Significance of Aspergillus niger aggregate species as contaminants of food products in Spain regarding their occurrence and their ability to produce mycotoxins

Isolation and Characterization of Paenibacillus polymyxa B7 and Inhibition of Aspergillus tubingensis A1 by Its Antifungal Substances

Screening of Bacillus with antagonistic effects on paddy mold pathogens to provide strain resources for biological control of mold in Oryza sativa L. screening of Bacillus isolates antagonistic towards Aspergillus tubingensis from rhizosphere soil of healthy paddy; classification and identification of antagonistic strains by biological characteristics and 16S rDNA sequence analysis; transcriptome sequencing after RNA extraction from Bacillus-treated Aspergillus tubingensis; and extraction of inhibitory crude proteins of Bacillus by ammonium sulfate precipitation; inhibitory crude protein and Bacillus spp. were treated separately for A. tubingensis and observed by scanning electron microscopy (SEM). An antagonistic strain of Bacillus, named B7, was identified as Paenibacillus polymyxa by 16S rDNA identification and phylogenetic evolutionary tree comparison analysis. Analysis of the transcriptome results showed that genes related to secondary metabolite biosynthesis such as antifungal protein were significantly downregulated. SEM results showed that the mycelium of A. tubingensis underwent severe rupture after treatment with P. polymyxa and antifungal proteins, respectively. In addition, the sporocarp changed less after treatment with P. polymyxa, and the sporangium stalks had obvious folds. P. polymyxa B7 has a good antagonistic effect against A. tubingensis and has potential for biocontrol applications of paddy mold pathogens.

Current status of secondary metabolite pathways linked to their related biosynthetic gene clusters in Aspergillus section Nigri

Covering: up to the end of 2021Aspergilli are biosynthetically 'talented' micro-organisms and therefore the natural products community has continually been interested in the wealth of biosynthetic gene clusters (BGCs) encoding numerous secondary metabolites related to these fungi. With the rapid increase in sequenced fungal genomes combined with the continuous development of bioinformatics tools such as antiSMASH, linking new structures to unknown BGCs has become much easier when taking retro-biosynthetic considerations into account. On the other hand, in most cases it is not as straightforward to prove proposed biosynthetic pathways due to the lack of implemented genetic tools in a given fungal species. As a result, very few secondary metabolite biosynthetic pathways have been characterized even amongst some of the most well studied Aspergillus spp., section Nigri (black aspergilli). This review will cover all known biosynthetic compound families and their structural diversity known from black aspergilli. We have logically divided this into sub-sections describing major biosynthetic classes (polyketides, non-ribosomal peptides, terpenoids, meroterpenoids and hybrid biosynthesis). Importantly, we will focus the review on metabolites which have been firmly linked to their corresponding BGCs.

Resistance of Black Aspergilli Species from Grape Vineyards to SDHI, QoI, DMI, and Phenylpyrrole Fungicides

Fungicide applications constitute a management practice that reduces the size of fungal populations and by acting as a genetic drift factor, may affect pathogen evolution. In a previous study, we showed that the farming system influenced the population structure of the Aspergillus section Nigri species in Greek vineyards. The current study aimed to test the hypothesis that the differences in the population structure may be associated with the selection of fungicide-resistant strains within the black aspergilli populations. To achieve this, we determined the sensitivity of 102, 151, 19, and 22 for the A. uvarum, A. tubingensis, A. niger, and A. carbonarious isolates, respectively, originating either from conventionally-treated or organic vineyards to the fungicides fluxapyroxad-SDHIs, pyraclostrobin-QoIs, tebuconazole-DMIs, and fludioxonil-phenylpyrroles. The results showed widespread resistance to all four fungicides tested in the A. uvarum isolates originating mostly from conventional vineyards. In contrast, all the A. tubingensis isolates tested were sensitive to pyraclostrobin, while moderate frequencies of only lowly resistant isolates were identified for tebuconazole, fludioxonil, and fluxapyroxad. Sequencing analysis of the corresponding fungicide target encoding genes revealed the presence of H270Y, H65Q/S66P, and G143A mutations in the sdhB, sdhD, and cytb genes of A. uvarum resistant isolates, respectively. No mutations in the Cyp51A and Cyp51B genes were detected in either the A. uvarum or A. tubingensis isolates exhibiting high or low resistance levels to DMIs, suggesting that other resistance mechanisms are responsible for the observed phenotype. Our results support the initial hypothesis for the contribution of fungicide resistance in the black aspergilli population structure in conventional and organic vineyards, while this is the first report of A. uvarum resistance to SDHIs and the first documentation of H270Y or H65Q/S66P mutations in sdhB, sdhD, and of the G143A mutation in the cytb gene of this fungal species.

Genome-Based Analysis of Aspergillus niger Aggregate Species from China and Their Potential for Fumonisin B2 and Ochratoxin A Production

Based on entire genome sequencing, this study focused on the classification of Aspergillus niger aggregation species and investigated their potential for fumonisin B₂ (FB₂) and ochratoxin A (OTA) production. In the current study, 22 strains were used, namely 17 A. niger strains, four A. welwitschiae strains, and one A. lacticoffeatus (a synonym of A. niger) strain. Traditional multigene phylogenetic analysis, average nucleotide identity analysis (ANI), and the whole-genome single-nucleotide polymorphism (SNP) analyses were used to reconfirm the taxonomic status of A. niger, A. welwitschiae, and A. lacticoffeatus. The ability of A. niger to produce FB₂ and OTA on five culture substrates was determined, and the association between FB₂ and OTA gene clusters and toxin-producing abilities was explored. The results revealed that the ANI method could distinguish A. niger from A. welwitschiae, with an ANI value of < 98%. The SNP-based phylogenetic analysis suggested that A. niger and A. welwitschiae were two independent phylogenetic species. The ANI, SNP, and multigene phylogenetic analysis supported previous findings that A. lacticoffeatus was a synonymous species of A. niger. Aspergillus niger strains exhibited the varied potential of producing FB₂ and OTA on different culture media. The A. niger genome sequence analysis revealed no significant difference in fumonisin gene clusters between FB₂-nonproducing isolates and FB₂-producing isolates, and the integrity of the ochratoxin biosynthesis genes cluster was clearly associated with OTA production. In conclusion, gene sequencing can be useful in assessing A. niger's ability to produce OTA, but it cannot reliably predict its ability to produce FB₂.

Exploitation of the Antibacterial Properties of Photoactivated Curcumin as ‘Green’ Tool for Food Preservation

In the search for non-chemical and green methods to counteract the bacterial contamination of foods, the use of natural substances with antimicrobial properties and light irradiation at proper light waves has been extensively investigated. In particular, the combination of both techniques, called photodynamic inactivation (PDI), is based on the fact that some natural substances act as photosensitizers, i.e., produce bioactive effects under irradiation. Notably, curcumin is a potent natural antibacterial and effective photosensitizer that is able to induce photodynamic activation in the visible light range (specifically for blue light). Some practical applications have been investigated with particular reference to food preservation from bacterial contaminants.

Mapping Aspergillus niger Metabolite Biomarkers for In Situ and Early Evaluation of Table Grapes Contamination

The Aspergillus niger exometabolome was recently investigated using advanced gas chromatography in tandem with multivariate analysis, which allowed a metabolite biomarker pattern to be proposed. Microbial metabolomics patterns have gained enormous relevance, mainly due to the amount of information made available, which may be useful in countless processes. One of the great challenges in microbial metabolomics is related to applications in more complex systems of metabolomics information obtained from studies carried out in culture media, as complications may occur due to the dynamic nature of biological systems. Thus, the main objective of this research was to evaluate the applicability of the A. niger metabololite biomarkers pattern for in situ and early evaluation of table grapes contamination, used as study model. A. niger is a ubiquitous fungus responsible for food contamination, being reported as one of the main agents of the black mold disease, a serious post-harvest pathology of table grapes. This work included analysis from 1 day of growth time of pure A. niger cultures, A. niger cultures obtained from previously contaminated grapes, and finally, an in situ solid-phase microextraction (SPME) approach directly on previously contaminated table grapes. Supervised multivariate analysis was performed which revealed that after 1 day of inoculation it was possible to detect A. niger biomarkers, which can be extremely useful in making this type of method possible for the rapid detection of food contamination. The results obtained confirm the potential applicability of the pattern of A. niger biomarkers for early detection of the fungi (after 1 day of contamination), and may be further explored for access food susceptibility to fungi contamination, based on direct analysis of the food item.

Biotechnological valorization of cashew apple juice for the production of citric acid by a local strain of Aspergillus niger LCFS 5

Background

This work investigates the production of citric acid from cashew apple juice, an abundant waste in the processing of cashew, using a local strain of Aspergillus niger and the application of the citric acid as a coagulant for the production of soy cheese. Fungal isolates were obtained from a cashew plantation in Ogbomoso, Nigeria, using potato dextrose agar. Further screening was undertaken to determine the qualitative strength of acid production by the fungi on Czapek-Dox agar supplemented with bromocresol green, with the development of yellow zone taken as an indication of citric acid production. Thereafter, the best producing strain was cultivated in a cashew apple juice medium.

Results

Out of 150 fungal isolates generated from the cashew plantation, 92 (61.3%), 44 (29.3%) and 14 (9.3%) were obtained from cashew fruits, soil and cashew tree surfaces, respectively. Different strains of fungi isolated include Aspergillus niger, A. flavus, A. foetidus, A. heteromorphus, A. nidulans and A. viridinutans. The isolates produced yellow zonation of 0.4–5.5 cm on modified Czapek-Dox agar; the highest was observed for a strain of A. niger LCFS 5, which was identified using molecular tools. In the formulated cashew apple juice medium, the citric acid yield of LCFS 5 ranged 16.0–92.8 g/l with the peak obtained on the 10th day of fermentation. The citric acid produced was recovered using the double precipitation method with Ca(OH)₂ and H₂SO₄ having ≈ 70% purity of citric acid on HPLC. The citric acid acted as a coagulant to produce soy cheese with 66.67% acceptability by panelists.

Conclusion

This work has extended the frontiers of valorization of cashew waste by a strain of A. niger to produce citric acid in high yield, with potential application in food industries.

A preliminary study on mycobiota and ochratoxin a contamination in commercial palm dates (Phoenix dactylifera)

The occurrence of mycotoxins and mycotoxigenic fungi in palm dates has not been thoroughly documented. The aims of the present study were to identify the mycobiota present in commercial date samples (n = 19), to determine the ability of the isolated fungi to produce mycotoxins, and to determine and quantify the presence of OTA in date fruits. The majority of products originated from Tunisia (n = 14) and Algeria (n = 3). The dominant fungal species were Aspergillus niger, Aspergillus tubingensis and Aspergillus flavus which were most frequently found in premium quality and organic produce, produced without chemical preservatives. OTA was found in only one sample at a concentration of 0.75 µg/kg, as determined by HPLC with fluorescence detection. Although this preliminary study did not find elevated levels of OTA, its presence in one out of 19 samples indicates that palm dates for human consumption require continuous and stringent control, in order to prevent contaminated produce from entering the market.

Identification of a Novel Biosynthetic Gene Cluster in Aspergillus niger Using Comparative Genomics

Previously, DNA microarrays analysis showed that, in co-culture with Bacillus subtilis, a biosynthetic gene cluster anchored with a nonribosomal peptides synthetase of Aspergillus niger is downregulated. Based on phylogenetic and synteny analyses, we show here that this gene cluster, NRRL3_00036-NRRL3_00042, comprises genes predicted to encode a nonribosomal peptides synthetase, a FAD-binding domain-containing protein, an uncharacterized protein, a transporter, a cytochrome P450 protein, a NAD(P)-binding domain-containing protein and a transcription factor. We overexpressed the in-cluster transcription factor gene NRRL3_00042. The overexpression strain, NRRL3_00042OE, displays reduced growth rate and production of a yellow pigment, which by mass spectrometric analysis corresponds to two compounds with masses of 409.1384 and 425.1331. We deleted the gene encoding the NRRL3_00036 nonribosomal peptides synthetase in the NRRL3_00042OE strain. The resulting strain reverted to the wild-type phenotype. These results suggest that the biosynthetic gene cluster anchored by the NRRL3_00036 nonribosomal peptides synthetase gene is regulated by the in-cluster transcriptional regulator gene NRRL3_00042, and that it is involved in the production of two previously uncharacterized compounds.

Mycotoxins in artisanal beers: An overview of relevant aspects of the raw material, manufacturing steps and regulatory issues involved

The consumption of artisanal beer has increased worldwide. Artisanal beers can include malted or unmalted wheat, maize, rice and sorghum, in addition to the basic ingredients. These grains can be infected by toxigenic fungi in the field or during storage and mycotoxins can be produced if they find favorable conditions. Mycotoxins may not be eliminated throughout the beer brewing and be detected in the final product. In addition, modified mycotoxins may also be formed during beer brewing. This review compiles relevant information about mycotoxins produced by Aspergillus, Fusarium and Penicillium in raw material of artisanal beer, as well as updates information about the production and fate of mycotoxins during the beer brewing process. Findings highlight that malting conditions favor the production of mycotoxins by the fungi contaminating cereals. Therefore, good agricultural and postharvest mitigation strategies are the most effective options for preventing the growth of toxigenic fungi and the production of mycotoxins in cereals. However, the final concentration of mycotoxin in artisanal beer is difficult to predict as it depends on the initial concentration contained in the raw material and the processing conditions. The current lack of limits of mycotoxins in artisanal beer underestimates possible risks to human health. In addition, modified mycotoxins, not detected by conventional methods, may be formed in artisanal beers. Maximum tolerated limits for these contaminants must be urgently established based on scientific data about transfer of mycotoxins throughout the artisanal beer brewery process.

Ochratoxin A and related fungi in Brazilian black pepper (Piper nigrum L.)

Ochratoxin A (OTA) is a mycotoxin with nephrotoxic, genotoxic, teratogenic and carcinogenic properties, produced by several species of Aspergillus, mainly those belonging to the A. section Circumdati and A. section Nigri. Although this toxin has been detected in spices and condiments, in black pepper (Piper nigrum L.) few studies have investigated the mycobiota (based on a molecular approach) and the presence of OTA in this food. The aim of this study was to investigate the presence of potentially ochratoxigenic species and ochratoxin A in black pepper marketed in Brazil, one of the largest producers in the world. A total of 60 samples of black pepper (29 in powder and 31 in grain) were collected in markets. The presence of OTA was investigated in black pepper samples using High-Performance Liquid Chromatography (HPLC), OTA was detected in 55% of the samples, with levels ranging from 0.05 to 13.15 μg/kg, all of which were below the Brazilian legal tolerances. A. section Nigri and A. section Circumdati were found in 80% of the samples, but the species of A. section Nigri were significantly more frequent than those of A. section Circumdati. The potential for OTA production by fungal isolates was tested using the agar plug technique and confirmed by HPLC. Among the isolates belonging to A. section Nigri (n = 1,083) and A. section Circumdati (n = 129), 3.7% and 3.8%, respectively, were able to produce OTA in Yeast Extract Sucrose Agar (YESA). A total of 25 strains from A. section Circumdati and 64 from A. section Nigri were identified using molecular data. The following potentially ochratoxigenic species were found in black pepper: A. niger, A. welwitschiae, A. carbonarius, A. westerdijkiae and A. ochraceus. The occurrence of these species denotes the need for continuous monitoring of black pepper by regulatory bodies in order to safeguard consumers' health.

The Genomic Regions That Contain Ochratoxin A Biosynthetic Genes Widely Differ in Aspergillus Section Circumdati Species

Aspergillus section Circumdati includes 27 species, some of which are considered ochratoxin A (OTA) producers. However, there is considerable controversy about their potential OTA synthesis ability. In this work, the complete genomes of 13 species of Aspergillus section Circumdati were analyzed in order to study the cluster of OTA biosynthetic genes and the region was compared to those previously reported in A. steynii and A. westerdijkiae. The results obtained reveal that the genomes of some species in this section, including A. affinis, A. cretensis, A. elegans, A. muricatus, A. pulvericola, A. roseoglobulosus, and A. subramanianii, contain a potentially functional OTA biosynthetic cluster. Therefore, they might be able to synthesize the toxin. On the contrary, A. melleus, A. ochraceus, A. ostianus, A. persii, A. sclerotiorum, A. sesamicola, and A. westlandensis contain a truncated version of the cluster that lacks many of the genes involved in OTA biosynthesis, which might be related to their inability to produce OTA. The gain/loss pattern is different in all species, which suggests that the genetic evolution of this region might be due to independent events.

Black aspergilli in Brazilian onions: From field to market

The occurrence of black aspergilli in onions has been reported as frequent, and this group of fungi harbors potentially toxigenic species. In addition, Aspergillus niger has been reported as the causative agent of black mold rot, an important postharvest disease that causes damage throughout the world. Brazil stands out as one of the world's largest onion producers. However, few studies have been conducted to investigate the mycobiota in Brazilian onions. For this reason, we investigated the mycobiota of 48 market (n = 25) and field (n = 23) onion bulb samples. Nineteen soil samples were collected from the same fields and evaluated. In field onions and soil samples, Penicillium spp. was the prevalent fungal group, whereas in market samples A. section Nigri was the most frequent group. Due to the taxonomic complexity of this group, species identification was supported by phylogenetic data (CaM gene). A. welwitschiae was the most prevalent species in market samples. Black aspergillus strains were evaluated for fumonisin B₂ (FB₂) and ochratoxin A (OTA) production. Overall, 53% and 2.2% of the strains produced FB₂ and OTA, respectively. The occurrence of FB₂ and OTA was also investigated in onion bulb samples but none showed contamination with these mycotoxins.

A Comprehensive Study on the Occurrence of Mycotoxins and Their Producing Fungi during the Maize Production Cycle in Spain

Mycotoxin contamination is one of the main problems affecting corn production, due to its significant risk to human and animal health. The Fusarium and Aspergillus species are the main producers of mycotoxins in maize, infecting both pre-harvest and during storage. In this work, we evaluated the presence of mycotoxins and their producing species along maize production cycles in three different stages (anthesis, harvest, and storage) during three consecutive seasons (2016-2018). Fungal occurrences were studied using species-specific PCR protocols, whereas mycotoxin levels were determined by LC-MS/MS. Fumonisin-producing Fusarium species (F. verticillioides and F. proliferatum), as well as the aflatoxin producer Aspergillus flavus, were the most predominant species at all stages; although, during some seasons, the presence of F. graminearum and A. niger aggregate species were also identified. Contrastingly, fumonisins were the only mycotoxins detected and levels were always under legal regulations. The results presented here demonstrate that even when fungal contamination occurs at the early stages of the maize production cycle, the application of good agricultural and storage practices might be crucial to ensure mycotoxin-free grains.

Rice husk as a source for fungal biopesticide production by solid-state fermentation using B. bassiana and T. harzianum

Solid-state fermentation using rice husk as substrate with either Beauveria bassiana or Trichoderma harzianum was conducted on batch reactors at laboratory scale to establish optimal conditions for spore production. Time course tests were performed to determine maximum spore production time, which was 7.7 days for Beauveria bassiana and 5.7 days for Trichoderma harzianum. The effect of moisture, inoculum concentration, airflow rate, temperature and C/N ratio on spore production was evaluated by two Box-Behnken experimental designs. Final spore concentrations ranged from 2.0 × 10⁸ to 2.0 × 10⁹ spores g^-1 dry matter. Main factors influencing spore production were moisture (optimum values of 55-60% for Trichoderma harzianum and 65-70 for Beauveria bassiana) and temperature (25 °C). The effect of mixing enhanced Trichoderma harzianum spore production while influencing negatively in the case of Beauveria bassiana. Robustness of the process has been demonstrated through statistical analysis using box-plots.

Analysis of the Carry-Over of Ochratoxin A from Feed to Milk, Blood, Urine, and Different Tissues of Dairy Cows Based on the Establishment of a Reliable LC-MS/MS Method

A rapid and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for simultaneous determination of ochratoxin A (OTA) and its metabolite ochratoxin α (OTα), for the first time, in dairy cow plasma, milk, urine, heart, liver, spleen, lung, and kidney. The established method was extensively validated by determining the linearity (R² ≥ 0.990), sensitivity (lower limit of quantification, 0.1-0.2 ng mL^-1), recovery (75.3-114.1%), precision (RSD ≤ 13.6%), and stability (≥83.0%). Based on the methodological advances, the carry-over of OTA was subsequently studied after oral administration of 30 μg/kg body weight OTA to dairy cows. As revealed, OTA and OTα were detected in urine, with maximal concentrations of 1.8 ng mL^-1 and 324.6 ng mL^-1, respectively, but not in milk, plasma, or different tissues, verifying the protection effects of rumen flora against OTA exposure for dairy cows. Moreover, 100 fresh milk samples randomly collected from different supermarkets in Shanghai were also analyzed, and no positive samples were found, further proving the correctness of the in vivo biotransformation results. Thus, from the currently available data, regarding OTA contamination issues on dairy cows, no significant health risks were related to OTA exposure due to the consumption of these products.