Non-aflatoxigenic Aspergillus Flavus Research Articles

Telomere-to-telomere genome assembly of the aflatoxin biocontrol agent Aspergillus flavus isolate La3279 isolated from maize in Nigeria.

Here, we report the complete genome of the non-aflatoxigenic Aspergillus flavus isolate La3279, which is an active ingredient of the aflatoxin biocontrol product Aflasafe. The chromosome-scale assembly clarifies the deletion pattern in the aflatoxin biosynthesis gene cluster and corrects a misidentified assembly previously published for this isolate.

Microbiota of maize kernels as influenced by Aspergillus flavus infection in susceptible and resistant inbreds.

Nearly everything on Earth harbors a microbiome. A microbiome is a community of microbes (bacteria, fungi, and viruses) with potential to form complex networks that involve mutualistic and antagonistic interactions. Resident microbiota on/in an organism are determined by the external environment, both biotic and abiotic, and the intrinsic adaptability of each organism. Although the maize microbiome has been characterized, community changes that result from the application of fungal biocontrol strains, such as non-aflatoxigenic Aspergillus flavus, have not. We silk channel inoculated field-grown maize separately with a non-aflatoxigenic biocontrol strain (K49), a highly toxigenic strain (Tox4), and a combination of both A. flavus strains. Two maize inbreds were treated, A. flavus-susceptible B73 and A. flavus-resistant CML322. We then assessed the impacts of A. flavus introduction on the epibiota and endobiota of their maize kernels. We found that the native microbial communities were significantly affected, irrespective of genotype or sampled tissue. Overall, bacteriomes exhibited greater diversity of genera than mycobiomes. The abundance of certain genera was unchanged by treatment, including genera of bacteria (e.g., Enterobacter, Pantoea) and fungi (e.g., Sarocladium, Meyerozyma) that are known to be beneficial, antagonistic, or both on plant growth and health. Beneficial microbes like Sarocladium that responded well to A. flavus biocontrol strains are expected to enhance biocontrol efficacy, while also displacing/antagonizing harmful microbes.

Molecular characterization of aflatoxigenic and non-aflatoxigenic Aspergillus flavus strains isolated from peanut sold in northern Togo

The contamination of agricultural products and aflatoxins synthesis can be controlled and reduced by the application of a biological control product based on atoxinogenic Aspergillus flavus strains. The purpose of this work was to select atoxinogenic Aspergillus flavus strains that can be used in the biological control of aflatoxins. Thirty-four (34) strains of Aspergillus flavus were used and the Nor-1, Ver-1, Omt-A and AflR genes involved in the aflatoxin biosynthesis pathway were sought. The growth speed and ability of atoxigenic strains to inhibit the growth of toxigenic strains were also determined. The results showed that 50% of the strains have at least one of the genes sought and the percentages of inhibition (PI) of the atoxinogenic strains varied significantly from 16.98% to 62.50% at the threshold of 5% according to the Tukey test (p-value = 0.0000136). The mycelial growth speed (VCM) of the atoxinogenic strains varied from 7.5 to 10 mm/day with an average VCM of 8.4 ± 0.05 mm/day. Strains AKA-10; AGA-8; AMAN-35; ABA-28 and AGA-46 were found to be more effective in inhibiting mycelial growth of toxigenic strains.

Characterization and Determination of Aflatoxigenic and Non-aflatoxigenic Aspergillus flavus Isolated from Bakery Food Products from Frontier around Davangere District

Mycotoxins are secondary metabolites produced by filamentous fungi in food and feed due to several conditions that affect fungal growth and mycotoxin production in different ways. Mycotoxin contamination in bakery food products is seriously dangerous to humans and animals. This study aimed to morphologically characterize and determine the aflatoxigenic and non-aflatoxigenic Aspergillus flavus isolates. Thirty three isolates of A.flavus were obtained from bakery food products collected from bakeries in rural areas like Bathi, Kodaganur, Bada, sasalu, Mayakonda, Avargere, Anaberu, Alur, Attigere, Echagatta around Davangere city. They were cultured on Potato Dextrose Agar medium (PDA), Rose Bengal Agar medium (RBA), Czapec(dox) agar medium (CZA) and Sabouraud’s dextrose agar medium (SDA). By observing the colony color and texture macromorphological characteristics were determined and micromorphological characteristics were determined by observing the spore color, size, structure, conidiophore structure, conidia, vesical shape under microscope. The production of aflatoxin was determined by UV fluorescence of isolates on coconut cream agar (CCA) medium plates. In aflatoxin detection 20 (60.60%) isolates of A.flavus shows positive results and 13 (39.39%) isolates of A.flavus shows negative results. The highest incidence of A.flavus was recorded in samples collected from Attigere followed by Bathi, Alur, Echagatta, Kodaganur, Bada, Anaberu, Sasalu, Mayakonda, Avargere. The incidence of A.flavus that produces aflatoxin highlights the necessity of taking action to eliminate their presence in food. The non-aflatoxigenic strains are being used in a biological control strategy to outcompete the aflatoxigenic ones.

Application of Non-Aflatoxigenic Aspergillus flavus for the Biological Control of Aflatoxin Contamination in China.

Biological control through the application of competitive non-aflatoxigenic Aspergillus flavus (A. flavus) to the soil during peanut growth is a practical method for controlling aflatoxin contamination. However, appropriate materials need to be found to reduce the cost of biocontrol products. In this study, a two-year experiment was conducted under field conditions in China, using a native non-aflatoxigenic strain to explore its effect. After three months of storage under high humidity, aflatoxin levels remained low in peanuts from fields treated with the biocontrol agent. Three types of substrates were tested with the biocontrol agent: rice grains, peanut meal (peanut meal fertilizer) and peanut coating. Compared to untreated fields, these formulations resulted in reductions of 78.23%, 67.54% and 38.48%, respectively. Furthermore, the ratios of non-aflatoxigenic A. flavus recovered in the soils at harvest in the treated fields were between 41.11% and 96.67% higher than that in untreated fields (25.00%), indicating that the rice inoculum was the most effective, followed by the peanut meal fertilizer and peanut coating. In 2019, the mean aflatoxin content of freshly harvested peanuts in untreated fields was 19.35 µg/kg higher than that in the fields treated with 7.5 kg/ha rice inoculum, which was 1.37 µg/kg. Moreover, no aflatoxin was detected in the two other plots treated with 10 and 15 kg/ha rice inoculum. This study showed that the native Chinese non-aflatoxigenic strain of A. flavus (18PAsp-zy1) had the potential to reduce aflatoxin contamination in peanuts. In addition, peanut meal can be used as an alternative substrate to replace traditional grains, reducing the cost of biocontrol products.

Non-aflatoxigenic kojic acid-producing Aspergillus flavus NJC04 reduces the symptoms of Sclerotinia sclerotiorum in soybean

Although non-aflatoxigenic Aspergillus flavus strains have been thoroughly used to reduce aflatoxin contaminations in maize and nuts, the biocontrol potential of these strains for the management of fungal pathogens remains almost unexplored. This study aimed to evaluate the biocontrol mechanisms and efficacy of A. flavus NJC04, which was previously isolated from kiwifruit, for the control of soybean pathogen Sclerotinia sclerotiorum. Non-aflatoxigenic NJC04 was shown to contain important deletions in the aflatoxin and cyclopiazonic acid biosyntheses. Interestingly, this strain inhibited mycelial growth and sclerotia formation of soybean pathogen Sclerotinia sclerotiorum. NJC04 showed various antifungal mechanisms against S. sclerotiorum, including competition for space and nutrients, and the production of antifungal kojic acid, which was detected at 87 ± 4 mg/L in the culture medium. NJC04 colonized soybean plants during long periods and did not cause necrotic lesions. Preventive application of 1 × 107 and 1 × 108 NJC04 spores/mL reduced Sclerotinia rot symptoms by 83.2 % and 100 %, respectively. Collectively, the biocontrol efficacy of non-aflatoxigenic NJC04 for the control of S. sclerotiorum was examined for the first time revealing new insights into the mechanisms used by A. flavus strains to compete with plant fungal pathogens.

Assessment of the Potential of a Native Non-Aflatoxigenic Aspergillus flavus Isolate to Reduce Aflatoxin Contamination in Dairy Feed.

Aspergillus species can produce aflatoxins (AFs), which can severely affect human and animal health. The objective was to evaluate the efficacy of reducing AF contamination of a non-aflatoxigenic isolate of A. flavus experimentally coinoculated with different aflatoxigenic strains in whole plant (WP), corn silage (CS), immature grains (IG) and in culture media (CM). An L-morphotype of A. flavus (CS1) was obtained from CS in a dairy farm located in the Mexican Highland Plateau; The CS1 failed to amplify the AFs biosynthetic pathway regulatory gene (aflR). Monosporic CS1 isolates were coinoculated in WP, CS, IG and CM, together with A. flavus strains with known aflatoxigenic capacity (originating from Cuautitlán and Tamaulipas, Mexico), and native isolates from concentrate feed (CF1, CF2 and CF3) and CS (CS2, CS3). AF production was evaluated by HPLC and fungal growth rate was measured on culture media. The positive control strains and those isolated from CF produced a large average amount of AFs (15,622 ± 3952 and 12,189 ± 3311 µg/kg), whereas A. flavus strains obtained from CS produced a lower AF concentration (126 ± 25.9 µg/kg). CS1 was efficient (p < 0.01) in decreasing AF concentrations when coinoculated together with CF, CS and aflatoxigenic positive control strains (71.6–88.7, 51.0–51.1 and 63.1–71.5%) on WP, CS, IG and CM substrates (73.9–78.2, 65.1–73.7, 63.8–68.4 and 57.4–67.6%). The results suggest that the non-aflatoxigenic isolate can be an effective tool to reduce AF contamination in feed and to minimize the presence of its metabolites in raw milk and dairy products intended for human nutrition.

Development of biochar-impregnated alginate beads for the delivery of biocontrol agents for peanut aflatoxin

The competitive inhibition of aflatoxigenic fungi by non-aflatoxigenic Aspergillus flavus has proved to be an effective method to prevent and control peanut aflatoxin contamination, and most of the currently used inoculum carriers are grains. In this study, the reliability and efficiency of replacing grain kernels with novel chitosan-coated alginate-poly(N-isopropylacrylamide) (PNIPAAm) beads impregnated with biochar (CSACB) were evaluated. Characterisation of the beads was performed by SEM, thermogravimetry analysis (TGA), and swelling properties analyses. The optimised CSACB beads had good physical stability, shelf life, and entrapment efficiency. In addition, the water-holding capacity and porous structure were excellent, as the biochar provided a beneficial microenvironment for the attachment and microbial growth of the biocontrol fungus. The effect of reducing aflatoxin in peanuts was verified experimentally. Collectively, the novel CSACB beads are suitable carriers of non-aflatoxigenic A. flavus for the biocontrol of peanut aflatoxin.

Cumulative Effects of Non-Aflatoxigenic Aspergillus flavus Volatile Organic Compounds to Abate Toxin Production by Mycotoxigenic Aspergilli.

Previously, authors reported that individual volatile organic compounds (VOCs) emitted by non-aflatoxigenic Aspergillus flavus could act as a mechanism of biocontrol to significantly reduce aflatoxins and cyclopiazonic acid (CPA) produced by toxigenic strains. In this study, various combinations and volumes of three mycotoxin-reductive VOCs (2,3-dihydrofuran, 3-octanone and decane) were assessed for their cumulative impacts on four Aspergillus strains (LA1–LA4), which were then analyzed for changes in growth, as well as the production of mycotoxins, including aflatoxins, CPA and multiple indole diterpenes. Fungal growth remained minimally inhibited when exposed to various combinations of VOCs. No single combination was able to consistently, or completely, inhibit aflatoxin or CPA across all toxigenic strains tested. However, the combination of 2,3-dihydrofuran and 3-octanone offered the greatest overall reductions in aflatoxin and CPA production. Despite no elimination of their production, findings showed that combining VOCs produced solely by non-aflatoxigenic A. flavus still inhibited several agriculturally important mycotoxins, including B and G aflatoxins and CPA. Therefore, other VOC combinations are worth testing as post-harvest biocontrol treatments to ensure the prolonged effectiveness of pre-harvest biocontrol efforts.

Comparison of the performance of metal oxide and conducting polymer electronic noses for detection of aflatoxin using artificially contaminated maize

The electronic nose offers potential as a rapid and cost effective field portable diagnostic device that would allow for quick screening of produce for aflatoxin contamination at the market entry level. This study aimed to compare the performance of three electronic nose sensor technologies: metal oxide semiconductor sensors (Fox 3000), conducting polymer sensors (Cyranose 320) and doped metal oxide semiconductor sensors with thermocycling (DiagNose), for the detection of volatiles associated with maize contaminated with aflatoxins. Australian maize (variety DK703w) samples were artificially inoculated with aflatoxigenic and non-aflatoxigenic Aspergillus flavus isolates and 2 % v/v Tween 20 as a control. Mutual information was used to select features from the electronic nose sensor signals for classification of the samples. The effectiveness, of selected features to discriminate between the different classes of samples was evaluated by support vector machines and k-nearest neighbour with leave-one-out cross-validation. Cross-validated classification accuracy for the different sample classes ranged from 81 % to 94 % for DiagNose, 76 to 79 % for Fox 3000 and 68 to 75 % for Cyranose. The results suggest that an electronic nose equipped with doped metal oxide semiconductor sensors and thermocycling is more effective for detection of aflatoxin contamination of maize.

Analysis of the competitiveness between a non-aflatoxigenic and an aflatoxigenic Aspergillus flavus strain on maize kernels by droplet digital PCR

Non-aflatoxigenic Aspergillus flavus strains are used as a biocontrol system on maize fields to decrease the aflatoxin biosynthesis of aflatoxigenic A. flavus strains. A. flavus strain AF36 was the first commercially available biocontrol strain and is authorized for use on maize fields by the US Environmental Protection Agency, e.g., in Texas and Arizona. A droplet digital PCR (ddPCR) assay was developed to analyze the mechanisms of competition and interaction of aflatoxigenic and non-aflatoxigenic A. flavus strains. This assay enables the parallel identification and quantification of the biocontrol strain A. flavus AF36 and the aflatoxigenic A. flavus strain MRI19. To test the assay, spores of both strains were mixed in varying ratios and were incubated on maize-based agar or maize kernels for up to 20 days. Genomic equivalent ratios (genome copy numbers) of both strains were determined by ddPCR at certain times after incubation and were compared to the spore ratios used for inoculation. The aflatoxin biosynthesis was also measured. In general, A. flavus MRI19 had higher competitiveness in the tested habitats compared to the non-aflatoxigenic strain, as indicated by higher final genomic equivalent ratios of this strain compared to the spore ratios used for inoculation. Nevertheless, A. flavus AF36 effectively controlled aflatoxin biosynthesis of A. flavus MRI19, as a clear aflatoxin inhibition was already seen by the inoculation of 10% spores of the biocontrol strain mixed with 90% spores of the aflatoxigenic strain compared to samples inoculated with only spores of the aflatoxigenic A. flavus MRI19.

Genetic Responses and Aflatoxin Inhibition during Co-Culture of Aflatoxigenic and Non-Aflatoxigenic Aspergillus flavus.

Aflatoxin is a carcinogenic mycotoxin produced by Aspergillus flavus. Non-aflatoxigenic (Non-tox) A. flavus isolates are deployed in corn fields as biocontrol because they substantially reduce aflatoxin contamination via direct replacement and additionally via direct contact or touch with toxigenic (Tox) isolates and secretion of inhibitory/degradative chemicals. To understand touch inhibition, HPLC analysis and RNA sequencing examined aflatoxin production and gene expression of Non-tox isolate 17 and Tox isolate 53 mono-cultures and during their interaction in co-culture. Aflatoxin production was reduced by 99.7% in 72 h co-cultures. Fewer than expected unique reads were assigned to Tox 53 during co-culture, indicating its growth and/or gene expression was inhibited in response to Non-tox 17. Predicted secreted proteins and genes involved in oxidation/reduction were enriched in Non-tox 17 and co-cultures compared to Tox 53. Five secondary metabolite (SM) gene clusters and kojic acid synthesis genes were upregulated in Non-tox 17 compared to Tox 53 and a few were further upregulated in co-cultures in response to touch. These results suggest Non-tox strains can inhibit growth and aflatoxin gene cluster expression in Tox strains through touch. Additionally, upregulation of other SM genes and redox genes during the biocontrol interaction demonstrates a potential role of inhibitory SMs and antioxidants as additional biocontrol mechanisms and deserves further exploration to improve biocontrol formulations.

Analysis of microbial community and the characterization of Aspergillus flavus in Liuyang Douchi during fermentation

Liuyang Douchi is a kind of traditional fermented Aspergillus-type Douchi in China for excellent favor. However, studies on the microbial diversity and the characterization of predominate fungi of Liuyang Douchi are few. In present study, the Illumina HiSeq sequencing was performed to reveal the fluctuation characteristics of microbial diversity during fermentation. Results showed that Staphylococcus (33.86%), Staphylococcaceae_unclassified (27.39%) and Pediococcus (8.80%) were the dominated bacteria, while Petromyces (74.57%), Rhizopus (10.93%) and Penicillium (2.68%) were the most predominant fungi during entire fermentation period. Intriguingly, Petromyces was negatively correlated with Alternaria, Saccharomyces and Saccharomycetales_unclassified. Further, four non-aflatoxigenic Aspergillus flavus strains were first identified and isolated from Liuyang Douchi according to phylogenetic and macroscopic characteristics. These four Aspergillus flavus displayed high cellulase and protease activities, but weak lipase activity. This study could contribute to the quality control of Liuyang Douchi by providing an overview of the microbial diversity.

The potential role of fungal volatile organic compounds in Aspergillus flavus biocontrol efficacy

Pre-harvest application of inherently non-aflatoxigenic Aspergillus flavus strains is an effective biocontrol strategy to minimize aflatoxin contamination of agricultural commodities, but researchers still do not fully understand how A. flavus biocontrol strains establish control over aflatoxigenic fungi. In this in vitro study, we tested the potential for A. flavus volatile organic compounds (VOCs), identified from a previous study, to serve as regulators of mycotoxin production. We exposed four Aspergillus strains (one non-aflatoxigenic and three aflatoxigenic) to five VOCs unique to aflatoxigenic A. flavus, and five VOCs unique to non-aflatoxigenic A. flavus, to study their impacts on growth as well as production of two mycotoxins: aflatoxin and cyclopiazonic acid (CPA). We found that growth of the fungi was not severely impacted by VOCs. However, toxin production was greatly affected and highly variable between strains and VOCs. Two non-aflatoxigenic VOCs (3-octanone and trans-2-methyl-2-butenal) significantly reduced aflatoxins in all aflatoxigenic strains. Two other non-aflatoxigenic VOCs (2,3-dihydrofuran and decane) significantly reduced aflatoxin levels in all aflatoxigenic strains and each VOC completely inhibited CPA production in one aflatoxigenic strain. Our findings offer evidence that the mechanism of control implemented by biocontrol strains may involve chemosensing through the production of one or more VOCs. These findings can be used to identify natural selectable markers for improved biocontrol strains or to supplement current biocontrol efforts through post-harvest exposure to VOC-related chemicals that mimic the presence of biocontrol strains.

Effect of non-aflatoxigenic strains of Aspergillus flavus on aflatoxin contamination of pre-harvest peanuts in fields in China

Aflatoxin contamination of peanuts is one of the most concerns in peanut production in China. Applying non-aflatoxigenic Aspergillus flavus strains, based on competitive exclusion, has been proved to be a promising strategy to reduce aflatoxin contamination in pre-harvest peanuts. Two non-aflatoxigenic A. flavus strains collected in China, which have been proved effectively reducing aflatoxin in the laboratory, were mixed with high aflatoxin producer to the soil in peanut growing season. The two non-aflatoxigenic strains significantly (P ​< ​0.05) reduced aflatoxin contamination in peanut kernels under both normal and drought stresses in two fields. Compared to control, the total aflatoxin (sum of aflatoxin B1 and B2) was reduced 26.7–99.12% in field 1, and 84.96–99.33% in field 2. The aflatoxin was reduced 84.96–99.33% under drought stress in two fields. The present study indicated the non-aflatoxigenic A. flavus strains could be potential biocontrol agents for reducing aflatoxin contamination under field condition.

Chromolaena laevigata (Asteraceae) as a source of endophytic non-aflatoxigenic Aspergillus flavus: chemical profile in different culture conditions and biological applications.

Endophytes are microorganisms that form symbiotic relationships with their host. These microorganisms can produce a variety of secondary metabolites, some of which have inhibitory effects on pests and pathogens or even act to promote plant growth. Due to these characteristics, these microorganisms are used as sources of biologically active substances for a wide range of biotechnological applications. Based on that, the aim of this study was to evaluate the production of metabolites of the endophytic Aspergillus flavus CL7 isolated from Chromolaena laevigata, in four different cultivation conditions, and to determine the antimicrobial, cytotoxic, antiviral, and antioxidant potential of these extracts. The multiphasic approach used to identify this strain was based on morphology and ITS gene sequence analysis. The chemical investigation of A. flavus using potato dextrose and minimal medium, using both stationary and agitated methods, resulted in the isolation of kojic acid, α-cyclopiazonic acid, and 20,25-dihydroxyaflavinine. Another 18 compounds in these extracts were identified by UHPLC-HRMS/MS, of which dideacetyl parasiticolide A has been described for the first time from A. flavus. Aflatoxins, important chemomarkers of A. flavus, were not detected in any of the extracts, thus indicating that the CL7 strain is non-aflatoxigenic. The biological potential of all extracts was evaluated, and the best results were observed for the extract obtained using minimal medium against Trichophyton rubrum and Mycobacterium tuberculosis.

Morphological Characterization and Determination of Aflatoxigenic and Non-Aflatoxigenic Aspergillus flavus Isolated from Sweet Corn Kernels and Soil in Malaysia

This study aimed to morphologically characterize and determine the aflatoxigenic and non-aflatoxigenic Aspergillus flavus isolates. Forty isolates of A. flavus were obtained from sweet corn kernels and soil samples collected from Kampong Raja, Rose Valley, Kea, and Klebang farms in Malaysia. They were cultured on potato dextrose agar (PDA), dichloran rose-bengal chloramphenicol (DRBC), Aspergillusflavus and Aspergillus parasiticus agar (AFPA), and coconut cream agar (CCA). Macromorphological characteristics were determined by observing the colony color and texture, while the micromorphological characteristics were determined by examining the spore color, size, structure, conidiophore structure, and vesicle shape. The production of aflatoxin was determined by direct visualization of the UV fluorescence of A. flavus colonies on CCA. Aflatoxin was qualitatively detected in 18 (45%) isolates of A. flavus using UV fluorescence screening while the remaining 22 (55%) isolates did not exhibit any aflatoxin production. The highest incidence of A. flavus (30%) and aflatoxin production (15%) was recorded in samples from Kampong Raja. On the other hand, isolates from Rose Valley (17%) and Kea (12%) were non-aflatoxigenic. Klebang recorded a 25% incidence of A. flavus in which 15% were aflatoxigenic while 10% were non-aflatoxigenic. The occurrence of aflatoxin-producing A. flavus emphasizes the need for the measure to eradicate their presence in food crops. A biological control treatment utilizing the non-aflatoxigenic strains to compete with the aflatoxigenic ones is underway. Validation of aflatoxin production through high performance liquid chromatography is also ongoing.

A non-toxigenic Aspergillus flavus strain prevents the spreading of Fusarium verticillioides and fumonisins in maize

We evaluated Fusarium verticillioides and fumonisin contamination in maize samples after application of a non-aflatoxigenic Aspergillus flavus strain in the field. The sampling was performed 150 days after planting. The results showed a reduction in F. verticillioides frequency, as well as in fumonisin levels when samples were obtained from field areas treated with non-aflatoxigenic A. flavus strain. These results suggested a competition for substrate or space between fungi reducing the frequency of F. verticillioides and, consequently, fumonisin production.

Gas Chromatography-Mass Spectrometry Profiling of Volatile Compounds Reveals Metabolic Changes in a Non-Aflatoxigenic Aspergillus flavus Induced by 5-Azacytidine.

Aspergillus flavus is one of the most opportunistic pathogens invading many important oilseed crops and foodstuffs with such toxic secondary metabolites as aflatoxin (AF) and Cyclopiazonic acid. We previously used the DNA methylation inhibitor 5-azacytidine to treat with an AF-producing A. flavus A133 strain, and isolated a mutant (NT) of A. flavus, which displayed impaired abilities of AF biosynthesis and fungal development. In this study, gas chromatography–mass spectrometry (GC-MS) analysis was used to reveal the metabolic changes between these two strains. A total of 1181 volatiles were identified in these two strains, among which 490 volatiles were found in these two strains in vitro and 332 volatiles were found in vivo. The NT mutant was found to produce decreasing volatile compounds, among which most of the fatty acid-derived volatiles were significantly downregulated in the NT mutant compared to the A133 strain, which are important precursors for AF biosynthesis. Two antioxidants and most of the amino acids derived volatiles were found significantly upregulated in the NT mutant. Overall, our results reveal the difference of metabolic profiles in two different A. flavus isolates, which may provide valuable information for controlling infections of this fungal pathogen.

The role of extrolites secreted by nonaflatoxigenic Aspergillus flavus in biocontrol efficacy.

Field control of aflatoxin contamination is thought to occur through competitive exclusion of native aflatoxigenic fungi by introduced nonaflatoxigenic Aspergillus flavus biocontrol strains. In this study, we explored another possible mechanism that could increase the efficacy of biocontrol strains-the production of secreted compounds termed extrolites. Using four Aspergillus strains (one nonaflatoxigenic and three aflatoxigenic) from the same geographic region (Louisiana), we devised experiments whereby each aflatoxigenic strain was grown on media that had first been colonized by the nonaflatoxigenic strain. We observed noticeable reduction in growth and reduced production of aflatoxin and cyclopiazonic acid for all three aflatoxigenic strains when grown in the presence of extrolite secretions from the nonaflatoxigenic strain. We provide evidence that biocontrol strain extrolites may improve the efficacy of pre and postharvest aflatoxin reduction. Our finding, that extrolites secreted by nonaflatoxigenic A. flavus strains potentially abate growth and toxin levels of aflatoxin-producing strains, should allow for us to elucidate the mechanism of how the reduction in toxigenic strains occurs, and potentially identify better biocontrol strains. Identification and isolation of the active extrolites may afford a supplemental method to mitigate aflatoxin production.