Pathogenicity of Fumonisin-producing and Nonproducing Strains of Aspergillus Species in Section Nigri to Maize Ears and Seedlings.

Species of Aspergillus section Nigri are commonly associated with maize kernels, and some strains can produce fumonisin mycotoxins. However, there is little information about the extent to which these fungi contribute to fumonisin contamination in grain, the damage they cause to maize ears, or their effects on maize seed germination and seedling health. We compared fumonisin-producing and nonproducing strains of A. niger, A. welwitschiae, A. phoenicis, A. tubingensis, and A. carbonarius from the United States and Italy in laboratory and field studies to assess their ability to contribute to fumonisin contamination, to cause maize ear rot, and to affect seed germination and seedling growth. In laboratory experiments, some strains of each Aspergillus species reduced germination or seedling growth, but there was high variability among strains within species. There were no consistent differences between fumonisin-producing and nonproducing strains. In field studies in Iowa and Illinois, strains were variable in their ability to cause ear rot symptoms, but this was independent of the ability of the Aspergillus strains to produce fumonisins. Contamination of grain with fumonisins was not consistently increased by inoculation with Aspergillus strains compared with the control, and was much greater in F. verticillioides-inoculated treatments than in Aspergillus-inoculated treatments. However, the ratio of the FB analogs FB2 and FB1 was altered by inoculation with some Aspergillus strains, indicating that FB2 production by Aspergillus strains occurred in the field. These results demonstrate the pathogenic capabilities of strains of Aspergillus in section Nigri, but suggest that their effects on maize ears and seedlings are not related to their ability to produce fumonisins, and that fumonisin contamination of grain caused by Aspergillus spp. is not as significant as that caused by Fusarium spp.

Genetic variability and fumonisin production by Fusarium proliferatum isolated from durum wheat grains in Argentina.

Fusarium proliferatum is a member of the Fusarium fujikuroi species complex (FFSC) involved in the maize ear rot together with Fusarium verticillioides, which is a very closely related species. Recently, different studies have detected natural fumonisin contamination in wheat kernels and most of them have shown that the main species isolated was F. proliferatum. Fusarium strains obtained from freshly harvested durum wheat samples (2008 to 2011 harvest seasons) from Argentina were characterized through a phylogenetic analysis based on translation elongation factor-1 alpha (EF-1α) and calmodulin (CaM) genes, determination of mating type alleles, and evaluation of fumonisin production capability. The strains were identified as F. proliferatum (72%), F. verticillioides (24%) and other Fusarium species. The ratio of mating type alleles (MAT-1 and MAT-2) obtained for both main populations suggests possible occurrence of sexual reproduction in the wheat fields, although this seems more frequent in F. proliferatum. Phylogenetic analysis revealed greater nucleotide variability in F. proliferatum strains than in F. verticillioides, however this was not related to origin, host or harvest year. The fumonisin-producing ability was detected in 92% of the strains isolated from durum wheat grains. These results indicate that F. proliferatum and F. verticillioides, among the fumonisin producing species, frequently contaminate durum wheat grains in Argentina, presenting a high risk for human and animal health.

Development of loop-mediated isothermal amplification (LAMP) assay for the rapid detection of Penicillium nordicum in dry-cured meat products.

The need of powerful diagnostic tools for rapid, simple, and cost-effective detection of food-borne fungi has become very important in the area of food safety. Currently, several isothermal nucleic acid amplification methods have been developed as an alternative to PCR-based analyses. Loop-mediated isothermal amplification (LAMP) is one of these innovative methods; it requires neither gel electrophoresis to separate and visualize the products nor expensive laboratory equipment and it has been applied already for detection of pathogenic organisms. In the current study, we developed a LAMP assay for the specific detection of Penicillium nordicum, the major causative agent of ochratoxin A contamination in protein-rich food, especially dry-cured meat products. The assay was based on targeting otapksPN gene, a key gene in the biosynthesis of ochratoxin A (OTA) in P. nordicum. Amplification of DNA during the reaction was detected directly in-tube by color transition of hydroxynaphthol blue from violet to sky blue, visible to the naked eye, avoiding further post amplification analyses. Only DNAs isolated from several P. nordicum strains led to positive results and no amplification was observed from non-target OTA and non OTA-producing strains. The assay was able to detect down to 100 fg of purified targeted genomic DNA or 10(2) conidia/reaction within 60 min. The LAMP assay for detection and identification of P. nordicum was combined with a rapid DNA extraction method set up on serially diluted conidia, providing an alternative rapid, specific and sensitive DNA-based method suitable for application directly "on-site", notably in key steps of dry-cured meat production.

Phylogeny, identification and nomenclature of the genus Aspergillus.

Aspergillus comprises a diverse group of species based on morphological, physiological and phylogenetic characters, which significantly impact biotechnology, food production, indoor environments and human health. Aspergillus was traditionally associated with nine teleomorph genera, but phylogenetic data suggest that together with genera such as Polypaecilum, Phialosimplex, Dichotomomyces and Cristaspora, Aspergillus forms a monophyletic clade closely related to Penicillium. Changes in the International Code of Nomenclature for algae, fungi and plants resulted in the move to one name per species, meaning that a decision had to be made whether to keep Aspergillus as one big genus or to split it into several smaller genera. The International Commission of Penicillium and Aspergillus decided to keep Aspergillus instead of using smaller genera. In this paper, we present the arguments for this decision. We introduce new combinations for accepted species presently lacking an Aspergillus name and provide an updated accepted species list for the genus, now containing 339 species. To add to the scientific value of the list, we include information about living ex-type culture collection numbers and GenBank accession numbers for available representative ITS, calmodulin, ß-tubulin and RPB2 sequences. In addition, we recommend a standard working technique for Aspergillus and propose calmodulin as a secondary identification marker.

Aspergillus section Nigri as contributor of fumonisin B(2) contamination in maize.

Fumonisins (FBs), which are carcinogenic mycotoxins, are known to be typically produced by several phytopathogenic fungal species belonging to the genus Fusarium. F. proliferatum and F. verticillioides, two important pathogens of maize worldwide, are the most common species that produce FBs. The main FBs produced by these species are FB1, FB2 and FB3. Moreover, recently, fungal strains belonging to Aspergillus niger have been also reported to produce FBs (in particular, FB2 and FB4). In a survey on maize carried out in Central Italy, 17 maize kernel samples were collected at harvest and analysed for FB1, FB2 and FB3, as well as fungal contamination, with a particular attention to the species-producing FBs. All 17 samples were contaminated by F. verticillioides and/or F. proliferatum at a level ranging from 13% to 100% of kernels. However, 10 out of 17 samples were also contaminated by Aspergillus section Nigri with a range from 6% to 68% of kernels. There was a significant inverse logarithmic relationship between levels of Fusarium and Aspergillus contamination. All samples were contaminated by FBs; FB1 ranged from 0.09 to 30.2 µg g(-1), whereas FB2 ranged from 0.04 to 13.2 µg g(-1). The ratio of FB2/FB1 contamination in the maize samples was evaluated and the highest values occurred in samples contaminated with Aspergillus section Nigri. Thirty strains of Aspergillus section Nigri isolated from these samples were molecularly identified (based on sequences of two housekeeping genes) and analysed for their capability to produce FB2. Among the 30 strains isolated, 12 were identified as Aspergillus welwitschiae (syn. A. awamori) and 18 as A. tubingensis. FB2 was produced by five out of 12 strains of A. welwitschiae within a range of 0.20-5 µg g(-1). This is the first report showing the capability of Aspergillus section Nigri from maize to produce FB2 and its possibility to contribute to FB accumulation in kernels.

Molecular biodiversity of mycotoxigenic fungi that threaten food safety.

Fungal biodiversity is one of the most important contributors to the occurrence and severity of mycotoxin contamination of crop plants. Phenotypic and metabolic plasticity has enabled mycotoxigenic fungi to colonize a broad range of agriculturally important crops and to adapt to a range of environmental conditions. New mycotoxin-commodity combinations provide evidence for the ability of fungi to adapt to changing conditions and the emergence of genotypes that confer enhanced aggressiveness toward plants and/or altered mycotoxin production profiles. Perhaps the most important contributor to qualitative differences in mycotoxin production among fungi is variation in mycotoxin biosynthetic genes. Molecular genetic and biochemical analyses of toxigenic fungi have elucidated specific differences in biosynthetic genes that are responsible for intra- and inter-specific differences in mycotoxin production. For Aspergillus and Fusarium, the mycotoxigenic genera of greatest concern, variation in biosynthetic genes responsible for production of individual families of mycotoxins appears to be the result of evolutionary adaptation. Examples of such variation have been reported for: a) aflatoxin biosynthetic genes in Aspergillus flavus and Aspergillus parasiticus; b) trichothecene biosynthetic genes within and among Fusarium species; and c) fumonisin biosynthetic genes in Aspergillus and Fusarium species. Understanding the variation in these biosynthetic genes and the basis for variation in mycotoxin production is important for accurate assessment of the risks that fungi pose to food safety and for prevention of mycotoxin contamination of crops in the field and in storage.

Phylogenetic characterization and ochratoxin A--fumonisin profile of black Aspergillus isolated from grapes in Argentina.

Aspergillus section Nigri populations isolated from seven growing regions from Argentina were characterized by sequencing in order to identify species responsible for production of ochratoxin A (OTA) and fumonisins (FB(s)). Sequences of genes encoding calmodulin, ß-tubulin, the second largest subunit of RNA polymerase II and translation elongation factor 1 alpha were analysed. The phylogenetic analysis showed the presence of six lineages: A. carbonarius, A. tubingensis, A. niger, A. japonicus, A. homomorphus and A. foetidus grouped in four major clusters. The molecular tools used allowed the identification for the first time of A. homomorphus from vineyards. OTA production confirmed the importance of A. carbonarius as the main ochratoxigenic species isolated and, to a variable degree, of A. niger and A. tubingensis, which were by far the most commonly occurring species on grapes in Argentina. The only strains able to produce OTA and fumonisins (B(2)-B(4)) belong to the A. niger cluster.

Identification, mycotoxin risk and pathogenicity of Fusarium species associated with fig endosepsis in Apulia, Italy.

In a survey carried out on 87 rotted fig fruits samples collected in the Apulia region of Italy, the authors isolated 126 Fusarium strains identified as F. ramigenum (69 strains), F. solani (49), F. proliferatum (five) and three not identified. Investigation on the fertility of the strains belonging to F. proliferatum and F. ramigenum revealed that only strains of F. proliferatum were fertile. The identity of F. ramigenum strains was confirmed by sequencing a portion of the translation elongation factor-1alpha gene. When Fusarium species were analysed for their toxigenicity, 37/69 strains of F. ramigenum produced fusaric acid (FA) up to 525 mg kg(-1); 30 strains produced beauvericin (BEA) up to 190 mg kg(-1); 60 strains produced fumonisin B(1) (FB(1)) and fumonisin B(2) (FB(2)) up to 1575 mg kg(-1) of total FBs; and two strains produced fusaproliferin (FUP) up to 345 mg kg(-1); all five strains of F. proliferatum produced FA at low levels; two strains produced BEA up to 205 mg kg(-1); one strain produced FB(1) and FB(2), 1100 and 470 mg kg(-1), respectively; and one strain produced FUP, 820 mg kg(-1); F. solani (30 strains) produced FA, 13 strains up to 215 mg kg(-1). Few fungal extracts showed high toxicity toward brine shrimp larvae and in some cases in relation to BEA and FA content. A pathogenic assay on fig fruits showed that all three species were pathogenic, with higher virulence of F. ramigenum. These data report for the first time the production of BEA and FB(1)/FB(2) by F. ramigenum and show that it is a main agent of fig endosepsis in Apulia and can contribute to fumonisin contamination of fresh and dried figs.

Detection of Aspergillus carbonarius and other black aspergilli from grapes by DNA OLISA microarray.

Black aspergilli, and particularly Aspergillus carbonarius, are responsible for ochratoxin A production in grapes. Correct identification of these species is essential for toxicological risk assessment in grape and wine. A low-complexity oligonucleotide microarray (OLISA, Apibio, F) based on DNA oligonucleotides probes, obtained from sequences of the calmodulin gene, was set up in order to detect A. carbonarius, A. japonicus/A. aculeatus and A. ibericus isolated from grape. The designed microarray distinguished all Aspergillus species and the detection limit for A. carbonarius was 3.2 pg of DNA as a template for the PCR reaction. This microarray offers a quick and parallel analysis to detect individual Aspergillus species in pure cultures and in naturally contaminated grape samples.

Rapid polymerase chain reaction (PCR)-single-stranded conformational polymorphism (SSCP) screening method for the identification of Aspergillus section Nigri species by the detection of calmodulin nucleotide variations.

Single-stranded conformational polymorphism (SSCP) analysis for genetic diversity studies has been widely applied to detect indirectly sequence differences up to a single base in amplified DNA fragments of the same length, representing an alternative to gene sequencing. In this study SSCP analysis was used to detect sequence variations contained in an about 180-bp region of the calmodulin gene in order to identify Aspergillus section Nigri species. The method described shows that fluorescence-based SSCP analysis by capillary electrophoresis is cheaper and faster than direct sequencing, and suitable for computer-assisted analyses allowing discrimination between the Aspergillus species belonging to the Nigri section: A. aculeatus, Aspergillus 'atypic uniseriate', A. brasiliensis, A. carbonarius, A. ellipticus, A. foetidus, A. heteromorphus, A. ibericus, A. japonicus, A. niger, and A. tubingensis.

Polymerase chain reaction (PCR) identification of Aspergillus niger and Aspergillus tubingensis based on the calmodulin gene.

Aspergillus niger and A. tubingensis, species belonging to section Nigri, are commonly found in plant products and processed food, such as grapes, cereals, coffee, and derived products. These two species are very difficult to differentiate by classical morphological criteria and some isolates are known to produce ochratoxin A. The exact identification of these two species is very important to avoid the overestimation of toxicological contamination and related risks. A polymerase chain reaction (PCR)-based identification and detection assay was developed as a tool to identify A. niger and A. tubingensis, using molecular differences obtained by sequencing the calmodulin gene. Two pairs of species-specific primers were designed and empirically evaluated for PCR identification of A. niger and A. tubingensis. Species-specific PCR products generated by each primer set were 505 bp (A. tubingensis) and 245 bp (A. niger) in length, which could be potentially useful for a multiplex PCR assay. The sensitivity of this assay was about 10 pg DNA in a 25-microl PCR reaction volume, using pure total DNA of the two species. The method described in this study represents a rapid and reliable procedure to assess the presence in food products of two ochratoxigenic species of section Nigri.

Biodiversity of Aspergillus species in some important agricultural products.

The genus Aspergillus is one of the most important filamentous fungal genera. Aspergillus species are used in the fermentation industry, but they are also responsible of various plant and food secondary rot, with the consequence of possible accumulation of mycotoxins. The aflatoxin producing A. flavus and A. parasiticus, and ochratoxinogenic A. niger, A. ochraceus and A. carbonarius species are frequently encountered in agricultural products. Studies on the biodiversity of toxigenic Aspergillus species is useful to clarify molecular, ecological and biochemical characteristics of the different species in relation to their different adaptation to environmental and geographical conditions, and to their potential toxigenicity. Here we analyzed the biodiversity of ochratoxin producing species occurring on two important crops: grapes and coffee, and the genetic diversity of A. flavus populations occurring in agricultural fields. Altogether nine different black Aspergillus species can be found on grapes which are often difficult to identify with classical methods. The polyphasic approach used in our studies led to the identification of three new species occurring on grapes: A. brasiliensis, A. ibericus, and A. uvarum. Similar studies on the Aspergillus species occurring on coffee beans have evidenced in the last five years that A. carbonarius is an important source of ochratoxin A in coffee. Four new species within the black aspergilli were also identified in coffee beans: A. sclerotioniger, A. lacticoffeatus, A. sclerotiicarbonarius, and A. aculeatinus. The genetic diversity within A. flavus populations has been widely studied in relation to their potential aflatoxigenicity and morphological variants L- and S-strains. Within A. flavus and other Aspergillus species capable of aflatoxin production, considerable diversity is found. We summarise the main recent achievements in the diversity of the aflatoxin gene cluster in A. flavus populations, A. parasiticus and the non-toxigenic A. oryzae. Studies are needed in order to characterise the aflatoxin biosynthetic genes in the new related taxa A. minisclerotigenes and A. arachidicola.

Development of a quantitative real-time PCR assay for the detection of Aspergillus carbonarius in grapes.

Aspergillus carbonarius is the main species responsible for the production of ochratoxin A (OTA) in wine grapes. To monitor and quantify A. carbonarious in grapes, a quantitative real-time PCR assay was developed as a possible tool for predicting the potential ochratoxigenic risk. DNA extraction from grape berries was performed by using conventional extraction and clean up through EZNA Hi-bond spin columns. A TaqMan probe was used to quantify A. carbonarius genomic DNA in grape berries samples. An exogenous internal positive control was used to overcome DNA recovery losses due to matrix inhibition. The quantification of fungal genomic DNA in naturally contaminated grape was performed using the TaqMan signal versus spectrophotometrically measured DNA quantities (Log10) calibration curve with a linearity range from 50 to 5 x 10(-4) ng of DNA. A positive correlation (R2=0.92) was found between A. carbonarious DNA content and OTA concentration in naturally contaminated grape samples. This is the first application of TaqMan real-time PCR for identifying and quantifying A. carbonarius genomic DNA occurring in grapes. The rapid DNA extraction method for grapes, together with the commercial availability of reagents and instrumentation, allows to perform a remarkable number of reproducible assays (96-well format) in less than 4 h.

AFLP characterization of Southern Europe population of Aspergillus Section Nigri from grapes.

Members of Aspergillus belonging to Section Nigri are distributed worldwide and are mainly responsible for the ochratoxin A accumulation in grapes and wine, particularly in Southern Europe. Limited information is available on the species composition and genetic variability of black Aspergilli strains occurring on grapes. We analyzed 283 representative strains from the main wine producing European countries collected in 2001-2002 (Italy, France, Spain, Portugal, Greece and Israel) using amplified fragment length polymorphisms (AFLP) technique. Four main groups were obtained by AFLP clustering analysis of these strains and three of them showed a well defined homogeneous population/species with intraspecific homology higher than 48%: Aspergillus carbonarius (105 strains), Aspergillus tubingensis (69 strains), and Aspergillus "uniseriate" (56 strains) with a similarity less than 20% to the Aspergillus japonicus type strain. The fourth cluster, that we called "A. niger like" (44 strains), showed low homology with A. niger type strain (35%) and high internal heterogeneity. Finally, nine strains could not be assigned readily to any of the type strain of the A. nigri Section. These findings indicate that the Aspergillus Section Nigri strains occurring on grapes in Southern Europe represent a complex of species, and some of these are peculiar to grapes.