochratoxin A contamination control during agro-products production and postharvest.

Volatile Organic Compounds of Wickerhamomyces anomalus Prevent Postharvest Black Spot Disease in Tomato

Postharvest diseases, such as black spots caused by Alternaria alternata, have caused huge economic losses to the tomato industry and seriously restricted its development. In recent years, biological control has become a new method to control postharvest diseases of fruits and vegetables. Our research group screened W. anomalus, a yeast demonstrating a promising control effect on a postharvest black spot disease of tomatoes, and explored its physiological mechanism of prevention and control. Therefore, this study investigated the prevention and control effect of metabolites of W. anomalus on tomato black spot disease and the inhibition effect of main components on A. alternata. A GC-MS analysis found that isoamyl acetate was the main component of W. anomalus that played an inhibitory role. The results showed that isoamyl acetate could inhibit the growth of A. alternata and had a certain control effect on postharvest black spots in tomatoes. Our findings suggest that isoamyl acetate could be a promising alternative to fungicides for controlling postharvest black spots in tomatoes.

Comprehensive Insights into Ochratoxin A: Occurrence, Analysis, and Control Strategies

Ochratoxin A (OTA) is a toxic mycotoxin produced by some mold species from genera Penicillium and Aspergillus. OTA has been detected in cereals, cereal-derived products, dried fruits, wine, grape juice, beer, tea, coffee, cocoa, nuts, spices, licorice, processed meat, cheese, and other foods. OTA can induce a wide range of health effects attributable to its toxicological properties, including teratogenicity, immunotoxicity, carcinogenicity, genotoxicity, neurotoxicity, and hepatotoxicity. OTA is not only toxic to humans but also harmful to livestock like cows, goats, and poultry. This is why the European Union and various countries regulate the maximum permitted levels of OTA in foods. This review intends to summarize all the main aspects concerning OTA, starting from the chemical structure and fungi that produce it, its presence in food, its toxicity, and methods of analysis, as well as control strategies, including both fungal development and methods of inactivation of the molecule. Finally, the review provides some ideas for future approaches aimed at reducing the OTA levels in foods.

Crude Lipopeptides Produced by Bacillus amyloliquefaciens Could Control the Growth of Alternaria alternata and Production of Alternaria Toxins in Processing Tomato

Alternaria spp. and its toxins are the main contaminants in processing tomato. Based on our earlier research, the current study looked into the anti-fungal capacity of crude lipopeptides from B. amyloliquefaciens XJ-BV2007 against A. alternata. We found that the crude lipopeptides significantly inhibited A. alternata growth and reduced tomato black spot disease incidence. SEM analysis found that the crude lipopeptides could change the morphology of mycelium and spores of A. alternata. Four main Alternaria toxins were detected using UPLC-MS/MS, and the findings demonstrated that the crude lipopeptides could lessen the accumulation of Alternaria toxins in vivo and in vitro. Meanwhile, under the stress of crude lipopeptides, the expression of critical biosynthetic genes responsible for TeA, AOH, and AME was substantially down-regulated. The inhibitory mechanism of the crude lipopeptides was demonstrated to be the disruption of the mycelial structure of A. alternata, as well as the integrity and permeability of the membrane of A. alternata sporocytes. Taken together, crude lipopeptides extracted from B. amyloliquefaciens XJ-BV2007 are an effective biological agent for controlling tomato black spot disease and Alternaria toxins contamination.

Approach for quick exploration of highly effective broad-spectrum biocontrol strains based on PO8 protein inhibition

Aflatoxin is a group of strongly toxic and carcinogenic mycotoxins produced by Aspergillus flavus and other Aspergillus species, which caused food contamination and food loss problems widely across the world especially in developing countries, thus threatening human health and sustainable development. So, it is important to develop new, green, and broad-spectrum biocontrol technology for the prevention of aflatoxin contamination sources. Previously, we found that the PO8 protein from aflatoxigenic A. flavus could be used as a biomarker to predict aflatoxin production in peanuts (so the PO8 is named as an early warning molecule), which infers that the PO8 is relative to aflatoxin production. Therefore, in the study, based on inhibiting the PO8, a new and quick strategy for screening aflatoxin biocontrol strains for developing control agents was presented. With the PO8 inhibition method, four biocontrol strains (2 strains were isolated from peanut kernels with sterilized surface and another 2 strains from peanut rhizosphere soil) were selected and combined to increase prevention wide-spectrum. As a result, the combination showed over 90% inhibition to all tested aflatoxigenic A. flavus isolated from three different peanut production areas (north, middle, and south areas of China), and better than any single strain. The field experiments located in five provinces of China showed that the practice prevention effects (inhibition of aflatoxigenic fungi on the surface of the peanuts) were from 50% to over 80%. The results indicated that the strategy of inhibiting the early warning molecule PO8 can be used to develop aflatoxin control agents well.

Preparation of a new biochar-based microbial fertilizer: Nutrient release patterns and synergistic mechanisms to improve soil fertility

The contradiction between population growth and soil degradation has been increasingly prominent, such that novel fertilizers (e.g., biochar and microbial fertilizers) should be urgently developed. Biochar is a promising fertilizer carrier for microbial fertilizers due to its porous structure. However, the preparation and mechanisms of the effects of biochar-based microbial fertilizers have been rarely investigated. In this study, biochar, Bacillus, and exogenous N-P-K fertilizers served as the raw materials to prepare biochar-based microbial fertilizers (BCMFs) by optimizing the preparation methods and the process parameters. Moreover, the release patterns of N-P-K were analyzed. A pot experiment was performed on pakchoi to examine the effect of the BCMFs and explore its synergistic effect on soil fertility. The results of this study indicated that adsorption by biochar maintained bacterial activity, whereas the granulation process reduced bacterial activity. The adsorption-granulation process increased the content of total nitrogen and organic matter in the soil while enhancing the slow-release effect of the BCMFs. The Elovich model was capable of describing the nitrogen release of the BCMFs, including the diffusion and chemical processes. As indicated by the result of the column leaching experiment, the BCMFs stopped nutrient leaching more significantly than the conventional fertilizers (CF), especially in stopping N and P leaching. The use of the BCMFs improved the available soil nutrients and soil quality while enhancing the abundance of bacteria correlated with carbon and nitrogen metabolism in the soil. Moreover, a 20 % reduction in the use of the BCMFs did not significantly affect the soil available N and P and the growth status of pakchoi. The result of redundancy analysis indicated that the cation exchange capacity (CEC), NH₄⁺-N, NO₃^--N, β-glucosidase (BG), urease (URE), and alkaline phosphatase (AlkP) were the six critical environmental factors for the microbial community structure and could explain 94.8 % of the variance. The BCMFs up-regulated the levels of the above six factors, especially CEC and BG, thus improving the soil quality and enhancing the soil fertility.

Effects of Bacillus amyloliquefaciens XJ-BV2007 on Growth of Alternaria alternata and Production of Tenuazonic Acid

Large amounts of processing tomato are grown in Xinjiang, China. Tomato black spot disease, caused by Alternaria spp., and the produced alternaria toxins in tomato products are posing risks to human health. In this study, we isolated a rhizospheric bacterium, XJ-BV2007, from tomato (Solanum lycopersicum) fields, which we identified as Bacillus amyloliquefaciens. We found that this bacterium has a strong antagonistic effect against Alternaria alternata and reduces the accumulation of alternaria toxins in tomatoes. According to the antifungal activity of the bacteria-free filtrate, we revealed that B. amyloliquefaciens XJ-BV2007 suppresses A. alternata by the production of antifungal metabolites. Combining semi-preparative high-performance liquid chromatography, we employed UPLC-QTOF-MS analysis and the Oxford cup experiment to find that fengycin plays an important role in inhibiting A. alternata. This paper firstly reported that B. amyloliquefaciens efficiently controls tomato black spot disease and mycotoxins caused by A. alternata. B. amyloliquefaciens XJ-BV2007 may provide an alternative biocontrol strain for the prevention of tomato black spot disease.

Unveiling ochratoxin a controlling and biodetoxification molecular mechanisms: Opportunities to secure foodstuffs from OTA contamination

Anarchic growth of ochratoxin A (OTA) producing fungi during crop production, prolonged storage, and processing results in OTA contamination in foodstuffs. OTA in food exacerbates the risk of health and economic problems for consumers and farmers worldwide. Although the toxic effects of OTA on human health have not been well established, comprehensive preventive and remedial measures will be essential to eliminate OTA from foodstuffs. Strict regulations, controlling OTA at pre- or post-harvest stage, and decontamination of OTA have been adopted to prevent human and animal OTA exposure. Biological control of OTA and bio-decontamination are the most promising strategies due to their safety, specificity and nutritional value. This review addresses the current understanding of OTA biodegradation mechanisms and recent developments in OTA control and bio-decontamination strategies. Additionally, this review analyses the strength and weaknesses of different OTA control methods and the contemporary approaches to enhance the efficiency of biocontrol agents. Overall, this review will support the implementation of new strategies to effectively control OTA in food sectors. Further studies on efficacy-related issues, production issues and cost-effectiveness of OTA biocontrol are to be carried out to improve the knowledge, develop improved delivery technologies and safeguard the durability of OTA biocontrol approaches.

Characterization of Bacillus velezensis E2 with abilities to degrade ochratoxin A and biocontrol against Aspergillus westerdijkiae fc-1

Ochratoxin A (OTA), primarily produced by the fungi belonging to the species of Aspergillus and Penicillium, is one of the most common mycotoxins found in cereals and fruits. In addition to resulting in huge economic losses, OTA contamination also poses considerable threat to human and livestock health. Microbial degradation of mycotoxins has been considered with great potential in mycotoxins decontamination. In a previous study, Bacillus velezensis E2 was isolated by our laboratory and showed appreciable inhibitory effect on Aspergillus flavus growth and aflatoxin production in rice grains. In this study, B. velezensis E2 was investigated for its ability to remove OTA and biocontrol against the ochratoxigenic Aspergillus westerdijkiae fc-1. The results revealed that B. velezensis E2 has considerable inhibitory effect on A. westerdijkiae fc-1 both on PDA medium and pear fruits, with inhibitory rate of 51.7% and 73.9%, respectively. In addition, its ability to remove OTA was evaluated in liquid medium and the results showed that more than 96.1% of OTA with an initial concentration of 2.5 μg/mL could be removed by B. velezensis E2 in 48 h. Further experiments revealed that enzymatic transformation and alkaline hydrolysis might be the main mechanisms related to OTA degradation by B. velezensis E2, with ring open ochratoxin α (OP-OTα) as a possible degradation product. Our study indicated that the B. velezensis E2 strain could be a potential bacterial candidate in biodegradation of OTA and biocontrol against A. westerdijkiae fc-1.

Ochratoxin A: Occurrence and recent advances in detoxification

Ochratoxin A (OTA), one of the most important mycotoxins, is mainly produced by fungi in the genera Aspergillus and Penicillium, and commonly found in food and agricultural products. In addition to causing significant economic losses, the occurrence of OTA in foods poses a serious threat to human health. Therefore, it is very important to develop approaches to control or detoxify OTA contamination and thus ensure food safety. In this paper, we review the source and occurrence of OTA in food and agricultural products and the latest achievements in the removal and detoxification of OTA using physical, chemical, and biological methods, with specific attention to influencing factors and mechanisms related to the biodetoxification of OTA. Moreover, the advantages and disadvantages of these methods and their potential application prospect were also discussed.

Screening of Bacillus velezensis E2 and the Inhibitory Effect of Its Antifungal Substances on Aspergillus flavus

Aspergilus flavus is the main pathogenic fungus that causes food mold. Effective control of A. flavus contamination is essential to ensure food safety. The lipopeptides (LPs) produced by Bacillus strains have been shown to have an obvious antifungal effect on molds. In this study, an antagonist strain of Bacillus velezensis with obvious antifungal activity against A. flavus was isolated from the surface of healthy rice. Using HPLC-MS analysis, the main components of LPs produced by strain E2 were identified as fengycin and iturins. Further investigations showed that LPs could inhibit the spore germination, and even cause abnormal expansion of hyphae and cell rupture. Transcriptomic analyses showed that some genes, involved in ribosome biogenesis in eukaryotes (NOG1, KRE33) and aflatoxin biosynthesis (aflK, aflR, veA, omtA) pathways in A. flavus were significantly down-regulated by LPs. In conclusion, this study provides novel insights into the cellular and molecular antifungal mechanisms of LPs against grain A. flavus contamination.

A DNA tetrahedral nanomaterial-based dual-signal ratiometric electrochemical aptasensor for the detection of ochratoxin A in corn kernel samples

Ochratoxin A (OTA) is a highly toxic food contaminant and is harmful to human beings.

Microbiological Decontamination of Mycotoxins: Opportunities and Limitations

The contamination of food and feeds with mycotoxins poses a global health risk to humans and animals, with major economic consequences. Good agricultural and manufacturing practices can help control mycotoxin contamination. Since these actions are not always effective, several methods of decontamination have also been developed, including physical, chemical, and biological methods. Biological decontamination using microorganisms has revealed new opportunities. However, these biological methods require legal regulations and more research before they can be used in food production. Currently, only selected biological methods are acceptable for the decontamination of feed. This review discusses the literature on the use of microorganisms to remove mycotoxins and presents their possible mechanisms of action. Special attention is given to Saccharomyces cerevisiae yeast and lactic acid bacteria, and the use of yeast cell wall derivatives.

Antagonistic Effects of Delia antiqua (Diptera: Anthomyiidae)-Associated Bacteria Against Four Phytopathogens

Recent studies have revealed multiple roles of insect-associated microbes such as lignin degradation, entomopathogen inhibition, and antibiotic production. These functions improve insect host fitness, and provide a novel source of discovering beneficial microbes for industrial and agricultural production. Previously published research found that in the symbiosis formed by the dipteran pest Delia antiqua (Meigen) (Diptera: Anthomyiidae) and its associated bacteria, the bacteria showed effective inhibition of one fungal entomopathogen, Beauveria bassiana. The antifungal activity of those associated bacteria indicates their potential to be used as biocontrol agents for fungal phytopathogens. In this study, we first isolated and identified bacteria associated with D. antiqua using a culture-dependent method. Second, we tested the antifungal activity of these bacteria against four phytopathogens including Fusarium moniliforme, Botryosphaeria dothidea, and two Fusarium oxysporum strains using the dual-culture method. In total, 74 species belonging to 30 genera, 23 families, eight classes, and four phyla were isolated and identified. Among those bacteria, Ochrobactrum anthropi, Morganella morganii, Arthrobacter sp. 3, and Acinetobacter guillouiae showed significant volatile inhibition activity against F. moniliforme, B. dothidea, and both F. oxysporum, respectively. Moreover, bacteria including Rhodococcus equi, Leucobacter aridicollis, Paenibacillus sp. 3, and Lampropedia sp. showed significant contact inhibition activity against F. moniliforme, B. dothidea, and both F. oxysporum. Our work provides a new source for discovering biocontrol agents against phytopathogens.

Isolation and characterization of a Pseudomonas poae JSU-Y1 with patulin degradation ability and biocontrol potential against Penicillium expansum

Patulin, one of the most common mycotoxins produced primarily by the Penicillium, Aspergillus and Byssochlamys species, is often associated with fruits and fruit-based products. Biodegradation by microbes is an effective method to remove or detoxify mycotoxins. In this study, a bacterial strain with patulin degradation capability was selectively isolated using oxindole, an analogue to patulin, as the sole carbon source, and identified as Pseudomonas poae JSU-Y1 by phylogenetic analysis on the basis of 16S rRNA sequence. This isolated bacterium could inhibit the growth of Penicillium expansum both on plate medium and apple fruit with inhibition ratio of 30.3% and 44.9%, respectively. Up to 87.7% of the initial patulin (2.5 μg/mL) was removed after incubation with Pseudomonas poae JSU-Y1 in liquid medium at 30 °C for 72 h. When challenged with apple juice, 79% of patulin could be degraded by this isolated strain. Additionally, ascladiol was tentatively identified as the patulin degradation intermediate by LC-MS analysis. Taken together, the experiment results indicated that the isolated Pseudomonas poae JSU-Y1 would be a promising bacterial resource to control patulin contamination and toxigenic fungal growth in agricultural products.

Antifungal activity of chitosan against Aspergillus ochraceus and its possible mechanisms of action

Chitosan is a polysaccharide with a wide-range antimicrobial spectrum and has been shown to be effective in control postharvest diseases of various fruit, but the possible mode of action is far from well known. In this study the antifungal activity of chitosan was tested on A. ochraceus and its possible mechanisms involved were also investigated both at microstructure and transcriptome level. Here, we found that chitosan could significantly inhibited spore germination and mycelia growth of A. ochraceus. Scan electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that chitosan induced remarkable changes in morphology and microstructure of hyphae, such as shriveling, abnormal branching and vacuolation. Changes in expression profiles of A. ochraceus upon chitosan treatment were analyzed by RNA sequencing and a total of 435 differentially expressed genes (DEGs) were identified. Further KEGG analysis revealed that DEGs involved in ribosome biogenesis were down-regulated, while DEGs related to membrane homeostasis, such as glycerophospholipid metabolism, ether lipid metabolism and steroid biosynthesis, were up-regulated. Chitosan may affect the growth and development of A. ochraceus by impairing the integrity of cell surface architecture and protein biosynthesis. These findings have practical implications with respect to the use of chitosan as an alternative way for controlling fungal pathogens.