Evaluation of atoxigenic isolates of Aspergillus flavus as potential biocontrol agents for aflatoxin in maize

Aflatoxin contamination resulting from maize infection by Aspergillus flavus is both an economic and a public health concern. Therefore, strategies for controlling aflatoxin contamination in maize are being investigated. The abilities of eleven naturally occurring atoxigenic isolates in Nigeria to reduce aflatoxin contamination in maize were evaluated in grain competition experiments and in field studies during the 2005 and 2006 growing seasons. Treatments consisted of inoculation of either grains in vials or ears at mid-silking stage in field plots, with the toxigenic isolate (La3228) or atoxigenic isolate alone and co-inoculation of each atoxigenic isolate and La3328. Aflatoxin B(1) + B(2) concentrations were significantly (p < 0.05) lower in the co-inoculation treatments compared with the treatment in which the aflatoxin-producing isolate La3228 was inoculated alone. Relative levels of aflatoxin B(1) + B(2) reduction ranged from 70.1% to 99.9%. Among the atoxigenics, two isolates from Lafia, La3279 and La3303, were most effective at reducing aflatoxin B(1) + B(2) concentrations in both laboratory and field trials. These two isolates have potential value as agents for the biocontrol of aflatoxin contamination in maize. Because these isolates are endemic to West Africa, they are both more likely than introduced isolates to be well adapted to West African environments and to meet regulatory concerns over their use throughout that region.     

Aflatoxin and Cyclopiazonic Acid Production by Aspergillus flavus Isolated from Contaminated Maize

Seven truck-loads of maize were tested for mycotoxin contamination. Aflatoxin was identified in all 7 at concentrations from 3 ng/g-501 ng/g (aflatoxin B₁+ B₂). Cyclopiazonic acid was identified in 4 loads with concentrations from 25-250 ng/g. Deoxynivalenol was found in 4 of 5 loads tested, over a range of 46-676 ng/g. Ninteeen isolates of Aspergillus flavus from the samples were tested for ability to accumulate cyclopiazonic acid and aflatoxin in liquid culture. Fourteen produced cyclopiazonic acid (0.5-135 μg/mL), 12 produced aflatoxin (0.01-0.70 μg/mL, aflatoxin B₁+ B₂), and one aflatoxin-producing isolate did not produce cyclopiazonic acid.     

Aflatoxin occurrence in milk and supplied concentrates of goat farms of north‐eastern Italy

BACKGROUND: There is little information about the occurrence of aflatoxin M₁ in goat milk. A survey involving 17 dairy goat farms of north‐eastern Italy was completed during 2005 and 2006, in order to evaluate the prevalence of milk contamination and its relationship with type and level of concentrate supplied. RESULTS: 132 concentrate and 85 milk samples were collected during five farm visits and analysed for aflatoxins. Aflatoxin B₁ (AFB₁) was > 0.1 µg kg^?1 in two‐thirds of the feeds and > 5 µg kg^?1 in nine. Contamination was higher in maize than in other pure feeds (median: 0.8 versus 0.1 µg kg^?1); complementary feeds showed intermediate values. Aflatoxin M₁ (AFM₁) was > 3 ng kg^?1 in one‐third of milks and > 25 ng kg^?1 in three. All the milk samples were below EU statutory limits. The farm ranks for milk AFM₁ level and the peak of concentrate AFB₁ contamination were significantly correlated (0.642). CONCLUSIONS: Risk to human health was generally found to be absent, with only a few cases involving feed contamination to be monitored. The main aflatoxin risk for goat milk could arise from maize and maize‐based concentrates in the more intensive breeding conditions. Copyright © 2008 Society of Chemical Industry     

Fungi associated with post-harvest rot of sweet orange (Citrus sinensis) and aflatoxin B1 production by isolates of Aspergillus flavus on plain and supplemented orange juice

Samples of rotting sweet orange (Citrus sinensis) were obtained from the depots, sales counters and waste baskets. Fungi associated with rotting fruits were isolated and identified. Out of 12 species of fungi isolated, 8 are known to be producers of toxins. The 7 isolates of Aspergillus flavus obtained were screened for aflatoxin production in a nutrient solution, and 4 were found to be aflatoxigenic, producing primarily aflatoxin B₁. Aflatoxin B₁ production of the toxigenic isolates were further studied on plain juice and juice separately supplemented with 2.0% yeast extract and 2.0% sucrose. The highest yield of aflatoxin B₁ was produced on juice supplemented with yeast extract by the 4 toxigenic A. flavus isolates, followed by sucrose supplementation while the lowest amount of aflatoxin B₁ was detected on plain juice. Optimum temperature for aflatoxin B₁ production by A. flavus isolate (IBA-O1) was 25 °C to 30 °C, for an incubation period of 7–11 days on plain and supplemented juice media.     

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

Aflatoxins are highly toxic carcinogens produced by several species in Aspergillus section Flavi. Strains of A. flavus that do not produce aflatoxins, called atoxigenic strains, have been used commercially in North America as tools for limiting aflatoxin contamination. A similar aflatoxin management strategy is being pursued in Nigeria. In the current study, loci across the 68 kb aflatoxin biosynthesis gene cluster were compared among 18 atoxigenic and two aflatoxin-producing vegetative compatibility groups (VCGs) from Nigeria and an atoxigenic VCG used commercially in North America. Five of the atoxigenic VCGs had large deletions (37–65 kb) extending from the teleomeric side of the aflatoxin biosynthesis cluster. In one VCG (AV0222) the deletion extended through the cluster to the adjacent sugar cluster. The remaining twelve atoxigenic VCGs, including the VCG used for aflatoxin management in North America, contained all the aflatoxin pathway genes, but with defects. Two observations support the long-term persistence of atoxigenicity within A. flavus: first, a comparison of pathway genes revealed more changes in atoxigenic than in aflatoxin-producing isolates relative to the aflatoxin-producing strain NRRL 3357; and second, several non-synonymous changes are unique to atoxigenics. Atoxigenic VCG diversity was assessed with phylogenetic analyses. Although some atoxigenics share relatively recent ancestry, several are more closely related to aflatoxin producers than to other atoxigenics. The current study demonstrates VCGs of A. flavus in West Africa with diverse mechanisms of atoxigenicity and potential value in aflatoxin management programmes.     

Influence of the cropping pattern on aflatoxin contamination in preharvest Kharif (monsoon) maize crop (Zea mays)

Aflatoxin contamination in three varieties of maize (Zea mays L), viz Diara composite, M₉ and Suwan composite, under various cultivation rates and planting densities was examined during the 1987 and 1989 Kharif (monsoon) crops. Cultivation rates comprising single line weeding (SLW) with one spading, SLW with two spadings and SLW with three spadings did not have significant effects on aflatoxin production in the preharvest standing crop. Of the three planting populations, the toxin level was highest under 56000 plants ha^?1 followed by 83000 plants ha^?1, and 67000 plants ha^?1 in Aspergillus flavus inoculated plots (I₁) and uninoculated plots (I₀), respectively. The variety M₉ was most susceptible to A flavus infection and supported higher aflatoxin production under I₁ condition. Aflatoxin concentration was lowest in Diara composite. Correlation analysis showed a positive and highly significant relation between A flavus incidence and aflatoxin contamination (r = +0.73, P < 0.01).     

Aflatoxin B1-degrading activity from Bacillus subtilis BCC 42005 isolated from fermented cereal products

ABSTRACT

Aflatoxin B₁ is a naturally occurring mycotoxin that is produced as secondary metabolite by Aspergillus spp., especially A. flavus and A. parasiticus. This is the most severe toxin due to its carcinogenic, mutagenic, and teratogenic properties. Hence, methods for toxin degradation have been received increasing interest from both scientific communities and industries. In this study, 32 isolates of Bacillus spp. from various fermented cereal products were screened for their aflatoxin B₁ degradation ability. The results indicated the extracellular fraction of Bacillus subtilis BCC 42005 isolated from Iru (African locust bean) potentially possessed aflatoxin B₁-degrading ability. The maximum activity of the active fraction was at 50°C and pH 8.0. The activity was stable in a wide range of pH (5.0–8.0) and temperature (25–60°C). The aflatoxin B₁-degrading mechanisms of this strain may be possibly involved by enzyme(s). This extracellular fraction was not toxic at IC₅₀ 4 mg/ml and it can be combined with water as a soaking agent for maize, which results in 54% of aflatoxin B₁ reduction after contact time 120 min. Hence, the extracellular fraction of Bacillus subtilis BCC 42005 can be further applied as an effective soaking agent in a pretreatment process with a practical and easy-to-implement condition and also probably used to reduce the aflatoxin B₁ contamination in other foods and feeds commodities.     

Aflatoxin accumulation in whole crop maize silage as a result of aerobic exposure

BACKGROUND: Most of the maize silage stored in horizontal silos is exposed to air and can be spoiled by fungi. Potentially toxigenic fungi have been found in maize silage, and about 300 mycotoxins have been detected. Among these mycotoxins, the most harmful for feed and food safety are aflatoxins. The aim of the study was to set up a specific method to detect aflatoxins in maize silage, and to investigate whether aflatoxin contamination in maize silage depends on the level of field contamination of the crop, and whether the occurrence of aerobic spoilage during ensiling has any effect on the final contamination of the silage. RESULTS: A method for the determination of aflatoxin B₁, B₂, G₁ and G₂ in maize silage using high‐performance liquid chromagraphy with fluorescence detection has been developed and validated. Recoveries of aflatoxin B₁, B₂, G₁, and G₂ spiked over the 0.25 to 5 µg kg^?1 range averaged 74–94%. The results of laboratory scale and farm scale ensiling experiments indicated that aflatoxins could increase when silage is exposed to air during conservation or during the feed‐out phase. CONCLUSIONS: The method here proposed to detect aflatoxins in silages has proved to be sensitive and is able to detect levels of 0.1 and 0.5 ng mL^?1 for AFB₁ and AFG₁, and between 0.025 and 0.125 ng mL^?1 for AFB₂ and AFG₂. This study also provides evidence of aflatoxin accumulation in whole crop maize silage as a result of aerobic exposure. Copyright © 2011 Society of Chemical Industry     

不产毒黄曲霉菌对产毒黄曲霉菌产毒抑制效果分析

本实验6株菌分离自广东、山东、辽宁和湖北四省的花生土壤中,通过形态学和分子生物学鉴定均为黄曲霉菌,HPLC测定其产毒能力,其中GZ-6为产毒菌,GZ-15、WF-5、WF-20、JZ-2和YC-8为不产毒菌。分别以花生和玉米为培养基,将不产毒黄曲霉菌和产毒菌(孢子浓度:104:105或105:105)进行混合培养,测定不产毒菌对产毒黄曲霉产毒的抑制效果。结果显示:不产毒菌对产毒菌产毒的抑制率随着其孢子浓度的增加而明显加强,当孢子浓度比为105:105(不产毒菌:产毒菌)时,5株不产毒菌在玉米培养基上对产毒菌产毒的抑制率为34.55%~75.94%,在花生培养基上对产毒菌产毒的抑制率为38.03%~83.03%,其中WF-5、WF-20和GZ-15这三株不产毒菌对产毒黄曲霉产毒的抑制效果均达到75.00%以上,可以作为田间防治黄曲霉毒素污染的候选菌株。     

Aflatoxins in sunflower and safflower seeds from Iran

Aflatoxin content of 173 sunflower and safflower seeds was determined by HPLC with immunoaffinity column (IAC) clean-up and fluorometric detection. Aflatoxin B₁ contamination was found in 111 samples: in 8 of the sunflower seed samples (16%) at a mean level of 40.68?ng?g^?1 and in 103 safflower seed samples (83.7%) at a mean level of 2.81?±?0.44?ng?g^?1. In 5 sunflower seed samples and 1 safflower seed sample, aflatoxin B₁ levels were higher than the maximum levels of AFB₁ under Iran regulations (5?ng?g^?1). Aflatoxin B₁ levels in 5 sunflower and 2 safflower seed samples were higher than the European Union maximum limit (2?ng?g^?1).     

Aspergillus and aflatoxin in groundnut (Arachis hypogaea L.) and groundnut cake in Eastern Ethiopia

This study was conducted to assess major Aspergillus species and aflatoxins associated with groundnut seeds and cake in Eastern Ethiopia and evaluate growers’ management practices. A total of 160 groundnut seed samples from farmers’ stores and 50 groundnut cake samples from cafe and restaurants were collected. Fungal isolation was done from groundnut seed samples. Aspergillus flavus was the dominant species followed by Aspergillus parasiticus. Aflatoxin analyses of groundnut seed samples were performed using ultra performance liquid chromatography; 22.5% and 41.3% of samples were positive, with total aflatoxin concentrations of 786 and 3135 ng g^?1 from 2013/2014 and 2014/2015 samples, respectively. The level of specific aflatoxin concentration varied between 0.1 and 2526 ng g^?1 for B₂ and B₁, respectively. Among contaminated samples of groundnut cake, 68% exhibited aflatoxin concentration below 20 ng g^?1, while as high as 158 ng g^?1 aflatoxin B₁ was recorded. The study confirms high contamination of groundnut products in East Ethiopia.     

Natural occurrence of aflatoxin B1 in sorghum grown in different geographical regions of India

BACKGROUND: Sorghum (Sorghum bicolor (L.) Moench) is an important coarse cereal crop grown for grain and fodder in the semi‐arid Tropics, mainly in Asian and African countries. In India sorghum is consumed as human food and poultry feed. Sorghum grain grown in the rainy season (kharif) is becoming severely affected by grain moulds, the major fungi involved being Aspergillus, Fusarium and Curvularia. If the extent of mould is severe, the grain is unsafe for consumption owing to contamination by mycotoxins. RESULTS: This paper presents a multi‐centre study conducted in sorghum to evaluate natural contamination of aflatoxin B₁ in India. A total of 1606 grain sorghum samples were collected during the rainy (kharif) season across 4 years from seven states of India, representing different geographical regions of the country. Aflatoxin B₁ contamination during 2007–08 was the highest (13.1%), followed by samples from the year 2004–05 (2.85%). The samples collected in years 2005–06 and 2006–07 showed contamination below 1%. The number of samples (35) showing aflatoxin B₁ contamination above the safety limit was also highest during 2007–08 as compared to samples from the other years. CONCLUSION: This study, conducted for 4 years, showed that natural contamination of aflatoxin B₁ in sorghum grown in India is within safety limits (20 µg kg^?1) recommended by the Codex Alimentarius Committee and 73% of samples were positive for toxin. However, 0.75% (12) of total samples contained aflatoxin above the safety limit. The overall occurrence of toxin from Madhya Pradesh and Rajasthan was below 5 µg kg^?1. Copyright © 2012 Society of Chemical Industry     

Modellversuche zur Aflatoxinbildung in Schmelzk?se

Zusammenfassung Schmelzkäse stellt fürAspergillus favus ein sehr gutes Substrat dar. Nach 16 tägiger Kulturdauer konnten folgende Aflatoxinmengen nachgewiesen werden: 35 ppm Aflatoxin B₁, 66 ppm Aflatoxin G₁, 8,6 ppm Aflatoxin B₂, 5,3 ppm Aflatoxin G₂ und 2,1 ppm Aflatoxin M₁. Eine Erhöhung der Schmelzsalzkonzentration von 3% auf 8% bzw. ein Zusatz von 6% Natriumchlorid reduzierten das Toxinbildungsvermögen vonAspergillus favus deutlich.

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Simulation of natural mould growth in processed cheese

Summary Processed cheese is a very good substrate forAspergillus flavus. After 16 days incubation, a processed cheese inoculated withAspergillus flavus was found to contain 35 ppm aflatoxin B₁, 66 ppm aflatoxin G₁, 8.6 ppm aflatoxin B₂, 5.3 ppm aflatoxin G₂ and 2.1 ppm aflatoxin M₁. An increase in the content of emulsifying salt from 3% to 8% caused a distinct decrease in the contents of aflatoxin B₁ and G₁ in the cheese, as did the addition of 6% sodium chloride.

     

乳及乳制品中黄曲霉毒素M1污染及检测技术研究进展

乳及乳制品中的黄曲霉毒素M_1是黄曲霉毒素B1的羟基化衍生物,对肝脏有致畸和致癌作用。随着人们生活水平的提高,乳及乳制品中黄曲霉毒素M_1污染也引起越来越多的关注。本文从不同品种、季节及地域分析乳及乳制品中黄曲霉毒素M_1污染水平,并综述了液相色谱法和免疫法的检测技术研究进展。     

Fungal contamination and aflatoxin content of maize,moringa and peanut foods from rural subsistence farms in South Haiti

Mycotoxins are toxic, low molecular weight compounds produced by fungi. Among them, aflatoxins are the most carcinogenic and they mainly impact on rural communities of developing countries. The present study supplies data on mycobiota and aflatoxin contamination in the most common food products consumed in Haiti. The study concerns analyses performed on 49 samples of meals and seeds collected in South Haiti and tested for fungal occurrence and aflatoxin content by HPLC-DAD technique. The results revealed that three main fungal genera affected Haitian food products: Aspergillus spp. (Section Flavi and Nigri), followed by Penicillium spp. and Fusarium spp. Aflatoxin was present in more than half of the samples of maize (Zea mays L.) kernels (55%), maize meal (57%) and moringa (Moringa oleifera Lam.) seeds (64%), and in 25% of peanut (Arachis hypogaea L.) samples. The tested food products were mostly contaminated by aflatoxin B₁ (AFB₁) followed by aflatoxin B₂ (AFB₂), while no aflatoxins type G were detected. The total concentration of aflatoxins in the positive samples was 228 μg/kg on average, i.e., fifty-seven and eleven times higher than the maximum levels allowed in Europe and USA, respectively. Both the presence of aflatoxigenic fungi and aflatoxin contamination in maize kernels seemed to be related to agricultural practices, such as weed control, irrigation and growing cycle length. These findings suggest that the Haitian population is strongly exposed to aflatoxin risk. This risk could be reduced by exploiting simple and accessible farming strategies for minimizing mycotoxin contamination, at least for maize.     

Abbau von Aflatoxin B1 durch verschiedene Mikroorganismen

Zusammenfassung Bei der Untersuchung des Abbaus von Aflatoxin B₁ durch verschiedene Vertreter der Bakterien, Hefen und Schimmelpilze in wachsenden und ruhenden Kulturen zeigten wachsende Kulturen vonCorynebacterium rubrum die stärkste Fähigkeit zum Abbau. Wachsende Kulturen von anascosporogenen Hefen bauten Aflatoxin B₁ relativ gut ab, während ein Abbau durch ascosporogene Hefen nicht festzustellen war. Schimmelpilze bauten Aflatoxin B₁ zu einem hohen Prozentsatz ab. — Nach dem Verlauf des Abbaus ließen sich drei Typen unterscheiden. — In Kulturen der Schimmelpilze wurden neben Aflatoxin B₁ zwei weitere fluorescierende Verbindungen nachgewiesen.

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Degradation of aflatoxin B₁ by various microorganisms

Summary The degradation of aflatoxin B₁ by various representatives of bacteria, yeasts and moulds in growing and resting cultures was investigated. We found that growing cultures ofCorynebacterium rubrum degraded the added aflatoxin nearly quantitatively. —Growing cultures of anascosporogenous yeasts degraded most of aflatoxin B₁ while no degradation of this substance by ascosporogenous yeasts could be stated. Moulds degraded. aflatoxin B₁ to a high extent. — With regard to the course of degradation three types can be distinguished. — In the cultures of moulds two blue fluorescing compounds were found beside aflatoxin B₁.

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Die Arbeit wurde von der Deutschen Forschungsgemeinschaft unterstützt     

Aflatoxins,ochratoxin A and zearalenone in Brazilian corn cultivars

Past surveys indicated that the occurrence of aflatoxins, zearalenone and ochratoxin A was not a problem in corn and corn products in the state of São Paulo, Brazil. However, according to recent studies, a change in pattern has been detected. To obtain a better overview, these toxins were searched for in 110 samples of freshly harvested corn, corresponding to 48 commercial cultivars planted at three different locations in the state. Aflatoxin contamination was found in 60 (54.5%) of the samples, in levels ranging from 6 to 1600 µg kg^?1 aflatoxin B₁. Insect control was exercised, so this was not the main route of corn infection. Endosperm type, germplasm type, number of days to flowering, and length of time the mature corn remained in the field had no effect on aflatoxin contamination. Ochratoxin A was found in two samples (206 and 128 µg kg^?1) and zearalenone in one sample (4640 µg kg^?1). Possible causes of the increase in aflatoxin levels may lie in the changing nature of the commercial cultivars employed, associated with the forsaking of the original landraces, and in a change in the toxigenicity pattern of the corn mycoflora Aspergillus flavus/Aspergillus parasiticus prevailing strains. © 2001 Society of Chemical Industry     

Mycotoxin contamination of home-grown maize in rural northern South Africa (Limpopo and Mpumalanga Provinces)

The aim of this study was to assess mycotoxin contamination of crops grown by rural subsistence farmers over two seasons (2011 and 2012) in two districts, Vhembe District Municipality (VDM, Limpopo Province) and Gert Sibande District Municiality (GSDM, Mpumalanga Province), in northern South Africa and to evaluate its impact on farmers’ productivity and human and animal health. A total of 114 maize samples were collected from 39 households over the two seasons and were analysed using a validated liquid chromatography-tandem mass spectrometry mycotoxins method. Aflatoxin B₁ (AFB₁) occurrence ranged from 1 to 133 µg kg^?1 in VDM while AFB₁ levels in GSDM were less than 1.0 µg kg^?1 in all maize samples. Fumonisin B₁ levels ranged from 12 to 8514 µg kg^?1 (VDM) and 11–18924 µg kg^?1 (GSDM) in 92% and 47% positive samples, respectively, over both seasons. Natural occurrence and contamination with both fumonisins and aflatoxins in stored home-grown maize from VDM was significantly (p < 0.0001) higher than from GSDM over both seasons.     

Aflatoxin at several initial concentrations is degraded by different amounts of mycelium of aspergillus parasiticus

Summary Increasing amounts of a blendure of 9-day-old mycelia ofAspergillus parasiticus NRRL 2999 added to aflatoxin-salts reaction mixtures resulted in increased rates at which aflatoxin B₁ and G₁ were degraded. Similarly, increasing the amount(s) of aflatoxin B₁ and/or G₁ in the aflatoxin-salts reaction mixture resulted in increased rates of degradation of aflatoxins B₁ and G₁ by mycelia. This mycelial blendure degraded aflatoxin G₁ approximately 1.6 times more rapidly than aflatoxin B t when comparable amounts of the aflatoxins were initially present. When the same mycelial blendure was used to compare combined effects of size of inoculum and initial aflatoxin concentration on aflatoxin degradation, it appeared that increasing the amount of either inoculum or aflatoxin resulted in a comparable increase in degradation of aflatoxin B₁ and G₁. Hence, doubling the amount of inoculum or of aflatoxin xesulted in approximately doubled rates at which aflatoxins B1 and G₁ were degraded.

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Abbau von Aflatoxin bei verschiedenen Anfangskonzentrationen durch unterschiedliche Mycel-Mengen von Aspergillus parasiticus

Zusammenfassung Wenn zunehmende Mengen von 9 Tage altem Mycel vonAspergillus parasiticus NRRL 2999 zu einem Aflatoxin-Salz-Gemisch gegeben wurden, dann stieg die Geschwindigkeit des Aflatoxinabbaues an. In gleicher Weise verursachten zunehmende Mengen von Alfatoxin B1 und/oder G₁ in dieser flüssigen Mischung eine größere Geschwindigkeit des Aflatoxinabbaues durch das Mycel. Das Mycel baute Aflatoxin G₁ 1,6-mal schneller ab als Aflatoxin B₁, wenn gleiche Mengen beider Aflatoxine am Anfang anwesend waren. Wenn die gleiche Mycel-Mischung angewandt wurde, um den kombinierten Effekt von Größe der Impfmenge und Aflatoxin-Anfangskonzentration auf den Aflatoxin-Abbau zu vergleichen, stieg bei einer erhöhten Impfmenge bzw. bei einer erhöhten Aflatoxin-Konzentration der Grad des Abbaues von Aflatoxin B₁ oder G₁ an. Bei Verdoppelung der Ansätze war der Abbau des Aflatoxin B₁ und G₁ ungefähr ebenfalls verdoppelt.

     

Nonaflatoxigenic Aspergillus flavus TX9-8 competitively prevents aflatoxin accumulation by A. flavus isolates of large and small sclerotial morphotypes

Aflatoxins are a family of highly toxic and carcinogenic toxins produced by several Aspergillus species. Aflatoxin contamination of agricultural commodities both pre- and postharvest is a serious food safety issue and a significant economic concern. Using nonaflatoxigenic A. flavus isolates to competitively exclude toxigenic A. flavus isolates in agricultural fields has become an adopted approach to reduce aflatoxin contamination. From screening subgroups of nonaflatoxigenic A. flavus, we identified an A. flavus isolate, TX9-8, which competed well with three A. flavus isolates producing low, intermediate, and high levels of aflatoxins, respectively. TX9-8 has a defective polyketide synthase gene (pksA), which is necessary for aflatoxin biosynthesis. Co-inoculating TX9-8 at the same time with large sclerotial (L strain) A. flavus isolates at a ratio of 1:1 or 1:10 (TX9-8:toxigenic) prevented aflatoxin accumulation. The intervention of TX9-8 on small sclerotial (S strain) A. flavus isolates varied and depended on isolate and ratio of co-inoculation. At a ratio of 1:1 TX9-8 prevented aflatoxin accumulation by A. flavus CA28 and reduced aflatoxin accumulation 10-fold by A. flavus CA43. No decrease in aflatoxin accumulation was apparent when TX9-8 was inoculated 24 h after toxigenic L- or S strain A. flavus isolates started growing. The competitive effect likely is due to TX9-8 outgrowing toxigenic A. flavus isolates.