The influence of divalent cations and chelators on aflatoxin B1 degradation by Flavobacterium aurantiacum

Co-Cultivation of Two Bacillus Strains for Improved Cell Growth and Enzyme Production to Enhance the Degradation of Aflatoxin B1

Bacillus sp. H16v8 and Bacillus sp. HGD9229 were identified as Aflatoxin B₁ (AFB₁) degrader in nutrient broth after a 12 h incubation at 37 °C. The degradation efficiency of the two-strain supernatant on 100 μg/L AFB₁ was higher than the bacterial cells and cell lysate. Moreover, degradations of AFB₁ were strongly affected by the metal ions in which Cu²⁺ stimulated the degradation and Zn²⁺ inhibited the degradation. The extracellular detoxifying enzymes produced by co-cultivation of two strains were isolated and purified by ultrafiltration. The molecular weight range of the detoxifying enzymes was 20-25 kDa by SDS-PAGE. The co-culture of two strains improved the total cell growth with the enhancement of the total protein content and detoxifying enzyme production. The degradation efficiency of the supernatant from mixed cultures increased by 87.7% and 55.3% compared to Bacillus sp. H16v8 and HGD9229, individually. Moreover, after the degradation of AFB₁, the four products of the lower toxicity were identified by LC-Triple TOF-MS with the two proposed hypothetical degradation pathways.

Control of aflatoxin M1 in milk by novel methods: A review

Aflatoxin M₁ (AFM₁) in milk and milk products has been recognised as an issue for over 30 years. Controlling AFM₁ in milk is important to protect human health and trade. Preventing contamination by avoiding fungal contamination of cattle feed is the best method of control, however this is hard to avoid in some countries. Treating milk containing AFM₁ is an alternative control measure, however, there is no single approved method. The challenge is to select a treatment method that is effective but does not affect the organoleptic quality of milk. This study reviews the strategies for degrading AFM₁ in milk including yeast, lactic acid bacteria, enzyme, peroxide, ozone, UV light and cold plasma. This review compares the efficacy, influencing factors, (possible) mechanisms of activity, advantages, limitations and potential future trends of these methods and provides some recommendations for the treatment of milk to reduce the risk of AFM₁ contamination.

Strategies and Methodologies for Developing Microbial Detoxification Systems to Mitigate Mycotoxins

Mycotoxins, the secondary metabolites of mycotoxigenic fungi, have been found in almost all agricultural commodities worldwide, causing enormous economic losses in livestock production and severe human health problems. Compared to traditional physical adsorption and chemical reactions, interest in biological detoxification methods that are environmentally sound, safe and highly efficient has seen a significant increase in recent years. However, researchers in this field have been facing tremendous unexpected challenges and are eager to find solutions. This review summarizes and assesses the research strategies and methodologies in each phase of the development of microbiological solutions for mycotoxin mitigation. These include screening of functional microbial consortia from natural samples, isolation and identification of single colonies with biotransformation activity, investigation of the physiological characteristics of isolated strains, identification and assessment of the toxicities of biotransformation products, purification of functional enzymes and the application of mycotoxin decontamination to feed/food production. A full understanding and appropriate application of this tool box should be helpful towards the development of novel microbiological solutions on mycotoxin detoxification.

AFM₁ in Milk: Physical, Biological, and Prophylactic Methods to Mitigate Contamination

Aflatoxins (AFs) are toxic, carcinogenic, immunosuppressive secondary metabolites produced by some Aspergillus species which colonize crops, including many dietary staple foods and feed components. AFB₁ is the prevalent and most toxic among AFs. In the liver, it is biotransformed into AFM₁, which is then excreted into the milk of lactating mammals, including dairy animals. AFM₁ has been shown to be cause of both acute and chronic toxicoses. The presence of AFM₁ in milk and dairy products represents a worldwide concern since even small amounts of this metabolite may be of importance as long-term exposure is concerned. Contamination of milk may be mitigated either directly, decreasing the AFM₁ content in contaminated milk, or indirectly, decreasing AFB₁ contamination in the feed of dairy animals. Current strategies for AFM₁ mitigation include good agricultural practices in pre-harvest and post-harvest management of feed crops (including storage) and physical or chemical decontamination of feed and milk. However, no single strategy offers a complete solution to the issue.

Screening a strain of Aspergillus niger and optimization of fermentation conditions for degradation of aflatoxin B₁

Aflatoxin B₁, a type of highly toxic mycotoxin produced by some species belonging to the Aspergillus genus, such as Aspergillus flavus and Aspergillus parasiticus, is widely distributed in feed matrices. Here, coumarin was used as the sole carbon source to screen microorganism strains that were isolated from types of feed ingredients. Only one isolate (ND-1) was able to degrade aflatoxin B₁ after screening. ND-1 isolate, identified as a strain of Aspergillus niger using phylogenetic analysis on the basis of 18S rDNA, could remove 26.3% of aflatoxin B₁ after 48 h of fermentation in nutrient broth (NB). Optimization of fermentation conditions for aflatoxin B₁ degradation by selected Aspergillus niger was also performed. These results showed that 58.2% of aflatoxin B₁ was degraded after 24 h of culture under the optimal fermentation conditions. The aflatoxin B₁ degradation activity of Aspergillus niger supernatant was significantly stronger than cells and cell extracts. Furthermore, effects of temperature, heat treatment, pH, and metal ions on aflatoxin B₁ degradation by the supernatant were examined. Results indicated that aflatoxin B₁ degradation of Aspergillus niger is enzymatic and this process occurs in the extracellular environment.

Adsorption and degradation of zearalenone by bacillus strains

Two Bacillus strains; Bacillus subtilis 168 and Bacillus natto CICC 24640 separately adsorbed and degraded zearalenone in liquid media, in vitro. Viable, autoclaved (121°C, 20 min) and acid-treated cells of both strains separately bound more than 55% of zearalenone (ZEN, 20 μg/L) after 30 min and 1-h incubation at 37°C under aerobic conditions, and the amount of ZEN adsorbed was dependent on initial cell volume. In addition, ZEN was degraded by the culture extract of both strains. Degradation by B. subtilis 168 and B. natto CICC 24640 culture extract after 24-h aerobic incubation at 30°C was 81% and 100%, respectively. B. natto CICC 24640 culture extract comprehensively degraded ZEN and, for both strains, no oestrogenic ZEN analogues were present. ZEN degradation was accompanied by carbondioxide emission indicating a decarboxylation reaction. ZEN degradation by the salient B. natto CICC 24640 culture extract varied with initial ZEN concentration, incubation time, temperature and pH. Degradation was enhanced by Mn(2+), Zn(2+), Ca(2+) and Mg(2+) but impeded by Hg(2+), Cu(2+), Pb(2+), ethylenediaminetetraacetic acid and 1,10-phenanthroline. The degradation reaction is associated with a metalloproteinase of molar mass in the range 31-43 kDa. Overall, the two generally recognised as safe Bacillus strains can, potentially, be utilised for detoxification of zearalenone in food.

Detoxification of aflatoxin B1 by certain bacterial species isolated from Egyptian soil

Aflatoxin contamination of food and grain poses a serious economic and health problem worldwide. Aflatoxin B1 (AFB1) is extremely mutagenic, toxic and a potent carcinogen to both humans and livestock. A safe, effective and environmentally sound detoxification method is needed for controlling this toxin. In this study, 21 soil samples were screened from various sources with vast microbial populations using a coumarin containing medium. Eleven bacterial isolates showing AFB1 reduction activity in a liquid culture medium were selected from the screening experiments. Isolate 12-3 and 12-5, obtained from soil samples of Kafr-Zaiat Pesticide company drainage and identified to be Pseudomonas putida and Escherichia coli, reduced AFB1 by 69.3% and 58.8%, respectively, after incubation in the liquid medium at 37 °C for 72 h. The culture supernatant of these isolates was able to reduce AFB1 effectively by 76.2% and 62.5%, respectively, whereas the viable cells and cell extracts were far less effective. Factors influencing AFB1 detoxification by the culture supernatant were investigated. The highest detoxification activity for P. putida and E. coli was 83.3% and 63.8%, respectively, at pH 8 and 30 °C for 72 h. The detoxification activity was reduced at 10, 20 and 45 °C. The Mg2+, Mn2+, Se and Cu2+ ions were activators for AFB1 detoxification. However, Zn2+ ion was a strong inhibitor. Treatments with proteinase K, proteinase K plus SDS and heating significantly reduced or eradicated the detoxification activity of the culture supernatant. In conclusion, the detoxification of AFB1 by P. putida 12-3 was enzymatic and the enzymes responsible for the detoxification of AFB1 are constitutively extracellular produced. Also, the AFB1 detoxification by E. coli was conducted by enzymes as well as by cell wall binding mechanism. Both bacteria could have great potential in industrial applications.

Microbial strategies to control aflatoxins in food and feed

Aflatoxins are a group of toxic and carcinogenic fungal metabolites. They are commonly found in cereals, nuts and animal feeds and create a significant threat to the food industry and animal production. Several strategies have been developed to avoid or reduce harmful effects of aflatoxins since the 1960s. However, prevention of aflatoxin contamination pre/post harvest or during storage has not been satisfactory and control strategies such as physical removing and chemical inactivating used in food commodities have their deficiencies, which limit their large scale application. It is expected that progress in the control of aflatoxin contamination will depend on the introduction of technologies for specific, efficient and environmentally sound detoxification. The utilisation of biological detoxification agents, such as microorganisms and/or their enzymatic products to detoxify aflatoxins in contaminated food and feed can be a choice of such technology. To date, many of the microbial strategies have only showed reduced concentration of aflatoxins and the structure and toxicity of the detoxified products are unclear. More attention should be paid to the detoxification reactions, the structure of biotransformed products and the enzymes responsible for the detoxification. In this article, microbial strategies for aflatoxin control such as microbial binding and microbial biotransformation are reviewed.

In vitro efficacy of Myxococcus fulvus ANSM068 to biotransform aflatoxin B₁

Aflatoxin B₁ (AFB₁) is commonly found in cereals and animal feeds and causes a significant threat to the food industry and animal production. Several microbial isolates with high AFB₁ transformation ability have been identified in our previous studies. The aim of this research was to characterize one of those isolates, Myxococcus fulvus ANSM068, and to explore its biotransformation mechanism. The bacterial isolate of M. fulvus ANSM068, isolated from deer feces, was able to transform AFB₁ by 80.7% in liquid VY/2 medium after incubation at 30 °C for 72 h. The supernatant of the bacterial culture was more effective in transforming AFB₁ as compared to the cells alone and the cell extract. The transformation activity was significantly reduced and eradicated after the culture supernatant was treated with proteinase K, proteinase K plus SDS and heating. Culture conditions, including nitrogen source, initial pH and incubation temperature were evaluated for an optimal AFB₁ transformation. Liquid chromatography mass spectrometry (LCMS) analyses showed that AFB₁ was transformed to a structurally different compound. Infrared analysis (IR) indicated that the lactone ring on the AFB₁ molecule was modified by the culture supernatant. Chromatographies on DEAE-Ion exchange and Sephadex-Molecular sieve and SDS-PAGE electrophoresis were used to determine active components from the culture supernatant, indicating that enzyme(s) were responsible for the AFB₁ biotransformation. This is the first report on AFB₁ transformation by a strain of myxobacteria through enzymatic reaction(s).

Preparation, purification and characteristics of an aflatoxin degradation enzyme from Myxococcus fulvus ANSM068

AIMS

To prepare, purify and characterize an extracellular enzyme from Myxococcus fulvus ANSM068, designated as myxobacteria aflatoxin degradation enzyme (MADE), which possesses degradation activity against aflatoxin B(1) (AFB(1) ), G(1) (AFG(1) ) and M(1) (AFM(1) ) in solution.

METHODS AND RESULTS

The culture supernatant of strain M. fulvus demonstrated high degradation ability against AFB(1) (71·89%), AFG(1) (68·13%) and AFM(1) (63·82%) after 48 h of incubation. An enzyme was purified from the supernatant of M. fulvus using ethanol precipitation and chromatography on DEAE-Sepharose and Superdex 75. An overall 166-fold purification of the enzyme with a recovery of 57% and a final specific activity of 569·44 × 10(3) U mg(-1) was obtained using the present purification protocol. The apparent molecular mass of MADE was estimated to be 32 kDa by SDS-PAGE. AFG(1) and AFM(1) were significantly degraded, by 96·96 and 95·80%, respectively, when treated with pure MADE (100 U ml(-1) ) produced by strain ANSM068. MADE exhibited the largest amount of activity at 35°C and pH 6·0, with Mg(2+) ions greatly promoting and Zn(2+) strongly inhibiting MADE activity.

CONCLUSIONS

An aflatoxin DEGRADATION ENZYME FROM BACTERIAL ISOLATES CAN EFFECTIVELY REMOVE AFLATOXIN B(1) , G(1) AND M(1) IN SOLUTION.

SIGNIFICANCE AND IMPACT OF THE STUDY

The high activity and wide temperature and pH range of MADE for the degradation of aflatoxin have promising applications in control of mycotoxins during food and feed processing.

Biological strategies to counteract the effects of mycotoxins

Mycotoxins are fungal secondary metabolites that if ingested can cause a variety of adverse effects on both humans and animals, ranging from allergic responses to death. Therefore, exposure to mycotoxins should be minimized. A variety of physical, chemical, and biological methods have been developed for decontamination and/or detoxification of mycotoxins from contaminated foods and feeds. This overview details the latest developments in the biological control of both fungal infection and mycotoxin formation and describes the detoxification of many of the most important mycotoxins by microorganisms. This review also addresses the potential for use of microorganisms as mycotoxin binders in the gastrointestinal tract of both humans and animals, thereby reducing the potential deleterious effects of exposure to these toxins.

Aflatoxin B(1) degradation by Stenotrophomonas maltophilia and other microbes selected using coumarin medium

Aflatoxin B₁ (AFB₁) is one of the most harmful mycotoxins in animal production and food industry. A safe, effective and environmentally sound detoxification method is needed for controlling this toxin. In this study, 65 samples were screened from various sources with vast microbial populations using a newly developed medium containing coumarin as the sole carbon source. Twenty five single-colony bacterial isolates showing AFB₁ reduction activity in a liquid culture medium were selected from the screen. Isolate 35-3, obtained from tapir feces and identified to be Stenotrophomonas maltophilia, reduced AFB₁ by 82.5% after incubation in the liquid medium at 37 °C for 72 h. The culture supernatant of isolate 35-3 was able to degrade AFB₁ effectively, whereas the viable cells and cell extracts were far less effective. Factors influencing AFB₁ degradation by the culture supernatant were investigated. Activity was reduced to 60.8% and 63.5% at 20 °C and 30 °C, respectively, from 78.7% at 37 °C. The highest degradation rate was 84.8% at pH 8 and the lowest was only 14.3% at pH 4.0. Ions Mg²⁺ and Cu²⁺ were activators for AFB₁ degradation, however ion Zn²⁺ was a strong inhibitor. Treatments with proteinase K, proteinase K plus SDS and heating significantly reduced or eradicated the degradation activity of the culture supernatant. The results indicated that the degradation of AFB₁ by S. maltophilia 35-3 was enzymatic and could have a great potential in industrial applications.

Strategies to Prevent Mycotoxin Contamination of Food and Animal Feed: A Review

Mycotoxins are fungal secondary metabolites that have been associated with severe toxic effects to vertebrates produced by many important phytopathogenic and food spoilage fungi including Aspergillus, Penicillium, Fusarium, and Alternaria species. The contamination of foods and animal feeds with mycotoxins is a worldwide problem. We reviewed various control strategies to prevent the growth of mycotoxigenic fungi as well as to inhibit mycotoxin biosynthesis including pre-harvest (resistance varieties, field management and the use of biological and chemical agents), harvest management, and post-harvest (improving of drying and storage conditions, the use of natural and chemical agents, and irradiation) applications. While much work in this area has been performed on the most economically important mycotoxins, aflatoxin B(1) and ochratoxin A much less information is available on other mycotoxins such as trichothecenes, fumonisin B(1), zearalenone, citrinin, and patulin. In addition, physical, chemical, and biological detoxification methods used to prevent exposure to the toxic and carcinogenic effect of mycotoxins are discussed. Finally, dietary strategies, which are one of the most recent approaches to counteract the mycotoxin problem with special emphasis on in vivo and in vitro efficacy of several of binding agents (activated carbons, hydrated sodium calcium aluminosilicate, bentonite, zeolites, and lactic acid bacteria) have also been reviewed.