Investigation of diversity and dominance of fungal biota in stored wheat grains from governmental warehouses in West Bengal, India

Mycobiome mediates the interaction between environmental factors and mycotoxin contamination in wheat grains

Environmental factors significantly impact grain mycobiome assembly and mycotoxin contamination. However, there is still a lack of understanding regarding the wheat mycobiome and the role of fungal communities in the interaction between environmental factors and mycotoxins. In this study, we collected wheat grain samples from 12 major wheat-producing provinces in China during both the harvest and storage periods. Our aim was to evaluate the mycobiomes in wheat samples with varying deoxynivalenol (DON) contamination levels and to confirm the correlation between environmental factors, the wheat mycobiome, and mycotoxins. The results revealed significant differences in the wheat mycobiome and co-occurrence network between contaminated and uncontaminated wheat samples. Fusarium was identified as the main differential taxon responsible for inducing DON contamination in wheat. Correlation analysis identified key factors affecting mycotoxin contamination. The results indicate that both environmental factors and the wheat mycobiome play significant roles in the production and accumulation of DON. Environmental factors can affect the wheat mycobiome assembly, and wheat mycobiome mediates the interaction between environmental factors and mycotoxin contamination. Furthermore, a random forest (RF) model was developed using key biological indicators and environmental features to predict DON contamination in wheat with accuracies exceeding 90 %. The findings provide data support for the accurate prediction of mycotoxin contamination and lay the foundation for the research on biological control technologies of mycotoxin through the assembly of synthetic microbial communities.

Potential fungicidal and antiaflatoxigenic effects of cinnamon essential oils on Aspergillus flavus inhabiting the stored wheat grains

Wheat is one of the essential crops for the human and animal nutrition, however, contamination with aflatoxigenic fungi, due to the improper storage conditions and high humidity, was the main global threats. So, preventing the growth of aflatoxigenic fungi in stored wheat grains, by using different essential oils was the main objective of this work. Aspergillus flavus EFBL-MU12 PP087400, EFBL-MU23 PP087401 and EFBL-MU36 PP087403 isolates were the most potent aflatoxins producers inhabiting wheat grains. The effect of storage conditions of wheat grains "humidity, temperature, incubation period, and pH" on growth of A. flavus, was assessed by the response surface methodology using Plackett-Burman design and FCCD. The highest yield of aflatoxins EFBL-MU12 B1 and B2 by A. flavus grown on wheat grains were 145.3 and 7.6 μg/kg, respectively, at incubation temperature 35°C, 16% moisture contents, initial pH 5.0, and incubated for 14 days. The tested oils had a powerful antifungal activity for the growth and aflatoxins production by A. flavus in a concentration-dependent manner. Among these oils, cinnamon oil had the highest fungicidal activity for A. flavus at 0.125%, with about 85-90 % reduction to the aflatoxins B1 and B2, conidial pigmentation and chitin contents on wheat grains. From the SEM analysis, cinnamon oils had the most deleterious effect on A. flavus with morphological aberrations to the conidial heads, vegetative mycelia, alteration in conidiophores identity, hyphae shrank, and winding. To emphasize the effect of the essential oils on the aflatoxins producing potency of A. flavus, the molecular expression of the aflatoxins biosynthetic genes was estimated by RT-qPCR. The molecular expression of nor-1, afLR, pKsA and afLJ genes was suppressed by 94-96%, due to cinnamon oil at 0.062% compared to the control. Conclusively, from the results, cinnamon oils followed by the peppermint oils displayed the most fungicidal activity for the growth and aflatoxins production by A. flavus grown on wheat grains.

Interactions among the composition changes in fungal communities and the main mycotoxins in simulated stored wheat grains

BACKGROUND

There are significant food safety risks associated with wheat spoilage due to fungal growth and mycotoxin contamination. Nevertheless, a few studies have examined how stored wheat grain microbial communities and mycotoxins vary in different storage conditions. In this study, changes in deoxynivalenol (DON) and deoxynivalenol-3-glucoside (D3G) content were measured with ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), and an amplicon sequence analysis of fungi was performed on stored wheat grains from different storage conditions using high-throughput sequencing. The detailed interactions among the composition changes in the fungal community and the DON content of simulated stored wheat grains were also analyzed.

RESULTS

Alternaria, Fusarium, Mrakia, and Aspergillus were the core fungal taxa, and the fungal communities of samples stored under different conditions were observed to be different. Aspergillus relative abundances increased, whereas Fusarium decreased. This led to an increase in the content of DON. The content of DON increased about 67% with 12% moisture and at 25 °C after 2 months of storage, which was influenced by the stress response of Fusarium. Correlations in fungal and mycotoxins changes were observed. There may be potential value in these findings for developing control strategies to prevent mildew infestations and mycotoxins contamination during grain storage.

CONCLUSION

In storage, the more the fungal community composition and the relative abundance of Fusarium change, the more mycotoxins will be produced. We should therefore reduce competition between fungal communities through pre-storage treatment and through measures during storage. © 2023 Society of Chemical Industry.

Fungal Diversity in Barley Under Different Storage Conditions

The diversity of fungi in barley in simulated storage environments was analyzed. Barley was stored at different temperatures (15, 25, 35°C) and relative humidity (55, 65, 75, 85 RH) for 180 and 360 days. Alpha diversity, beta diversity, species composition, and species differences were analyzed using Illumina HiSeq technology. The fungal communities in all barley samples before and after storage belonged to 3 phyla, 18 classes, 39 orders, 71 families, 103 genera, and 152 species. The relative abundance of the dominant phylum Ascomycota was 77.98–99.19%. The relative abundance of Basidiomycota was 0.77–21.96%. At the genus level, the dominant genera of fungi in barley initially included Fusarium, Aspergillus, Microdochium, Alternaria, and Epicoccum. After 360 days of storage, the dominant genera became Epicoccum, Alternaria, Bipolar, Cladosporium, Fusarium, and Aspergillus. According to Venn diagrams and principal coordinates analysis, the fungal community diversity in barley initially was much higher than in barley stored at different temperatures and humidity. The application of PLS-DA could accurately distinguish between barley stored for 180 and 360 days. Some high-temperature and high-humidity environments accelerated storage. The dominant genera differed in different storage conditions and constantly changed with increasing storage duration. Epicoccum was one of the dominant genera after longer storage periods. This study provides theoretical support for optimizing safe storage conditions in barley.

Antibody conjugated magnetic nanoparticle based colorimetric assay for the detection and quantification of aflatoxin B1 in wheat grains

Aflatoxin B1 (AFB1) is a most potent carcinogenic secondary metabolite produced by Aspergillus flavus. As a food safety concern, development of a rapid, cost effective, sensitive and easy to use method for the detection of aflatoxin is of prime requirement. In this study, AFB1 was conjugated with bovine serum albumin (BSA), and AFB1-BSA conjugate was purified by HPLC. Purification was confirmed by UV-Vis spectroscopy, FTIR and MALDI-TOF mass spectrometry. The polyclonal antibody was raised against AFB1-BSA conjugate in rabbit and purified by protein A sepharose and BSA sepharose affinity columns. Iron oxide nanoparticles (MNPs) were synthesised by co-precipitation method and their surface was functionalised with (3-aminopropyl) triethoxysilane (APTES). Size of APTES conjugated MNPs was determined by electron microscopy, and characterised by several biophysical techniques. The purified anti-AFB1 antibody was conjugated with surface functionalised MNPs and the conjugation was confirmed by determining the sizes of free and antibody conjugated MNPs by field emission scanning electron microscope where increase of particle sizes from 10-20 to 40-50 nm was observed due to antibody conjugation. Anti-AFB1 antibody conjugated MNPs were used for capturing AFB1 from the aflatoxin spiked wheat grains with a recovery percentage of more than 80% and used effectively five times. The captured AFB1 was then quantified by a sensitive colorimetric assay where colourless AFB1 was first converted into coumaric acid by NaOH. Subsequently, coumaric acid reacted with 2,6-dibromoquinone-4-chloroimide (DBQC) to a green-coloured indophenol product which was quantified spectrophotometrically. AFB1 contamination as low as 2 μg/kg in wheat grains was detected by the developed technique suggesting its potential application for both qualitative and quantitative analysis of aflatoxins present in feed and food materials.

Recent progress in mycotoxins detection based on surface-enhanced Raman spectroscopy

Mycotoxins are toxic compounds naturally produced by certain types of fungi. The contamination of mycotoxins can occur on numerous foodstuffs, including cereals, nuts, fruits, and spices, and pose a major threat to humans and animals by causing acute and chronic toxic effects. In this regard, reliable techniques for accurate and sensitive detection of mycotoxins in agricultural products and food samples are urgently needed. As an advanced analytical tool, surface-enhanced Raman spectroscopy (SERS), presents several major advantages, such as ultrahigh sensitivity, rapid detection, fingerprint-type information, and miniaturized equipment. Benefiting from these merits, rapid growth has been observed under the topic of SERS-based mycotoxin detection. This review provides a comprehensive overview of the recent achievements in this area. The progress of SERS-based label-free detection, aptasensor, and immunosensor, as well as SERS combined with other techniques, has been summarized, and in-depth discussion of the remaining challenges has been provided, in order to inspire future development of translating the techniques invented in scientific laboratories into easy-to-operate analytic platforms for rapid detection of mycotoxins.