Molecular characterization of atoxigenic strains for biological control of aflatoxins in Nigeria

Species Identification and Mycotoxigenic Potential of Aspergillus Section Flavi Isolated from Maize Marketed in the Metropolitan Region of Asunción, Paraguay

Zea mays var. amylacea and Zea mays var. indurata are maize ecotypes from Paraguay. Aspergillus section Flavi is the main spoilage fungus of maize under storage conditions. Due to its large intraspecific genetic variability, the accurate identification of this fungal taxonomic group is difficult. In the present study, potential mycotoxigenic strains of Aspergillus section Flavi isolated from Z. mays var. indurata and Z. mays var. amylacea that are marketed in the metropolitan region of Asunción were identified by a polyphasic approach. Based on morphological characters, 211 isolates were confirmed to belong to Aspergillus section Flavi. A subset of 92 strains was identified as Aspergillus flavus by mass spectrometry MALDI-TOF and the strains were classified by MALDI-TOF MS into chemotypes based on their aflatoxins and cyclopiazonic acid production. According to the partial sequencing of ITS and CaM genes, a representative subset of 38 A. flavus strains was confirmed. Overall, 75 A. flavus strains (86%) were characterized as producers of aflatoxins. The co-occurrence of at least two mycotoxins (AF/ZEA, FUM/ZEA, and AF/ZEA/FUM) was detected for five of the Z. mays samples (63%). Considering the high mycological bioburden and mycotoxin contamination, maize marketed in the metropolitan region of Asunción constitutes a potential risk to food safety and public health and requires control measures.

Molecular Characterization of Aspergillus flavus Strains Isolated from Animal Feeds

Aflatoxin (AF)-producing fungi such as Aspergillus flavus commonly contaminate animal feeds, causing high economic losses. A. flavus is the most prevalent and produces AFB1, a potent mutagen, and carcinogen threatening human and animal health. Aspergillaceae is a large group of closely related fungi sharing number of morphological and genetic similarities that complicate the diagnosis of highly pathogenic strains. We used here morphological and molecular assays to characterize fungal isolates from animal feeds in Southwestern Algeria. These tools helped to identify 20 out of 30 Aspergillus strains, and 15 of them belonged to the Aspergillus section Flavi. Further analyses detected four out of 15 as belonging to Aspergillus flavus-parasiticus group. PCR targeting the AF genes' aflR-aflS(J) intergenic region amplified a single 674 bp amplicon in all four isolates. The amplicons were digested with a BglII endonuclease, and three specific fragments were observed for A. flavus but A. parasitucus lacked two typical fragments. Sequencing data of four amplicons confirmed the presence of the two BglII restriction sites yielding the three fragments, confirming that all four strains were A. flavus. In addition, this analysis illustrated the genetic variability within the A. flavus strains.

Impact of frequency of application on the long-term efficacy of the biocontrol product Aflasafe in reducing aflatoxin contamination in maize

Aflatoxins, produced by several Aspergillus section Flavi species in various crops, are a significant public health risk and a barrier to trade and development. In sub-Saharan Africa, maize and groundnut are particularly vulnerable to aflatoxin contamination. Aflasafe, a registered aflatoxin biocontrol product, utilizes atoxigenic A. flavus genotypes native to Nigeria to displace aflatoxin producers and mitigate aflatoxin contamination. Aflasafe was evaluated in farmers' fields for 3 years, under various regimens, to quantify carry-over of the biocontrol active ingredient genotypes. Nine maize fields were each treated either continuously for 3 years, the first two successive years, in year 1 and year 3, or once during the first year. For each treated field, a nearby untreated field was monitored. Aflatoxins were quantified in grain at harvest and after simulated poor storage. Biocontrol efficacy and frequencies of the active ingredient genotypes decreased in the absence of annual treatment. Maize treated consecutively for 2 or 3 years had significantly (p < 0.05) less aflatoxin (92% less) in grain at harvest than untreated maize. Maize grain from treated fields subjected to simulated poor storage had significantly less (p < 0.05) aflatoxin than grain from untreated fields, regardless of application regimen. Active ingredients occurred at higher frequencies in soil and grain from treated fields than from untreated fields. The incidence of active ingredients recovered in soil was significantly correlated (r = 0.898; p < 0.001) with the incidence of active ingredients in grain, which in turn was also significantly correlated (r = -0.621, p = 0.02) with aflatoxin concentration. Although there were carry-over effects, caution should be taken when drawing recommendations about discontinuing biocontrol use. Cost-benefit analyses of single season and carry-over influences are needed to optimize use by communities of smallholder farmers in sub-Saharan Africa.

Characterization of the Aspergillus flavus Population from Highly Aflatoxin-Contaminated Corn in the United States

Aflatoxin contamination of corn is a major threat to the safe food and feed. The United States Federal Grain Inspection Service (FGIS) monitors commercial grain shipments for the presence of aflatoxin. A total of 146 Aspergillus flavus were isolated from 29 highly contaminated grain samples to characterize the visual phenotypes, aflatoxin-producing potential, and genotypes to explore the etiological cause of high aflatoxin contamination of US corn. Five of the isolates had reduced sensitivity (43-49% resistant) to the fungicide azoxystrobin, with the remainder all being over 50% resistant to azoxystrobin at the discriminating dose of 2.5 µg/mL. Only six isolates of the highly aflatoxigenic S morphotype were found, and 48 isolates were non-aflatoxigenic. Analysis of the mating type locus revealed 45% MAT 1-1 and 55% MAT 1-2. The A. flavus population originating from the highly aflatoxin contaminated grain samples was compared to a randomly selected subset of isolates originating from commercial corn samples with typical levels of aflatoxin contamination (average < 50 ppb). Use of simple sequence repeat (SSR) genotyping followed by principal component analysis (PCoA) revealed a similar pattern of genotypic distribution in the two populations, but greater diversity in the FGIS-derived population. The noticeable difference between the two populations was that genotypes identical to strain NRRL 21882, the active component of the aflatoxin biocontrol product Afla-Guard™, were ten times more common in the commercial corn population of A. flavus compared to the population from the high-aflatoxin corn samples. The other similarities between the two populations suggest that high aflatoxin concentrations in corn grain are generally the result of infection with common A. flavus genotypes.

Aflatoxin Contamination, Its Impact and Management Strategies: An Updated Review

Aflatoxin, a type of mycotoxin, is mostly produced by Aspergillus flavus and Aspergillus parasiticus. It is responsible for the loss of billions of dollars to the world economy, by contaminating different crops such as cotton, groundnut, maize, and chilies, and causing immense effects on the health of humans and animals. More than eighteen different types of aflatoxins have been reported to date, and among them, aflatoxins B1, B2, G1, and G2 are the most prevalent and lethal. Early detection of fungal infection plays a key role in the control of aflatoxin contamination. Therefore, different methods, including culture, chromatographic techniques, and molecular assays, are used to determine aflatoxin contamination in crops and food products. Many countries have set a maximum limit of aflatoxin contamination (2-20 ppb) in their food and agriculture commodities for human or animal consumption, and the use of different methods to combat this menace is essential. Fungal infection mostly takes place during the pre- and post-harvest stage of crops, and most of the methods to control aflatoxin are employed for the latter phase. Studies have shown that if correct measures are adopted during the crop development phase, aflatoxin contamination can be reduced by a significant level. Currently, the use of bio-pesticides is the intervention employed in many countries, whereby atoxigenic strains competitively reduce the burden of toxigenic strains in the field, thereby helping to mitigate this problem. This updated review on aflatoxins sheds light on the sources of contamination, and the on occurrence, impact, detection techniques, and management strategies, with a special emphasis on bio-pesticides to control aflatoxins.

Characterization of 260 Isolates of Aspergillus Section Flavi Obtained from Sesame Seeds in Punjab, Pakistan

Sesame Sesamum indicum L. is a major oil-based seed crop that has been widely cultivated and consumed in Pakistan. Unfortunately, sesame is highly prone to Aspergillus fungal growth in the field, and under inappropriate storage conditions can become contaminated with aflatoxins, the most potent carcinogen found in nature. Here, we have isolated a high number of Aspergillus isolates from sesame seeds in fresh and stored conditions obtained from rainfed and irrigated zones of Punjab, Pakistan, and characterized them for aflatoxigenic potentials. Using morphological identification techniques, 260 isolates were grouped as potential Aspergillus section Flavi, with 126 and 134 originating from the rainfed and irrigated zones, respectively. Out of 260 in total, 188 isolates were confirmed to produce aflatoxins. There were no significant differences in potential aflatoxigenic isolates with respect to the rainfed and irrigated zones. However, the number of potential aflatoxigenic isolates was significantly higher (p < 0.05) in stored samples than that of those from fresh sesame seeds in the rainfed and irrigated zone. Whole genome sequencing and comparative analyses of 12 select isolates have revealed that one of the A. flavus isolates, which produced very low aflatoxins (AFP10), has an elevated missense variant rate, numerous high impact mutations, and a 600 base pair deletion in the norB gene. In summary, our study provides insights into aflatoxigenic potential and the associated genetic diversity of indigenous Aspergillus section Flavi isolates and potential management strategies for reducing aflatoxin contamination levels in a major crop consumed in Punjab, Pakistan.

Degradation of Aflatoxins B1 by Atoxigenic Aspergillus flavus Biocontrol Agents

Aflatoxins are potent Aspergillus mycotoxins that contaminate food and feed, thereby impacting health and trade. Biopesticides with atoxigenic Aspergillus flavus isolates as active ingredients are used to reduce aflatoxin contamination in crops. The mechanism of aflatoxin biocontrol is primarily attributed to competitive exclusion but, sometimes, aflatoxin is reduced by greater amounts than can be explained by displacement of aflatoxin-producing fungi on the crop. Objectives of this study were to (i) evaluate the ability of atoxigenic A. flavus genotypes to degrade aflatoxin B₁ (AFB1) and (ii) characterize impacts of temperature, time, and nutrient availability on AFB1 degradation by atoxigenic A. flavus. Aflatoxin-contaminated maize was inoculated with atoxigenic isolates in three separate experiments that included different atoxigenic genotypes, temperature, and time as variables. Atoxigenic genotypes varied in aflatoxin degradation but all degraded AFB1 >44% after 7 days at 30°C. The optimum temperature for AFB1 degradation was 25 to 30°C, which is similar to the optimum range for AFB1 production. In a time-course experiment, atoxigenics degraded 40% of AFB1 within 3 days, and 80% of aflatoxin was degraded by day 21. Atoxigenic isolates were able to degrade and utilize AFB1 as a sole carbon source in a chemically defined medium but quantities of AFB1 degraded declined as glucose concentrations increased. Degradation may be an additional mechanism through which atoxigenic A. flavus biocontrol products reduce aflatoxin contamination pre- or postharvest. Thus, selection of optimal atoxigenic active ingredients can include assessment of both competitive ability in agricultural fields and their ability to degrade aflatoxins.

Biocontrol of Aflatoxins Using Non-Aflatoxigenic Aspergillus flavus: A Literature Review

Aflatoxins (AFs) are mycotoxins, predominantly produced by Aspergillus flavus, A. parasiticus, A. nomius, and A. pseudotamarii. AFs are carcinogenic compounds causing liver cancer in humans and animals. Physical and biological factors significantly affect AF production during the pre-and post-harvest time. Several methodologies have been developed to control AF contamination, yet; they are usually expensive and unfriendly to the environment. Consequently, interest in using biocontrol agents has increased, as they are convenient, advanced, and friendly to the environment. Using non-aflatoxigenic strains of A. flavus (AF⁻) as biocontrol agents is the most promising method to control AFs’ contamination in cereal crops. AF⁻ strains cannot produce AFs due to the absence of polyketide synthase genes or genetic mutation. AF⁻ strains competitively exclude the AF⁺ strains in the field, giving an extra advantage to the stored grains. Several microbiological, molecular, and field-based approaches have been used to select a suitable biocontrol agent. The effectiveness of biocontrol agents in controlling AF contamination could reach up to 99.3%. Optimal inoculum rate and a perfect time of application are critical factors influencing the efficacy of biocontrol agents.

Aflasafe SN01 is the First Biocontrol Product Approved for Aflatoxin Mitigation in Two Nations, Senegal and The Gambia

Aflatoxin contamination is caused by Aspergillus flavus and closely related fungi. In The Gambia, aflatoxin contamination of groundnut and maize, two staple and economically important crops, is common. Groundnut and maize consumers are chronically exposed to aflatoxins, sometimes at alarming levels, and this has severe consequences on their health and productivity. Aflatoxin contamination also impedes commercialization in local and international premium markets. In neighboring Senegal, an aflatoxin biocontrol product containing four atoxigenic isolates of A. flavus, Aflasafe SN01, has been registered and is approved for commercial use in groundnut and maize. We detected that the four genotypes composing Aflasafe SN01 are also native to The Gambia. The biocontrol product was tested during two years in 129 maize and groundnut fields and compared with corresponding untreated fields cropped by smallholder farmers in The Gambia. Treated crops contained up to 100% less aflatoxins than untreated crops. A large portion of the crops could have been commercialized in premium markets due to the low aflatoxin content (in many cases no detectable aflatoxins), both at harvest and after storage. Substantial aflatoxin reductions were also achieved when commercially produced groundnut received treatment. Here we report for the first time the use and effectiveness of an aflatoxin biocontrol product registered for use in two nations. With the current scale-out and -up efforts of Aflasafe SN01, a large number of farmers, consumers, and traders in The Gambia and Senegal will obtain health, income, and trade benefits.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Deciphering the origin of Aspergillus flavus NRRL21882, the active biocontrol agent of Afla-Guard®

Single nucleotide polymorphisms (SNPs) of genome sequences of eight Aspergillus flavus and seven Aspergillus oryzae strains were extracted with Mauve, a multiple-genome alignment programme. A phylogenetic analysis with sequences comprised of concatenated total SNPs by the unweighted pair group method with arithmetic mean (UPGMA) of MAFFT adequately separated them into three groups, A. flavus S-morphotype, A. flavus L-morphotype and A. oryzae. Divergence time inferred for A. flavus NRRL21882, the active agent of the biocontrol product Afla-Guard^® , and S-morphotype was about 5·1 mya. Another biocontrol strain, A. flavus AF36, diverged from aflatoxigenic L-morphotype about 2·6-3·0 mya. Despite the close relatedness of A. oryzae to A. flavus, A. oryzae strains likely evolved from aflatoxigenic Aspergillus aflatoxiformans (=A. parvisclerotigenus). A survey of A. flavus populations implies that prior Afla-Guard^® applications are associated with prevalence of NRRL21882-type isolates in Mississippi fields. In addition, a few NRRL21882 relatives were identified. A. flavus Og0222, a biocontrol ingredient of Aflasafe™, was verified as a NRRL21882-type strain, having identical sequence breakpoints that led to deletion of aflatoxin and cyclopiazonic acid gene clusters. A similar UPGMA analysis suggests that the occurrence of NRRL21882-type strains is a more recent event.

Phenotypic Differentiation of Two Morphologically Similar Aflatoxin-Producing Fungi from West Africa

Aflatoxins (AF) are hepatocarcinogenic metabolites produced by several Aspergillus species. Crop infection by these species results in aflatoxin contamination of cereals, nuts, and spices. Etiology of aflatoxin contamination is complicated by mixed infections of multiple species with similar morphology and aflatoxin profiles. The current study investigates variation in aflatoxin production between two morphologically similar species that co-exist in West Africa, A. aflatoxiformans and A. minisclerotigenes. Consistent distinctions in aflatoxin production during liquid fermentation were discovered between these species. The two species produced similar concentrations of AFB₁ in defined media with either urea or ammonium as the sole nitrogen source. However, production of both AFB₁ and AFG₁ were inhibited (p < 0.001) for A. aflatoxiformans in a yeast extract medium with sucrose. Although production of AFG₁ by both species was similar in urea, A. minisclerotigenes produced greater concentrations of AFG₁ in ammonium (p = 0.039). Based on these differences, a reliable and convenient assay for differentiating the two species was designed. This assay will be useful for identifying specific etiologic agents of aflatoxin contamination episodes in West Africa and other regions where the two species are sympatric, especially when phylogenetic analyses based on multiple gene segments are not practical.

Biological Control of Aflatoxin in Maize Grown in Serbia

Aspergillus flavus is the main producer of aflatoxin B1, one of the most toxic contaminants of food and feed. With global warming, climate conditions have become favourable for aflatoxin contamination of agricultural products in several European countries, including Serbia. The infection of maize with A. flavus, and aflatoxin synthesis can be controlled and reduced by application of a biocontrol product based on non-toxigenic strains of A. flavus. Biological control relies on competition between atoxigenic and toxigenic strains. This is the most commonly used biological control mechanism of aflatoxin contamination in maize in countries where aflatoxins pose a significant threat. Mytoolbox Af01, a native atoxigenic A. flavus strain, was obtained from maize grown in Serbia and used to produce a biocontrol product that was applied in irrigated and non-irrigated Serbian fields during 2016 and 2017. The application of this biocontrol product reduced aflatoxin levels in maize kernels (51–83%). The biocontrol treatment had a highly significant effect of reducing total aflatoxin contamination by 73%. This study showed that aflatoxin contamination control in Serbian maize can be achieved through biological control methods using atoxigenic A. flavus strains.

Molecular profile of non-aflatoxigenic phenotype in native strains of Aspergillus flavus

Aflatoxins are the most common mycotoxin contaminant reported in food and feed. Aflatoxin B₁, the most toxic among different aflatoxins, is known to cause hepatocellular carcinoma in animals. Aspergillus flavus and A. parasiticus are the main producers of aflatoxins and are widely distributed in tropical countries. Even though several robust strategies have been in use to control aflatoxin contamination, the control at the pre-harvest level is primitive and incompetent. Therefore, the aim of the study was to isolate and identify the non-aflatoxigenic A. flavus and to delineate the molecular mechanism for the loss of aflatoxin production by the non-aflatoxigenic isolates. Eighteen non-aflatoxigenic strains were isolated from various biological sources using cultural and analytical methods. Among the 18 isolates, 8 isolates produced sclerotia and 17 isolates had type I deletion in norB-cypA region. The isolates were confirmed as A. flavus using gene-specific PCR and sequencing of the ITS region. Later, aflatoxin gene-specific PCR revealed that the defect in one or more genes has led to non-aflatoxigenic phenotype. The strain R9 had maximum defect, and genes avnA and verB had the highest frequency of defect among the non-aflatoxigenic strains. Further, qRT-PCR confirmed that the non-aflatoxigenic strains had high frequency of defect or downregulation in the late pathway genes compared to early pathway genes. Thus, these non-aflatoxigenic strains can be the potential candidates for an effective and proficient strategy for the control of pre-harvest aflatoxin contamination.

"Ground-Truthing" Efficacy of Biological Control for Aflatoxin Mitigation in Farmers' Fields in Nigeria: From Field Trials to Commercial Usage, a 10-Year Study

In sub-Saharan Africa (SSA), diverse fungi belonging to Aspergillus section Flavi frequently contaminate staple crops with aflatoxins. Aflatoxins negatively impact health, income, trade, food security, and development sectors. Aspergillus flavus is the most common causal agent of contamination. However, certain A. flavus genotypes do not produce aflatoxins (i.e., are atoxigenic). An aflatoxin biocontrol technology employing atoxigenic genotypes to limit crop contamination was developed in the United States. The technology was adapted and improved for use in maize and groundnut in SSA under the trademark Aflasafe. Nigeria was the first African nation for which an aflatoxin biocontrol product was developed. The current study includes tests to assess biocontrol performance across Nigeria over the past decade. The presented data on efficacy spans years in which a relatively small number of maize and groundnut fields (8-51 per year) were treated through use on circa 36,000 ha in commercially-produced maize in 2018. During the testing phase (2009-2012), fields treated during one year were not treated in the other years while during commercial usage (2013-2019), many fields were treated in multiple years. This is the first report of a large-scale, long-term efficacy study of any biocontrol product developed to date for a field crop. Most (>95%) of 213,406 tons of maize grains harvested from treated fields contained <20 ppb total aflatoxins, and a significant proportion (>90%) contained <4 ppb total aflatoxins. Grains from treated plots had preponderantly >80% less aflatoxin content than untreated crops. The frequency of the biocontrol active ingredient atoxigenic genotypes in grains from treated fields was significantly higher than in grains from control fields. A higher proportion of grains from treated fields met various aflatoxin standards compared to grains from untreated fields. Results indicate that efficacy of the biocontrol product in limiting aflatoxin contamination is stable regardless of environment and cropping system. In summary, the biocontrol technology allows farmers across Nigeria to produce safer crops for consumption and increases potential for access to premium markets that require aflatoxin-compliant crops.

Detection and Concentration of Plasma Aflatoxin is Associated with Detection of Oncogenic Human Papillomavirus in Kenyan Women

BACKGROUND

Cervical cancer is common in Kenyan women. Cofactors in addition to infection with oncogenic human papillomavirus (HPV) are likely to be important in causing cervical cancer, as only a small percentage of HPV-infected women will develop this malignancy. Kenyan women are exposed to dietary aflatoxin, a potent carcinogen and immunosuppressive agent, which may be such a co-factor.

METHODS

Demographics, behavioral data, plasma, and cervical swabs were collected from 88 HIV-uninfected Kenyan women without cervical dysplasia. HPV detection was compared between women with or without plasma AFB1-lys and evaluated in relation to AFB1-lys concentration.

RESULTS

Valid HPV testing results were available for 86 women (mean age 34.0 years); 49 women (57.0%) had AFB1-lys detected and 37 (43.0%) had none. AFB1-lys detection was not associated with age, being married, having more than secondary school education, home ownership, living at a walking distance to health care ≥60 minutes, number of lifetime sex partners, or age of first sex. AFB1-lys detection and plasma concentrations were associated with detection of oncogenic HPV types.

CONCLUSIONS

AFB1-lys-positivity and higher plasma AFB1-lys concentrations were associated with higher risk of oncogenic HPV detection in cervical samples from Kenya women. Further studies are needed to determine if aflatoxin interacts with HPV in a synergistic manner to increase the risk of cervical cancer.

Whole genome comparison of Aspergillus flavus L-morphotype strain NRRL 3357 (type) and S-morphotype strain AF70

Aspergillus flavus is a saprophytic fungus that infects corn, peanuts, tree nuts and other agriculturally important crops. Once the crop is infected the fungus has the potential to secrete one or more mycotoxins, the most carcinogenic of which is aflatoxin. Aflatoxin contaminated crops are deemed unfit for human or animal consumption, which results in both food and economic losses. Within A. flavus, two morphotypes exist: the S strains (small sclerotia) and L strains (large sclerotia). Significant morphological and physiological differences exist between the two morphotypes. For example, the S-morphotypes produces sclerotia that are smaller (< 400 μm), greater in quantity, and contain higher concentrations of aflatoxin than the L-morphotypes (>400 μm). The morphotypes also differ in pigmentation, pH homeostasis in culture and the number of spores produced. Here we report the first full genome sequence of an A. flavus S morphotype, strain AF70. We provide a comprehensive comparison of the A. flavus S-morphotype genome sequence with a previously sequenced genome of an L-morphotype strain (NRRL 3357), including an in-depth analysis of secondary metabolic clusters and the identification SNPs within their aflatoxin gene clusters.

Characterization of Argentinian Endemic Aspergillus flavus Isolates and Their Potential Use as Biocontrol Agents for Mycotoxins in Maize

Maize (Zea mays L.) is a highly valuable crop in Argentina, frequently contaminated with the mycotoxins produced by Aspergillus flavus. Biocontrol products formulated with atoxigenic (nontoxic) strains of this fungal species are well known as an effective method to reduce this contamination. In the present study, 83 A. flavus isolates from two maize regions of Argentina were characterized and evaluated for their ability to produce or lack of producing mycotoxins in order to select atoxigenic strains to be used as potential biocontrol agents (BCA). All of the isolates were tested for aflatoxin and cyclopiazonic acid (CPA) production in maize kernels and a liquid culture medium. Genetic diversity of the nonaflatoxigenic isolates was evaluated by analysis of vegetative compatibility groups (VCG) and confirmation of deletions in the aflatoxin biosynthesis cluster. Eight atoxigenic isolates were compared for their ability to reduce aflatoxin and CPA contamination in maize kernels in coinoculation tests. The A. flavus population was composed of 32% aflatoxin and CPA producers and 52% CPA producers, and 16% was determined as atoxigenic. All of the aflatoxin producer isolates also produced CPA. Aflatoxin and CPA production was significantly higher in maize kernels than in liquid medium. The 57 nonaflatoxigenic strains formed six VCG, with AM1 and AM5 being the dominant groups, with a frequency of 58 and 35%, respectively. In coinoculation experiments, all of the atoxigenic strains reduced aflatoxin from 54 to 83% and CPA from 60 to 97%. Members of group AM1 showed a greater aflatoxin reduction than members of AM5 (72 versus 66%) but no differences were detected in CPA production. Here, we described for the first time atoxigenic isolates of A. flavus that show promise to be used as BCA in maize crops in Argentina. This innovating biological control approach should be considered, developed further, and used by the maize industry to preserve the quality properties and food safety of maize kernels in Argentina.

Metabolites Identified during Varied Doses of Aspergillus Species in Zea mays Grains, and Their Correlation with Aflatoxin Levels

Aflatoxin contamination is associated with the development of aflatoxigenic fungi such as Aspergillus flavus and A. parasiticus on food grains. This study was aimed at investigating metabolites produced during fungal development on maize and their correlation with aflatoxin levels. Maize cobs were harvested at R3 (milk), R4 (dough), and R5 (dent) stages of maturity. Individual kernels were inoculated in petri dishes with four doses of fungal spores. Fungal colonisation, metabolite profile, and aflatoxin levels were examined. Grain colonisation decreased with kernel maturity: milk-, dough-, and dent-stage kernels by approximately 100%, 60%, and 30% respectively. Aflatoxin levels increased with dose at dough and dent stages. Polar metabolites including alanine, proline, serine, valine, inositol, iso-leucine, sucrose, fructose, trehalose, turanose, mannitol, glycerol, arabitol, inositol, myo-inositol, and some intermediates of the tricarboxylic acid cycle (TCA&mdash;also known as citric acid or Krebs cycle) were important for dose classification. Important non-polar metabolites included arachidic, palmitic, stearic, 3,4-xylylic, and margaric acids. Aflatoxin levels correlated with levels of several polar metabolites. The strongest positive and negative correlations were with arabitol (R = 0.48) and turanose and (R = &minus;0.53), respectively. Several metabolites were interconnected with the TCA; interconnections of the metabolites with the TCA cycle varied depending upon the grain maturity.

Prevalence of Aflatoxin Contamination in Maize and Groundnut in Ghana: Population Structure, Distribution, and Toxigenicity of the Causal Agents

Aflatoxin contamination in maize and groundnut is perennial in Ghana with substantial health and economic burden on the population. The present study examined for the first time the prevalence of aflatoxin contamination in maize and groundnut in major producing regions across three agroecological zones (AEZs) in Ghana. Furthermore, the distribution and aflatoxin-producing potential of Aspergillus species associated with both crops were studied. Out of 509 samples (326 of maize and 183 of groundnut), 35% had detectable levels of aflatoxins. Over 15% of maize and 11% of groundnut samples exceeded the aflatoxin threshold limits set by the Ghana Standards Authority of 15 and 20 ppb, respectively. Mycoflora analyses revealed various species and morphotypes within the Aspergillus section Flavi. A total of 5,083 isolates were recovered from both crops. The L morphotype of Aspergillus flavus dominated communities with 93.3% of the population, followed by Aspergillus spp. with S morphotype (6%), A. tamarii (0.4%), and A. parasiticus (0.3%). Within the L morphotype, the proportion of toxigenic members was significantly (P < 0.05) higher than that of atoxigenic members across AEZs. Observed and potential aflatoxin concentrations indicate that on-field aflatoxin management strategies need to be implemented throughout Ghana. The recovered atoxigenic L morphotype fungi are genetic resources that can be employed as biocontrol agents to limit aflatoxin contamination of maize and groundnut in Ghana. Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Advances in molecular and genomic research to safeguard food and feed supply from aflatoxin contamination

Worldwide recognition that aflatoxin contamination of agricultural commodities by the fungus Aspergillus flavus is a global problem has significantly benefitted from global collaboration for understanding the contaminating fungus, as well as for developing and implementing solutions against the contamination. The effort to address this serious food and feed safety issue has led to a detailed understanding of the taxonomy, ecology, physiology, genomics and evolution of A. flavus, as well as strategies to reduce or control pre-harvest aflatoxin contamination, including (1) biological control, using atoxigenic aspergilli, (2) proteomic and genomic analyses for identifying resistance factors in maize as potential breeding markers to enable development of resistant maize lines, and (3) enhancing host-resistance by bioengineering of susceptible crops, such as cotton, maize, peanut and tree nuts. A post-harvest measure to prevent the occurrence of aflatoxin contamination in storage is also an important component for reducing exposure of populations worldwide to aflatoxins in food and feed supplies. The effect of environmental changes on aflatoxin contamination levels has recently become an important aspect for study to anticipate future contamination levels. The ability of A. flavus to produce dozens of secondary metabolites, in addition to aflatoxins, has created a new avenue of research for understanding the role these metabolites play in the survival and biodiversity of this fungus. The understanding of A. flavus, the aflatoxin contamination problem, and control measures to prevent the contamination has become a unique example for an integrated approach to safeguard global food and feed safety.

Isolation and characterization of Aspergillus flavus strains in China

Important staple foods (peanuts, maize and rice) are susceptible to contamination by aflatoxin (AF)-producing fungi such as Aspergillus flavus. The objective of this study was to explore non-aflatoxin-producing (atoxigenic) A. flavus strains as biocontrol agents for the control of AFs. In the current study, a total of 724 A. flavus strains were isolated from different regions of China. Polyphasic approaches were utilized for species identification. Non-aflatoxin and non-cyclopiazonic acid (CPA)-producing strains were further screened for aflatoxin B₁ (AFB₁) biosynthesis pathway gene clusters using a PCR assay. Strains lacking an amplicon for the regulatory gene aflR were then analyzed for the presence of the other 28 biosynthetic genes. Only 229 (32%) of the A. flavus strains were found to be atoxigenic. Smaller (S) sclerotial phenotypes were dominant (51%) compared to large (L, 34%) and non-sclerotial (NS, 15%) phenotypes. Among the atoxigenic strains, 24 strains were PCR-negative for the fas-1 and aflJ genes. Sixteen (67%) atoxigenic A. flavus strains were PCRnegative for 10 or more of the biosynthetic genes. Altogether, 18 new PCR product patterns were observed, indicating great diversity in the AFB₁ biosynthesis pathway. The current study demonstrates that many atoxigenic A. flavus strains can be isolated from different regions of China. In the future laboratory as well as field based studies are recommended to test these atoxigenic strains as biocontrol agents for aflatoxin contamination.

Carbon Dioxide Mediates the Response to Temperature and Water Activity Levels in Aspergillus flavus during Infection of Maize Kernels

Aspergillus flavus is a saprophytic fungus that may colonize several important crops, including cotton, maize, peanuts and tree nuts. Concomitant with A. flavus colonization is its potential to secrete mycotoxins, of which the most prominent is aflatoxin. Temperature, water activity (aw) and carbon dioxide (CO₂) are three environmental factors shown to influence the fungus-plant interaction, which are predicted to undergo significant changes in the next century. In this study, we used RNA sequencing to better understand the transcriptomic response of the fungus to aw, temperature, and elevated CO₂ levels. We demonstrate that aflatoxin (AFB₁) production on maize grain was altered by water availability, temperature and CO₂. RNA-Sequencing data indicated that several genes, and in particular those involved in the biosynthesis of secondary metabolites, exhibit different responses to water availability or temperature stress depending on the atmospheric CO₂ content. Other gene categories affected by CO₂ levels alone (350 ppm vs. 1000 ppm at 30 °C/0.99 aw), included amino acid metabolism and folate biosynthesis. Finally, we identified two gene networks significantly influenced by changes in CO₂ levels that contain several genes related to cellular replication and transcription. These results demonstrate that changes in atmospheric CO₂ under climate change scenarios greatly influences the response of A. flavus to water and temperature when colonizing maize grain.

Vegetative compatibility and phenotypic characterization as a means of determining genetic diversity of Aspergillus flavus isolates

Toxigenic Aspergillus species produce mycotoxins that are carcinogenic, hepatotoxic and teratogenic immunosuppressing agents in both human and animals. Kenya frequently experiences outbreaks of aflatoxicosis with the worst occurring in 2010, which resulted in 215 deaths. We examined the possible reasons for these frequent aflatoxicosis outbreaks in Kenya by studying Aspergillus flavus diversity, phenotypes and mycotoxin profiles across various agricultural regions. Using diagonal transect random sampling, maize kernels were collected from Makueni, Homa Bay, Nandi, and Kisumu counties. Out of 37 isolates, nitrate non-utilizing auxotrophs complementation test revealed 20 vegetative compatibility groups. We designated these groups by the prefix "KVCG", where "K" represented Kenya and consequently assigned numbers 1-20 based on our findings. KVCG14 and KVCG15 had highest distribution frequency (n = 13; 10.8 %). The distribution of the L-, S- and S-/L-morphotypes across the regions were 57 % (n = 21); 7 % (n = 3) and 36 % (n = 13), respectively. Furthermore, a unique isolate (KSM015) was identified that had characteristics of S-morphotype, but produced both aflatoxins B and G. Coconut agar medium (CAM) assay, TLC and HPLC analyses confirmed the presence or absence of aflatoxins in selected toxigenic and atoxigenic isolates. Diversity index (H') analyses ranged from 0.11 (Nandi samples) to 0.32 (Kisumu samples). Heterokaryon compatibility ranged from 33 % (for the Makueni samples, n = 3) to 67 % (Nandi samples, n = 6). To our knowledge, this is the first reported findings for A. flavus diversity and distribution in Nandi, Homa Bay and Kisumu counties and may assist current and future researchers in the selection of biocontrol strategies to mitigate aflatoxin contamination as has been researched in Makueni and neighbouring counties.

Distribution and incidence of atoxigenic Aspergillus flavus VCG in tree crop orchards in California: A strategy for identifying potential antagonists, the example of almonds

To identify predominant isolates for potential use as biocontrol agents, Aspergillus flavus isolates collected from soils of almond, pistachio and fig orchard in the Central Valley of California were tested for their membership to 16 atoxigenic vegetative compatibility groups (VCGs), including YV36, the VCG to which AF36, an atoxigenic isolate commercialized in the United States as biopesticide, belongs. A surprisingly large proportion of isolates belonged to YV36 (13.3%, 7.2% and 6.6% of the total almond, pistachio and fig populations, respectively), while the percentage of isolates belonging to the other 15 VCGs ranged from 0% to 2.3%. In order to gain a better insight into the structure and diversity of atoxigenic A. flavus populations and to further identify predominant isolates, seventeen SSR markers were then used to genetically characterize AF36, the 15 type-isolates of the VCGs and 342 atoxigenic isolates of the almond population. There was considerable genetic diversity among isolates with a lack of differentiation among micro-geographical regions or years. Since isolates sharing identical SSR profiles from distinct orchards were rare, we separated them into groups of at least 3 closely-related isolates from distinct orchards that shared identical alleles for at least 15 out of the 17 loci. This led to the identification of 15 groups comprising up to 24 closely-related isolates. The group which contained the largest number of isolates were members of YV36 while five groups were also found to be members of our studied atoxigenic VCGs. These results suggest that these 15 groups, and AF36 in particular, are well adapted to various environmental conditions in California and to tree crops and, as such, are good candidates for use as biocontrol agents.

Biological control of aflatoxins in Africa: current status and potential challenges in the face of climate change

Aflatoxin contamination of crops is frequent in warm regions across the globe, including large areas in sub-Saharan Africa. Crop contamination with these dangerous toxins transcends health, food security, and trade sectors. It cuts across the value chain, affecting farmers, traders, markets, and finally consumers. Diverse fungi within Aspergillus section Flavi contaminate crops with aflatoxins. Within these Aspergillus communities, several genotypes are not capable of producing aflatoxins (atoxigenic). Carefully selected atoxigenic genotypes in biological control (biocontrol) formulations efficiently reduce aflatoxin contamination of crops when applied prior to flowering in the field. This safe and environmentally friendly, effective technology was pioneered in the US, where well over a million acres of susceptible crops are treated annually. The technology has been improved for use in sub-Saharan Africa, where efforts are under way to develop biocontrol products, under the trade name Aflasafe, for 11 African nations. The number of participating nations is expected to increase. In parallel, state of the art technology has been developed for large-scale inexpensive manufacture of Aflasafe products under the conditions present in many African nations. Results to date indicate that all Aflasafe products, registered and under experimental use, reduce aflatoxin concentrations in treated crops by >80% in comparison to untreated crops in both field and storage conditions. Benefits of aflatoxin biocontrol technologies are discussed along with potential challenges, including climate change, likely to be faced during the scaling-up of Aflasafe products. Lastly, we respond to several apprehensions expressed in the literature about the use of atoxigenic genotypes in biocontrol formulations. These responses relate to the following apprehensions: sorghum as carrier, distribution costs, aflatoxin-conscious markets, efficacy during drought, post-harvest benefits, risk of allergies and/or aspergillosis, influence of Aflasafe on other mycotoxins and on soil microenvironment, dynamics of Aspergillus genotypes, and recombination between atoxigenic and toxigenic genotypes in natural conditions.

Degeneration of aflatoxin gene clusters in Aspergillus flavus from Africa and North America

Aspergillus flavus is the most common causal agent of aflatoxin contamination of food and feed. However, aflatoxin-producing potential varies widely among A. flavus genotypes with many producing no aflatoxins. Some non-aflatoxigenic genotypes are used as biocontrol agents to prevent contamination. Aflatoxin biosynthesis genes are tightly clustered in a highly conserved order. Gene deletions and presence of single nucleotide polymorphisms (SNPs) in aflatoxin biosynthesis genes are often associated with A. flavus inability to produce aflatoxins. In order to identify mechanisms of non-aflatoxigenicity in non-aflatoxigenic genotypes of value in aflatoxin biocontrol, complete cluster sequences of 35 A. flavus genotypes from Africa and North America were analyzed. Inability of some genotypes to produce aflatoxin resulted from deletion of biosynthesis genes. In other genotypes, non-aflatoxigenicity originated from SNP formation. The process of degeneration differed across the gene cluster; genes involved in early biosynthesis stages were more likely to be deleted while genes involved in later stages displayed high frequencies of SNPs. Comparative analyses of aflatoxin gene clusters provides insight into the diversity of mechanisms of non-aflatoxigenicity in A. flavus genotypes used as biological control agents. The sequences provide resources for both diagnosis of non-aflatoxigenicity and monitoring of biocontrol genotypes during biopesticide manufacture and in the environment.

Environmental distribution and genetic diversity of vegetative compatibility groups determine biocontrol strategies to mitigate aflatoxin contamination of maize by Aspergillus flavus

Maize infected by aflatoxin-producing Aspergillus flavus may become contaminated with aflatoxins, and as a result, threaten human health, food security and farmers' income in developing countries where maize is a staple. Environmental distribution and genetic diversity of A. flavus can influence the effectiveness of atoxigenic isolates in mitigating aflatoxin contamination. However, such information has not been used to facilitate selection and deployment of atoxigenic isolates. A total of 35 isolates of A. flavus isolated from maize samples collected from three agro-ecological zones of Nigeria were used in this study. Ecophysiological characteristics, distribution and genetic diversity of the isolates were determined to identify vegetative compatibility groups (VCGs). The generated data were used to inform selection and deployment of native atoxigenic isolates to mitigate aflatoxin contamination in maize. In co-inoculation with toxigenic isolates, atoxigenic isolates reduced aflatoxin contamination in grain by > 96%. A total of 25 VCGs were inferred from the collected isolates based on complementation tests involving nitrate non-utilizing (nit(-)) mutants. To determine genetic diversity and distribution of VCGs across agro-ecological zones, 832 nit(-) mutants from 52 locations in 11 administrative districts were paired with one self-complementary nitrate auxotroph tester-pair for each VCG. Atoxigenic VCGs accounted for 81.1% of the 153 positive complementations recorded. Genetic diversity of VCGs was highest in the derived savannah agro-ecological zone (H = 2.61) compared with the southern Guinea savannah (H = 1.90) and northern Guinea savannah (H = 0.94) zones. Genetic richness (H = 2.60) and evenness (E5  = 0.96) of VCGs were high across all agro-ecological zones. Ten VCGs (40%) had members restricted to the original location of isolation, whereas 15 VCGs (60%) had members located between the original source of isolation and a distance > 400 km away. The present study identified widely distributed VCGs in Nigeria such as AV0222, AV3279, AV3304 and AV16127, whose atoxigenic members can be deployed for a region-wide biocontrol of toxigenic isolates to reduce aflatoxin contamination in maize.

Genetic Analysis of the Aspergillus flavus Vegetative Compatibility Group to Which a Biological Control Agent That Limits Aflatoxin Contamination in U.S. Crops Belongs

Some filamentous fungi in Aspergillus section Flavi produce carcinogenic secondary compounds called aflatoxins. Aflatoxin contamination is routinely managed in commercial agriculture with strains of Aspergillus flavus that do not produce aflatoxins. These non-aflatoxin-producing strains competitively exclude aflatoxin producers and reshape fungal communities so that strains with the aflatoxin-producing phenotype are less frequent. This study evaluated the genetic variation within naturally occurring atoxigenic A. flavus strains from the endemic vegetative compatibility group (VCG) YV36. AF36 is a strain of VCG YV36 and was the first fungus used in agriculture for aflatoxin management. Genetic analyses based on mating-type loci, 21 microsatellite loci, and a single nucleotide polymorphism (SNP) in the aflC gene were applied to a set of 237 YV36 isolates collected from 1990 through 2005 from desert legumes and untreated fields and from fields previously treated with AF36 across the southern United States. One haplotype dominated across time and space. No recombination with strains belonging to VCGs other than YV36 was detected. All YV36 isolates carried the SNP in aflC that prevents aflatoxin biosynthesis and the mat1-2 idiomorph at the mating-type locus. These results suggest that VCG YV36 has a clonal population structure maintained across both time and space. These results demonstrate the genetic stability of atoxigenic strains belonging to a broadly distributed endemic VCG in both untreated populations and populations where the short-term frequency of VCG YV36 has increased due to applications of a strain used to competitively exclude aflatoxin producers. This work supports the hypothesis that strains of this VCG are not involved in routine genetic exchange with aflatoxin-producing strains.

Comparative data concerning aflatoxin contents in Bt maize and non-Bt isogenic maize in relation to human and animal health – a review

Transgenic Bt maize is a potentially important tool against insect pest in the EU and other countries. Bt maize (e.g. MON 810, Bt 11) which carries the Bt gene is highly resistant to larval feeding of European corn borer, stalk borer, and Southwestern corn borer, depending on Bt toxin (δ toxin) production. Effective measures used to fight pests may often have positive side-effects in that they may also contribute to reducing mycotoxin concentrations. A systematic review has been used for the purposes of evaluating the studies on the reduction of aflatoxins in Bt maize. According to five studies, Bt maize has significantly lower concentrations of aflatoxins than non-Bt maize hybrids, only one study has shown no significant effect of Bt maize. Other studies have shown mixed results (four studies). The results of these studies were influenced by the year of sampling or by using maize breeding lines selected for resistance to aflatoxin accumulation.

High sequence variations in the region containing genes encoding a cellular morphogenesis protein and the repressor of sexual development help to reveal origins of Aspergillus oryzae

Aspergillus oryzae and Aspergillus flavus are closely related fungal species. The A. flavus morphotype that produces numerous small sclerotia (S strain) and aflatoxin has a unique 1.5 kb deletion in the norB-cypA region of the aflatoxin gene cluster (i.e. the S genotype). Phylogenetic studies have indicated that an isolate of the nonaflatoxigenic A. flavus with the S genotype is the ancestor of A. oryzae. Genome sequence comparison between A. flavus NRRL3357, which produces large sclerotia (L strain), and S-strain A. flavus 70S identified a region (samA-rosA) that was highly variable in the two morphotypes. A third type of samA-rosA region was found in A. oryzae RIB40. The three samA-rosA types were later revealed to be commonly present in A. flavus L-strain populations. Of the 182 L-strain A. flavus field isolates examined, 46%, 15% and 39% had the samA-rosA type of NRRL3357, 70S and RIB40, respectively. The three types also were found in 18 S-strain A. flavus isolates with different proportions. For A. oryzae, however, the majority (80%) of the 16 strains examined had the RIB40 type and none had the NRRL3357 type. The results suggested that A. oryzae strains in the current culture collections were mostly derived from the samA-rosA/RIB40 lineage of the nonaflatoxigenic A. flavus with the S genotype.

Method for monitoring deletions in the aflatoxin biosynthesis gene cluster of Aspergillus flavus with multiplex PCR

The report presents a rapid, inexpensive and simple method for monitoring indels with influence on aflatoxin biosynthesis within Aspergillus flavus populations. PCR primers were developed for 32 markers spaced approximately every 5 kb from 20 kb proximal to the aflatoxin biosynthesis gene cluster to the telomere repeat. This region includes gene clusters required for biosynthesis of aflatoxins and cyclopiazonic acid; the resulting data were named cluster amplification patterns (CAPs). CAP markers are amplified in four multiplex PCRs, greatly reducing the cost and time to monitor indels within this region across populations. The method also provides a practical tool for characterizing intraspecific variability in A. flavus not captured with other methods.

SIGNIFICANCE AND IMPACT OF THE STUDY

Aflatoxins, potent naturally-occurring carcinogens, cause significant agricultural problems. The most effective method for preventing contamination of crops with aflatoxins is through use of atoxigenic strains of Aspergillus flavus to alter the population structure of this species and reduce incidences of aflatoxin producers. Cluster amplification pattern (CAP) is a rapid multiplex PCR method for identifying and monitoring indels associated with atoxigenicity in A. flavus. Compared to previous techniques, the reported method allows for increased resolution, reduced cost, and greater speed in monitoring the stability of atoxigenic strains, incidences of indel mediated atoxigenicity and the structure of A. flavus populations.

Genetic variability of Aspergillus flavus isolates from a Mississippi corn field

A nontoxigenic Aspergillus flavus strain, K49, is currently being tested as a biological control agent in corn fields in the Mississippi Delta. However, little is known about the overall genetic diversity of A. flavus from year to year in corn fields and specifically in Mississippi. Our objective was to assess the genetic variability of A. flavus isolates from different seasons, inoculum sources, and years, from a no-till corn field. Of the 175 A. flavus isolates examined, 74 and 97 had the typical norB-cypA type I (1.5 kb) and type II (1.0 kb) deletion patterns, respectively. Variability in the sequence of the omtA gene of the majority of the field isolates (n = 118) was compared to strain K49. High levels of haplotypic diversity (24 omtA haplotypes; Hd = 0.61 ± 0.04) were found. Among the 24 haplotypes, two were predominant, H1 (n = 71), which consists of mostly toxigenic isolates, and H49 (n = 18), which consists of mostly atoxigenic isolates including K49. Toxigenic isolates were prevalent (60%) in this natural population. Nonetheless, about 15% of the population likely shared the same ancestral origin with K49. This study provides valuable information on the diversity of A. flavus. This knowledge can be further used to develop additional biological control strains.

Biodiversity of Aspergillus section Flavi in Europe in relation to the management of aflatoxin risk

Aflatoxins and the producing fungi Aspergillus section Flavi are widely known as the most serious and dangerous mycotoxin issue in agricultural products. In Europe, before the outbreak of aflatoxins on maize (2003-2004) due to new climatic conditions, their contamination was confined to imported foods. Little information is available on molecular biodiversity and population structure of Aspergillus section Flavi in Europe. Preliminary reports evidenced the massive presence of Aspergillus flavus L -morphotype as the predominant species in maize field, no evidence of the highly toxigenic S-morphotype and of other aflatoxigenic species are reported. The risk of a shift in traditional occurrence areas for aflatoxins is expected in the world and in particular in South East of Europe due to the increasing average temperatures. Biological control of aflatoxin risk in the field by atoxigenic strains of A. flavus starts to be widely used in Africa and USA. Studies are necessary on the variation of aflatoxin production in populations of A. flavus to characterize stable atoxigenic A. flavus strains. The aim of present article is to give an overview on biodiversity and genetic variation of Aspergillus section Flavi in Europe in relation to the management of aflatoxins risk in the field.

Population structure and aflatoxin production by Aspergillus Sect. Flavi from maize in Nigeria and Ghana

Aflatoxins are highly toxic carcinogens that contaminate crops worldwide. Previous studies conducted in Nigeria and Ghana found high concentrations of aflatoxins in pre- and post-harvest maize. However, little information is available on the population structure of Aspergillus Sect. Flavi in West Africa. We determined the incidence of Aspergillus Sect. Flavi and the level of aflatoxin contamination in 91 maize samples from farms and markets in Nigeria and Ghana. Aspergillus spp. were recovered from 61/91 maize samples and aflatoxins B1 and/or B2 occurred in 36/91 samples. Three samples from the farms also contained aflatoxin G1 and/or G2. Farm samples were more highly contaminated than were samples from the market, in terms of both the percentage of the samples contaminated and the level of mycotoxin contamination. One-hundred-and-thirty-five strains representative of the 1163 strains collected were identified by using a multilocus sequence analysis of portions of the genes encoding calmodulin, β-tubulin and actin, and evaluated for aflatoxin production. Of the 135 strains, there were 110 - Aspergillus flavus, 20 - Aspergillus tamarii, 2 - Aspergillus wentii, 2 - Aspergillus flavofurcatus, and 1 - Aspergillus parvisclerotigenus. Twenty-five of the A. flavus strains and the A. parvisclerotigenus strain were the only strains that produced aflatoxins. The higher contamination of the farm than the market samples suggests that the aflatoxin exposure of rural farmers is even higher than previously estimated based on reported contamination of market samples. The relative infrequency of the A. flavus SBG strains, producing small sclerotia and high levels of both aflatoxins (B and G), suggests that long-term chronic exposure to this mycotoxin are a much higher health risk in West Africa than is the acute toxicity due to very highly contaminated maize in east Africa.

Multiplex PCR analysis of fumonisin biosynthetic genes in fumonisin-nonproducing Aspergillus niger and A. awamori strains

To determine the genetic basis for loss of fumonisin B2 (FB2) biosynthesis in FB2-nonproducing Aspergillus niger and A. awamori strains, we developed multiplex PCR primer sets to amplify fragments of eight fumonisin biosynthetic pathway (fum) genes. Fragments of all eight fum genes were amplified from FB2-producing A. niger and A. awamori strains; from FB2-nonproducing strains four amplification patterns arose in which one or more fum gene fragments were absent. Southern hybridization analysis of strains yielding patterns 2 and 3 confirmed that loss of FB2 production in A. awamori is associated with gene deletions within the fumonisin biosynthetic gene cluster. In addition, we observed a fifth multiplex amplification pattern in which all eight fum gene fragments appeared. Reverse transcription-PCR analysis of strains yielding pattern 5 showed that the expression of at least one fum gene was reduced relative to expression in FB2-producing A. niger. This suggests that in these strains loss of FB2 production is a result of structural or regulatory mutations that alter gene expression or function. These results demonstrate a diversity of genotypes within FB2-nonproducing A. niger and A. awamori populations and provide tools useful for identifying certain non-toxigenic strains for industrial or ecological applications.

Identification of Atoxigenic Aspergillus flavus Isolates to Reduce Aflatoxin Contamination of Maize in Kenya

Aspergillus flavus has two morphotypes, the S strain and the L strain, that differ in aflatoxin-producing ability and other characteristics. Fungal communities on maize dominated by the S strain of A. flavus have repeatedly been associated with acute aflatoxin poisonings in Kenya, where management tools to reduce aflatoxin levels in maize are needed urgently. A. flavus isolates (n = 290) originating from maize produced in Kenya and belonging to the L strain morphotype were tested for aflatoxin-producing potential. A total of 96 atoxigenic isolates was identified from four provinces sampled. The 96 atoxigenic isolates were placed into 53 vegetative compatibility groups (VCGs) through complementation of nitrate non-utilizing mutants. Isolates from each of 11 VCGs were obtained from more than one maize sample, isolates from 10 of the VCGs were detected in multiple districts, and isolates of four VCGs were found in multiple provinces. Atoxigenic isolates were tested for potential to reduce aflatoxin concentrations in viable maize kernels that were co-inoculated with highly toxigenic S strain isolates. The 12 most effective isolates reduced aflatoxin levels by >80%. Reductions in aflatoxin levels caused by the most effective Kenyan isolates were comparable with those achieved with a United States isolate (NRRL-21882) used commercially for aflatoxin management. This study identified atoxigenic isolates of A. flavus with potential value for biological control within highly toxic Aspergillus communities associated with maize production in Kenya. These atoxigenic isolates have potential value in mitigating aflatoxin outbreaks in Kenya, and should be evaluated under field conditions.