Occurrence of naphtho-gamma-pyrones- and ochratoxin A-producing fungi in French grapes and characterization of new naphtho-gamma-pyrone polyketide (aurasperone G) isolated from Aspergillus niger C-433

Inhibition of Aβ aggregation by naphtho-γ-pyrone derivatives from a marine-derived fungus, Aspergillus sp. MPUC239

Alzheimer's disease (AD) is an important human disease that mainly causes cognitive impairments. Growing evidence has shown that amyloid-β (Aβ) peptide plays a key role in AD pathogenesis in what is known as the Aβ cascade hypothesis. This hypothesis suggests the importance of suppressing Aβ aggregation and Aβ production. The latter process is governed by β-site APP Cleaving Enzyme1 (BACE1) and γ-secretase. We, therefore, focused on Aβ aggregation inhibitory activity, initially assessing numerous extracts derived from our marine-derived fungus collections. One EtOAc extract derived from an Aspergillus sp. exhibited Aβ aggregation inhibitory activity. Eleven known compounds (1-11) were isolated from CHCl₃ and EtOAc extracts derived from the fungus, and the structures were identified based on MS, NMR, and ECD spectra. Compounds 2, 6, and 10 inhibited Aβ aggregation with IC₅₀ values of 2.8, 3.9, and 8.1 μM, respectively. The protective effect on SH-SY5Y cells against Aβ toxicity was also evaluated, and compounds 6 and 10 significantly alleviated Aβ toxicity. BACE1 inhibitory activity was also examined, and compounds 4, 5, 7, 10, and 11 inhibited BACE1 activity with IC₅₀ values of 14.9, 70.0, 36.5, 28.0, and 72.8 μM, respectively. These data suggest that compound 10 could be useful in AD treatment.

Statistical approach to evaluate effect of temperature and moisture content on the production of antioxidant naphtho-gamma-pyrones and hydroxycinnamic acids by Aspergillus tubingensis in solid-state fermentation

Non-ochratoxigenic Aspergillus tubingensis G131 is a filamentous fungus that can produce naphtho-gamma-pyrones (NγPs), polyketide pigments that exhibit interesting antioxidant properties. This study aims to investigate the effect of two critical parameters, temperature and moisture content on the fungus grown in solid-state fermentation using agricultural by-products (vine shoots and wheat bran) as sole medium. From the kinetic productions of secondary metabolites NγPs (asperpyrone E, dianhydroaurasperone C, fonsecin, fonsecin B and ustilaginoidin A), alkaloids (nigragilin and aspernigrin A), degradation products from the solid medium (β-D-glucose, p-coumaric acid and trans-ethyl ferulate), ergosterol and conidia obtained for different temperatures and moisture contents, a principal component analysis (PCA) was carried out to highlight the production patterns of these compounds. This approach allowed us to determine that fonsecin, the compound of higher interest-exhibiting the most interesting antiradical potential-is particularly more produced at 25 °C and 66% of moisture content. This study underlines the importance of temperature and moisture content on naphtho-gamma-pyrones and hydroxycinnamic acid production using solid-state fermentation and contributes to the development of agroindustrial by-product valorization.

Impact of Spray-Drying on Biological Properties of Chitosan Matrices Supplemented with Antioxidant Fungal Extracts for Wine Applications

Black aspergilli produce many bioactive compounds: enzymes, organic acids, and secondary metabolites. One such fungus, Aspergillus tubingensis G131, isolated from French Mediterranean vineyards, produces secondary metabolites with antioxidant properties that can be extracted with ethanol. In this study, crude antioxidant extracts obtained from A. tubingensis G131 cultures were encapsulated with two types of chitosan matrix. Spray-drying was used to obtain dried particles from a dispersion of fungal crude extracts in a solution of the coating agent chitosan. This process appeared to be an efficient method for obtaining a dry extract with antioxidant activity. Three types of fungal extracts, with different antioxidant capacities, were produced: two different concentrations of crude extract and a semi-purified extract. In this study, the chitosan matrices for encapsulation were chosen on the basis of their antimicrobial activities for wine applications. Classical low molecular weight chitosan was compared with NoBrett Inside^® which is already used to prevent the development of Brettanomyces spp. in wine. The objective of this study was to confirm that both antioxidant (fungal extract) and antimicrobial (chitosan) properties were preserved after spray-drying. The combination of these two properties and the powder formulation of this entirely natural product would make it a good alternative to chemicals, such as sulfites, in the food and wine industries.

Safety of the fungal workhorses of industrial biotechnology: update on the mycotoxin and secondary metabolite potential of Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei

This review presents an update on the current knowledge of the secondary metabolite potential of the major fungal species used in industrial biotechnology, i.e., Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei. These species have a long history of safe use for enzyme production. Like most microorganisms that exist in a challenging environment in nature, these fungi can produce a large variety and number of secondary metabolites. Many of these compounds present several properties that make them attractive for different industrial and medical applications. A description of all known secondary metabolites produced by these species is presented here. Mycotoxins are a very limited group of secondary metabolites that can be produced by fungi and that pose health hazards in humans and other vertebrates when ingested in small amounts. Some mycotoxins are species-specific. Here, we present scientific basis for (1) the definition of mycotoxins including an update on their toxicity and (2) the clarity on misclassification of species and their mycotoxin potential reported in literature, e.g., A. oryzae has been wrongly reported as an aflatoxin producer, due to misclassification of Aspergillus flavus strains. It is therefore of paramount importance to accurately describe the mycotoxins that can potentially be produced by a fungal species that is to be used as a production organism and to ensure that production strains are not capable of producing mycotoxins during enzyme production. This review is intended as a reference paper for authorities, companies, and researchers dealing with secondary metabolite assessment, risk evaluation for food or feed enzyme production, or considerations on the use of these species as production hosts.

Whole-genome sequencing of Aspergillus tubingensis G131 and overview of its secondary metabolism potential

Background

Black Aspergilli represent one of the most important fungal resources of primary and secondary metabolites for biotechnological industry. Having several black Aspergilli sequenced genomes should allow targeting the production of certain metabolites with bioactive properties.

Results

In this study, we report the draft genome of a black Aspergilli, A. tubingensis G131, isolated from a French Mediterranean vineyard. This 35 Mb genome includes 10,994 predicted genes. A genomic-based discovery identifies 80 secondary metabolites biosynthetic gene clusters. Genomic sequences of these clusters were blasted on 3 chosen black Aspergilli genomes: A. tubingensis CBS 134.48, A. niger CBS 513.88 and A. kawachii IFO 4308. This comparison highlights different levels of clusters conservation between the four strains. It also allows identifying seven unique clusters in A. tubingensis G131. Moreover, the putative secondary metabolites clusters for asperazine and naphtho-gamma-pyrones production were proposed based on this genomic analysis. Key biosynthetic genes required for the production of 2 mycotoxins, ochratoxin A and fumonisin, are absent from this draft genome. Even if intergenic sequences of these mycotoxins biosynthetic pathways are present, this could not lead to the production of those mycotoxins by A. tubingensis G131.

Conclusions

Functional and bioinformatics analyses of A. tubingensis G131 genome highlight its potential for metabolites production in particular for TAN-1612, asperazine and naphtho-gamma-pyrones presenting antioxidant, anticancer or antibiotic properties.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4574-4) contains supplementary material, which is available to authorized users.

Bis-naphtho-γ-pyrones from fungi and their bioactivities

Bis-naphtho-γ-pyrones are an important group of aromatic polyketides derived from fungi. They have a variety of biological activities including cytotoxic, antitumor, antimicrobial, tyrosine kinase and HIV-1 integrase inhibition properties, demonstrating their potential applications in medicine and agriculture. At least 59 bis-naphtho-γ-pyrones from fungi have been reported in the past few decades. This mini-review aims to briefly summarize their occurrence, biosynthesis, and structure, as well as their biological activities. Some considerations regarding to synthesis, production, and medicinal and agricultural applications of bis-naphtho-γ-pyrones are also discussed.

Influence of carbon source on growth and mycotoxin production by isolates of Pyrenophora tritici-repentis from wheat

The fungus Pyrenophora tritici-repentis can infect wheat kernels, causing red smudge, and has been shown to produce the anthraquinone mycotoxins emodin, catenarin, and islandicin. The growth of 8 fungal isolates from diverse regions was evaluated on various culture media and was found to be generally slowest on the semisynthetic Fries medium. The choice of carbon source had a significant effect on mycotoxin production, as assessed by high-performance liquid chromatography. The highest emodin concentration (194.18 ± 16.26 µg/g medium) was observed for isolate Alg 3-24 on Fries medium supplemented with fructose, while the highest catenarin concentration (302.54 ±13.92 µg/g medium) was observed for TS93-71B on Fries medium supplemented with starch. Islandicin was not produced by any isolate under the conditions tested. Evaluation of the dynamics of mycotoxin production by isolate 331-2 on V8-potato dextrose agar medium revealed a rapid accumulation of emodin and catenarin during the first week of incubation, followed by a large decline by 14 days. Differences in the growth of and mycotoxin production by isolates of P. tritici-repentis likely resulted from the differential composition of the media and (or) intraspecies variability. Accordingly, the optimization of growth medium should be considered when evaluating the potential of specific isolates for mycotoxin production.

Review of secondary metabolites and mycotoxins from the Aspergillus niger group

Filamentous fungi in the Aspergillus section Nigri (the black aspergilli) represent some of the most widespread food and feed contaminants known but they are also some of the most important workhorses used by the biotechnological industry. The Nigri section consists of six commonly found species (excluding A. aculeatus and its close relatives) from which currently 145 different secondary metabolites have been isolated and/or detected. From a human and animal safety point of view, the mycotoxins ochratoxin A (from A. carbonarius and less frequently A. niger) and fumonisin B(2) (from A. niger) are currently the most problematic compounds. Especially in foods and feeds such as coffee, nuts, dried fruits, and grape-based products where fumonisin-producing fusaria are not a problem, fumonisins pose a risk. Moreover, compounds such as malformins, naptho-gamma-pyrones, and bicoumarins (kotanins) call for monitoring in food, feed, and biotechnology products as well as for a better toxicological evaluation, since they are often produced in large amounts by the black aspergilli. For chemical differentiation/identification of the less toxic species the diketopiperazine asperazine can be used as a positive marker since it is consistently produced by A. tubingensis (177 of 177 strains tested) and A. acidus (47 of 47 strains tested) but never by A. niger (140 strains tested). Naptho-gamma-pyrones are the compounds produced in the highest quantities and are produced by all six common species in the group (A. niger 134 of 140; A. tubingensis 169 of 177; A. acidus 44 of 47; A. carbonarius 40 of 40, A. brasiliensis 18 of 18; and A. ibericus three of three).

Influence of water activity and temperature on growth and mycotoxin production by isolates of Pyrenophora tritici-repentis from wheat

Pyrenophora tritici-repentis is a phytopathogenic fungus that can infect wheat kernels and leaves, causing red smudge and tan spot, respectively. A number of P. tritici-repentis isolates have been shown to be mycotoxigenic, producing the anthraquinone mycotoxins emodin, catenarin and islandicin. The influence of water activity (a(w); 0.75-0.99 a(w)) and temperature (5-45 degrees C) on growth and mycotoxin production by five isolates of P. tritici-repentis was studied. All isolates grew at 0.95-0.99 a(w) and 15-25 degrees C on a wheat-based medium, with three isolates also producing small colonies at 5 degrees C. The optimal growth conditions for all isolates consisted of 0.99 a(w) and 25 degrees C, and growth was significantly reduced at 0.95 a(w) and/or 15 degrees C. Emodin and catenarin were detected in cultures of all isolates, at concentrations ranging from 0.06+/-0.04 to 11.31+/-2.96 microg emodin/g medium, and from 0.09+/-0.06 to 53.42+/-4.36 microg catenarin/g medium. In most isolates, the concentrations of emodin and catenarin declined under suboptimal growth conditions. However, in some isolates, significant increases in the concentrations of both compounds were observed under suboptimal conditions. Islandicin was detected in cultures of only three isolates, at concentrations ranging from 0.07+/-0.05 to 5.69+/-0.76 microg/g medium. The results suggest that growth and mycotoxin formation by P. tritici-repentis are markedly influenced by a(w) and temperature, and that this fungus is hygrophilic. Therefore, infection and contamination of kernels by P. tritici-repentis are likely to occur in the field rather than in storage. To our knowledge, this is the first study on the effect of environmental factors on mycelial growth and mycotoxin production by P. tritici-repentis.