Mathematic modeling for optimum conditions on aflatoxin B₁degradation by the aerobic bacterium Rhodococcus erythropolis

Optimization of Rhodococcus erythropolis JCM3201T Nutrient Media to Improve Biomass, Lipid, and Carotenoid Yield Using Response Surface Methodology

The oleaginous bacterium Rhodococcus erythropolis JCM3201T offers various unique enzyme capabilities, and it is a potential producer of industrially relevant compounds, such as triacylglycerol and carotenoids. To develop this strain into an efficient production platform, the characterization of the strain's nutritional requirement is necessary. In this work, we investigate its substrate adaptability. Therefore, the strain was cultivated using nine nitrogen and eight carbon sources at a carbon (16 g L-1) and nitrogen (0.16 g L-1) weight ratio of 100:1. The highest biomass accumulation (3.1 ± 0.14 g L-1) was achieved using glucose and ammonium acetate. The highest lipid yield (156.7 ± 23.0 mg g-1DCW) was achieved using glucose and yeast extract after 192 h. In order to enhance the dependent variables: biomass, lipid and carotenoid accumulation after 192 h, for the first time, a central composite design was employed to determine optimal nitrogen and carbon concentrations. Nine different concentrations were tested. The center point was tested in five biological replicates, while all other concentrations were tested in duplicates. While the highest biomass (8.00 ± 0.27 g L-1) was reached at C:N of 18.87 (11 g L-1 carbon, 0.583 g L-1 nitrogen), the highest lipid yield (100.5 ± 4.3 mg g-1DCW) was determined using a medium with 11 g L-1 of carbon and only 0.017 g L-1 of nitrogen. The highest carotenoid yield (0.021 ± 0.001 Abs454nm mg-1DCW) was achieved at a C:N of 12 (6 g L-1 carbon, 0.5 g L-1 nitrogen). The presented results provide new insights into the physiology of R. erythropolis under variable nutritional states, enabling the selection of an optimized media composition for the production of valuable oleochemicals or pigments, such as rare odd-chain fatty acids and monocyclic carotenoids.

Biological Control and Mitigation of Aflatoxin Contamination in Commodities

Aflatoxins (AFs) are toxic secondary metabolites produced mostly by Aspergillus species. AF contamination entering the feed and food chain has been a crucial long-term issue for veterinarians, medicals, agroindustry experts, and researchers working in this field. Although different (physical, chemical, and biological) technologies have been developed, tested, and employed to mitigate the detrimental effects of mycotoxins, including AFs, universal methods are still not available to reduce AF levels in feed and food in the last decades. Possible biological control by bacteria, yeasts, and fungi, their excretes, the role of the ruminal degradation, pre-harvest biocontrol by competitive exclusion or biofungicides, and post-harvest technologies and practices based on biological agents currently used to alleviate the toxic effects of AFs are collected in this review. Pre-harvest biocontrol technologies can give us the greatest opportunity to reduce AF production on the spot. Together with post-harvest applications of bacteria or fungal cultures, these technologies can help us strictly reduce AF contamination without synthetic chemicals.

Degradation and Detoxification of Aflatoxin B1 by Tea-Derived Aspergillus niger RAF106

Microbial degradation is an effective and attractive method for eliminating aflatoxin B1 (AFB1), which is severely toxic to humans and animals. In this study, Aspergillus niger RAF106 could effectively degrade AFB1 when cultivated in Sabouraud dextrose broth (SDB) with contents of AFB1 ranging from 0.1 to 4 μg/mL. Treatment with yeast extract as a nitrogen source stimulated the degradation, but treatment with NaNO₃ and NaNO₂ as nitrogen sources and lactose and sucrose as carbon sources suppressed the degradation. Moreover, A. niger RAF106 still degraded AFB1 at initial pH values that ranged from 4 to 10 and at cultivation temperatures that ranged from 25 to 45 °C. In addition, intracellular enzymes or proteins with excellent thermotolerance were verified as being able to degrade AFB1 into metabolites with low or no mutagenicity. Furthermore, genomic sequence analysis indicated that the fungus was considered to be safe owing to the absence of virulence genes and the gene clusters for the synthesis of mycotoxins. These results indicate that A. niger RAF106 and its intracellular enzymes or proteins have a promising potential to be applied commercially in the processing and industry of food and feed to detoxify AFB1.

Novel strategies for degradation of aflatoxins in food and feed: A review

Aflatoxins are toxic secondary metabolites mainly produced by Aspergillus fungi, posing high carcinogenic potency in humans and animals. Dietary exposure to aflatoxins is a global problem in both developed and developing countries especially where there is poor regulation of their levels in food and feed. Thus, academics have been striving over the decades to develop effective strategies for degrading aflatoxins in food and feed. These strategies are technologically diverse and based on physical, chemical, or biological principles. This review summarizes the recent progress on novel aflatoxin degradation strategies including irradiation, cold plasma, ozone, electrolyzed oxidizing water, organic acids, natural plant extracts, microorganisms and enzymes. A clear understanding of the detoxification efficiency, mechanism of action, degradation products, application potential and current limitations of these methods is presented. In addition, the development and future perspective of nanozymes in aflatoxins degradation are introduced.

Statistical optimization of cultural variables for enzymatic degradation of aflatoxin B1 by Panus neostrigosus

The aim of this study is to determine the best aflatoxin B₁ degradation conditions which was optimized using a combination of the Plackett-Burman and Box-Behnken methods with Panus neostrigosus culture filtrate. Panus neostrigosus was grown in a modified Kirk Broth medium to determine optimal degradation conditions. As a result, aflatoxin B₁ was degraded under varying culture conditions. The Plackett-Burman method was designed after sixteen different experiments with fifteen variables. The three most effective variables (Sucrose, yeast extract, wheat bran) were chosen for the Box-Behnken methodology. The aflatoxin B₁ degradation rate was 49% in just 1 h exposure to culture filtrate which was obtained under optimal growth conditions; (g-ml/L) sucrose 10, yeast extract 3, wheat bran 3, soytone 5, KH₂PO₄ 2, MgSO₄.7H₂O 0.5, CaCl₂.H₂O 0.1, ammonium tartrate 2, trace element solution 10; 28 °C of incubation temperature, medium pH 5, 7.5% inoculum rate, 125 rpm of agitation speed, and a twelve-day incubation period. The SDS-PAGE studies show that the enzyme responsible for AFB₁ degradation has 38 kDa molecular weight and has no laccase or MnP activity. To the best of our knowledge, this is the first report for AFB₁ degradation by Panus neostrigosus.

Inhibitory effect of Enterobacter cloacae 3J1EC on Aspergillus flavus 3.4408 growth and aflatoxin production

Aspergillus flavus can easily infect major agricultural products and produce aflatoxin. In this study, we investigated the effect of the biocontrol bacterium Enterobacter cloacae 3J1EC on the growth of A. flavus strain 3.4408. The biocontrol bacterium played a key role in preventing infection by A. flavus. E. cloacae 3J1EC was found to inhibit the growth of A. flavus 3.4408 mycelial pellets and reduce the production of aflatoxin by 96.9%. We found differential expression between the control and the treatment groups in the transcriptome of A. flavus 3.4408. Gene ontology (GO) analysis indicated that E. cloacae 3J1EC induced the down-regulated expression of cellular component and molecular function, while its effects on the up-regulated expression indicated the relationship of biological process and molecular function. Thus, these results suggest that E. cloacae 3J1EC decreased aflatoxin production via down-regulated gene expression in terms of aflatoxin biosynthesis. In summary, E. cloacae 3J1EC can be employed as an alternative for the biological control of A. flavus 3.4408.

Effect of the combined compound probiotics with mycotoxin-degradation enzyme on detoxifying aflatoxin B1 and zearalenone

Aflatoxin B₁ (AFB₁) and zearalenone (ZEA) are the secondary toxic metabolites of fungi which contaminate a wide range of food and feedstuffs. Limiting exposure of humans and livestock to them is very essential. Among numerous methods of mycotoxin-degradation, biodegradation by microorganisms and enzymes is an effective and promising approach to eliminate their hazards. The present study aims to optimize the proportion of different species of beneficial microbes by means of response surface methodology (RSM) and its combination with mycotoxin-degradation enzymes. The results indicated that AFB₁ and ZEA degradation rates were 38.38% and 42.18% by individual Bacillus subtilis (P < 0.05); however, AFB₁ and ZEA degradation rates reached 45.49% and 44.90% (P < 0.05) when three probiotic species such as Bacillus subtilis, Lactobacillus casein and Candida utilis were at a ratio of 1:1:1, corresponding with the predictive value of the RSM model. The further experiment showed that AFB₁ and ZEA degradation rates were 63.95% and 73.51% (P < 0.05) when the compound of three probiotic species was combined with mycotoxin-degradation enzymes from Aspergillus oryzae at a ratio of 3:2. This result indicated that the combination of probiotics with mycotoxin-degradation enzymes is a promising new approach for synchronous detoxification of AFB₁ and ZEA.

Biological Degradation of Aflatoxin B₁ by Cell-Free Extracts of Bacillus velezensis DY3108 with Broad PH Stability and Excellent Thermostability

(1) Background: Aflatoxin contamination in food and grain poses serious problems both for economic development and public health protection, thus leading to a focus on an effective approach to control it; (2) Methods: Aflatoxin B₁ (AFB₁) degrading bacteria were isolated using a medium containing coumarin as the sole carbon source, and the biodegradation of AFB₁ by the isolate was examined by high performance liquid chromatography, and liquid chromatography mass spectrometry; (3) Results: a bacterial strain exhibiting strong AFB1 degradation activity (91.5%) was isolated and identified as Bacillusvelezensis DY3108. The AFB₁ degrading activity was predominantly attributed to the cell-free supernatant of strain DY3108. Besides, it was heat-stable and resistant to proteinase K treatment but sensitive to sodium dodecyl sulfate treatment. The optimal temperature for the maximal degradation of AFB₁ was 80 °C. Even more notable, the supernatant showed a high level of activity over a broad pH (4.0 to 11.0) and exhibited the highest degradation (94.70%) at pH 8.0. Cytotoxicity assays indicated that the degradation products displayed significantly (p < 0.05) lower cytotoxic effects than the parent AFB₁; (4) Conclusions: B.velezensis DY3108 might be a promising candidate for exploitation in AFB₁ detoxification and bioremediation in food and feed matrices.

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.

Rapid biodegradation of aflatoxin B1 by metabolites of Fusarium sp. WCQ3361 with broad working temperature range and excellent thermostability

BACKGROUND

Contamination of food and feed by aflatoxin B1 (AFB1) poses serious economic and health problems worldwide, so the development of biological methods for effective AFB1 degradation is strongly required.

RESULTS

Among three AFB1-degrading microorganisms isolated from moldy peanut, Fusarium sp. WCQ3361 could remove AFB1 extremely effectively, with a degradation ratio of 70.20% after 1 min and 95.38% after 24 h. Its degradation ratio was not much affected by temperature change (0-90 °C) and it also displayed excellent thermostability, maintaining 99.40% residual activity after boiling for 10 min. Since protease K could reduce the AFB1 degradation ratio by 55.15%, it is proposed that the effective component for AFB1 degradation is a protein. The AFB1 degradation ability of Fusarium sp. WCQ3361 was further verified by feed stock detoxification and the MTT test with HepG2 cells. In addition, no degradation products were detected by preliminary liquid chromatography/mass spectrometry, suggesting that AFB1 might be metabolized to products with different chemical characteristics from AFB1.

CONCLUSION

Fusarium sp. WCQ3361 is the first reported AFB1 degradation fungus belonging to the genus Fusarium with broad working temperature range, excellent thermostability and high activity, which provides a potential highly useful solution for dealing with AFB1 contamination in the human diet and animal feed. © 2016 Society of Chemical Industry.

Novel Aflatoxin-Degrading Enzyme from Bacillus shackletonii L7

Food and feed contamination by aflatoxin (AF)B₁ has adverse economic and health consequences. AFB₁ degradation by microorganisms or microbial enzymes provides a promising preventive measure. To this end, the present study tested 43 bacterial isolates collected from maize, rice, and soil samples for AFB₁-reducing activity. The higher activity was detected in isolate L7, which was identified as Bacillus shackletonii. L7 reduced AFB₁, AFB₂, and AFM₁ levels by 92.1%, 84.1%, and 90.4%, respectively, after 72 h at 37 °C. The L7 culture supernatant degraded more AFB₁ than viable cells and cell extracts; and the degradation activity was reduced from 77.9% to 15.3% in the presence of proteinase K and sodium dodecyl sulphate. A thermostable enzyme purified from the boiled supernatant was designated as Bacillus aflatoxin-degrading enzyme (BADE). An overall 9.55-fold purification of BADE with a recovery of 39.92% and an activity of 3.85 × 10³ U·mg-1 was obtained using chromatography on DEAE-Sepharose. BADE had an estimated molecular mass of 22 kDa and exhibited the highest activity at 70 °C and pH 8.0, which was enhanced by Cu2+ and inhibited by Zn2+, Mn2+, Mg2+, and Li⁺. BADE is the major protein involved in AFB₁ detoxification. This is the first report of a BADE isolated from B. shackletonii, which has potential applications in the detoxification of aflatoxins during food and feed processing.

Review on biological degradation of mycotoxins

The worldwide contamination of feeds and foods with mycotoxins is a significant problem. Mycotoxins pose huge health threat to animals and humans. As well, mycotoxins bring enormous economic losses in food industry and animal husbandry annually. Thus, strategies to eliminate or inactivate mycotoxins in food and feed are urgently needed. Traditional physical and chemical methods have some limitations such as limited efficacy, safety issues, losses in the nutritional value and the palatability of feeds, as well as the expensive equipment required to implement these techniques. Biological degradation of mycotoxins has shown promise because it works under mild, environmentally friendly conditions. Aflatoxin (AF), zearalenone (ZEA) and deoxynivalenol (DON) are considered the most economically important mycotoxins in terms of their high prevalence and significant negative effects on animal performance. Therefore, this review will comprehensively describe the biological degradation of AF, ZEA and DON by microorganisms (including fungi and bacteria) and specific enzymes isolated from microbial systems that can convert mycotoxins with varied efficiency to non- or less toxic products. Finally, some strategies and advices on existing difficulties of biodegradation research are also briefly proposed in this paper.

Metabolomics of the bio-degradation process of aflatoxin B1 by actinomycetes at an initial pH of 6.0

Contamination of food and feed by Aflatoxin B1 (AFB1) is a cause of serious economic and health problems. Different processes have been used to degrade AFB1. In this study, biological degradation of AFB1 was carried out using three Actinomycete species, Rhodococcus erythropolis ATCC 4277, Streptomyces lividans TK 24, and S. aureofaciens ATCC 10762, in liquid cultures. Biodegradation of AFB1 was optimised under a range of temperatures from 25 to 40 °C and pH values of 4.0 to 8.0. An initial concentration of 20 µg/mL of AFB1 was used in this study. The amount of AFB1 remaining was measured against time by thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC), coupled with UV and mass spectrometry (LC-MS). All species were able to degrade the AFB1, and no significant difference was found between them. AFB1 remained in the liquid culture for R. erythropolis, S. lividans and S. aureofaciens were 0.81 µg/mL, 2.41 µg/mL and 2.78 µg/mL respectively, at the end of the first 24 h. Degradation occurred at all incubation temperatures and the pH with the optimal conditions for R. erythropolis was achieved at 30 °C and pH 6, whereas for S. lividans and S. aureofaciens the optimum conditions for degradation were 30 °C and pH 5. Analysis of the degradative route indicated that each microorganism has a different way of degrading AFB1. The metabolites produced by R. erythropolis were significantly different from the other two microorganisms. Products of degradation were identified through metabolomic studies by utilizing high-resolution mass spectral data. Mass spectrometric analysis indicated that the degradation of AFB1 was associated with the appearance of a range of lower molecular weight compounds. The pathway of degradation or chemical alteration of AFB1 was followed by means of high resolution Fourier transform mass spectrometry (HR-FTMS) analysis as well as through the MS² fragmentation to unravel the degradative pathway for AFB1. AFB1 bio-degradation was coupled with the accumulation of intermediates of fatty acid metabolism and glycolysis. A plausible mechanism of degradation of AFB1 by Rhodococcus was hypothesized.

Aflatoxin B₁ degradation by a Pseudomonas strain

Aflatoxin B1 (AFB1), one of the most potent naturally occurring mutagens and carcinogens, causes significant threats to the food industry and animal production. In this study, 25 bacteria isolates were collected from grain kernels and soils displaying AFB1 reduction activity. Based on its degradation effectiveness, isolate N17-1 was selected for further characterization and identified as Pseudomonas aeruginosa. P. aeruginosa N17-1 could degrade AFB₁, AFB₂ and AFM₁ by 82.8%, 46.8% and 31.9% after incubation in Nutrient Broth (NB) medium at 37 °C for 72 h, respectively. The culture supernatant of isolate N17-1 degraded AFB₁ effectively, whereas the viable cells and intra cell extracts were far less effective. Factors influencing AFB1 degradation by the culture supernatant were investigated. Maximum degradation was observed at 55 °C. Ions Mn²⁺ and Cu²⁺ were activators for AFB1 degradation, however, ions Mg²⁺, Li⁺, Zn²⁺, Se²⁺, Fe³⁺ were strong inhibitors. Treatments with proteinase K and proteinase K plus SDS significantly reduced the degradation activity of the culture supernatant. No degradation products were observed based on preliminary LC-QTOF/MS analysis, indicating AFB₁ was metabolized to degradation products with chemical properties different from that of AFB₁. The results indicated that the degradation of AFB₁ by P. aeruginosa N17-1 was enzymatic and could have a great potential in industrial applications. This is the first report indicating that the isolate of P. aeruginosa possesses the ability to degrade aflatoxin.