Increased sensitivity of Aspergillus flavus and Aspergillus parasiticus aflatoxin biosynthesis polyketide synthase mutants to UVB light

2010 ◽  
Vol 3 (3) ◽  
pp. 263-270 ◽  
Author(s):  
K. Ehrlich ◽  
Q. Wei ◽  
D. Bhatnagar
Keyword(s):  
Aspergillus Flavus ◽  
Polyketide Synthase ◽  
Aspergillus Parasiticus ◽  
Aflatoxin Contamination ◽  
Aflatoxin Biosynthesis ◽  
Increased Sensitivity ◽  
Isogenic Mutants

One strategy to reduce aflatoxin contamination of maize and cottonseed is to introduce spores of non-aflatoxigenic strains as competitors. Using isogenic mutants we show that, upon 5 or 20 min exposure to 302 nm (UVB) light, the viability of conidia of Aspergillus flavus and Aspergillus parasiticus mutants lacking the ability to accumulate any aflatoxin precursor metabolite is reduced five-fold compared to that of aflatoxin-producing strains or pigmented mutants that accumulate aflatoxin precursors. This result suggests that the long-term viability of introduced non-aflatoxigenic competitor strains may be lower than that of natural aflatoxin-producing isolates when exposed to sunlight.

scholarly journals Vibrio gazogenes inhibits aflatoxin production through downregulation of aflatoxin biosynthetic genes in Aspergillus flavus

2022 ◽  
Author(s):  
Shyam L. Kandel ◽  
Rubaiya Jesmin ◽  
Brian M. Mack ◽  
Rajtilak Majumdar ◽  
Matthew K. Gilbert ◽  
...  
Keyword(s):  
Secondary Metabolites ◽  
Secondary Metabolite ◽  
Aspergillus Flavus ◽  
Fungal Biomass ◽  
Expression Profiles ◽  
Health Hazard ◽  
Gene Clusters ◽  
Aflatoxin Contamination ◽  
Aflatoxin Biosynthesis ◽  
Control Samples

Aspergillus flavus is an opportunistic pathogen of oilseed crops such as maize, peanut, cottonseed, and tree nuts and produces carcinogenic secondary metabolites known as aflatoxins during seed colonization. Aflatoxin contamination not only reduces the value of the produce but also is a health hazard to humans and animals. Previously, we observed inhibition of A. flavus aflatoxin biosynthesis upon exposure to the marine bacterium, Vibrio gazogenes (Vg). In this study, we used RNA sequencing to examine the transcriptional profiles of A. flavus treated with both live and heat-inactivated dead Vg and control samples. Fungal biomass, total accumulated aflatoxins, and expression profiles of genes constituting secondary metabolite biosynthetic gene clusters were determined at 24, 30, and 40 h after treatment. Statistically significant reductions in total aflatoxins were detected in Vg-treated samples as compared to control samples at 40 h. But no statistical difference in fungal biomass was observed upon these treatments. The Vg treatments were most effective on aflatoxin biosynthesis as was reflected in significant downregulation of majority of the genes in the aflatoxin gene cluster including the aflatoxin pathway regulator gene, aflR. Along with aflatoxin genes, we also observed significant downregulation in some other secondary metabolite gene clusters including cyclopiazonic acid and aflavarin, suggesting that the treatment may inhibit other secondary metabolites as well. Finally, a weighted gene correlation network analysis identified an upregulation of ten genes that were most strongly associated with Vg-dependent aflatoxin inhibition and provide a novel start-point in understanding the mechanisms that result in this phenomenon.

scholarly journals Aspergillus Volatiles Regulate Aflatoxin Synthesis and Asexual Sporulation in Aspergillus parasiticus

2007 ◽  
Vol 73 (22) ◽  
pp. 7268-7276 ◽  
Author(s):  
Ludmila V. Roze ◽  
Randolph M. Beaudry ◽  
Anna E. Arthur ◽  
Ana M. Calvo ◽  
John E. Linz
Keyword(s):  
Aspergillus Parasiticus ◽  
Primary Source ◽  
Aflatoxin Contamination ◽  
Aflatoxin Biosynthesis ◽  
Transcript Accumulation ◽  
Potential Health ◽  
Asexual Sporulation ◽  
Norsolorinic Acid ◽  
Aflatoxin Accumulation ◽  
Regulatory Effects

ABSTRACT Aspergillus parasiticus is one primary source of aflatoxin contamination in economically important crops. To prevent the potential health and economic impacts of aflatoxin contamination, our goal is to develop practical strategies to reduce aflatoxin synthesis on susceptible crops. One focus is to identify biological and environmental factors that regulate aflatoxin synthesis and to manipulate these factors to control aflatoxin biosynthesis in the field or during crop storage. In the current study, we analyzed the effects of aspergillus volatiles on growth, development, aflatoxin biosynthesis, and promoter activity in the filamentous fungus A. parasiticus. When colonies of Aspergillus nidulans and A. parasiticus were incubated in the same growth chamber, we observed a significant reduction in aflatoxin synthesis and asexual sporulation by A. parasiticus. Analysis of the headspace gases demonstrated that A. nidulans produced much larger quantities of 2-buten-1-ol (CA) and 2-ethyl-1-hexanol (EH) than A. parasiticus. In its pure form, EH inhibited growth and increased aflatoxin accumulation in A. parasiticus at all doses tested; EH also stimulated aflatoxin transcript accumulation. In contrast, CA exerted dose-dependent up-regulatory or down-regulatory effects on aflatoxin accumulation, conidiation, and aflatoxin transcript accumulation. Experiments with reporter strains carrying nor-1 promoter deletions and mutations suggested that the differential effects of CA were mediated through separate regulatory regions in the nor-1 promoter. The potential efficacy of CA as a tool for analysis of transcriptional regulation of aflatoxin biosynthesis is discussed. We also identify a novel, rapid, and reliable method to assess norsolorinic acid accumulation in solid culture using a Chroma Meter CR-300 apparatus.

Culture Conditions Control Expression of the Genes for Aflatoxin and Sterigmatocystin Biosynthesis in Aspergillus parasiticus and A. nidulans

1998 ◽  
Vol 64 (6) ◽  
pp. 2275-2277 ◽  
Author(s):  
Guo Hong Feng ◽  
Thomas J. Leonard
Keyword(s):  
Gene Expression ◽  
High Temperature ◽  
Aspergillus Nidulans ◽  
Expression Pattern ◽  
Polyketide Synthase ◽  
Aspergillus Parasiticus ◽  
Culture Conditions ◽  
Transcript Expression ◽  
Aflatoxin Biosynthesis ◽  
Homologous Genes

ABSTRACT High temperature and nitrate supported gene expression for sterigmatocystin biosynthesis in Aspergillus nidulans; ammonium did not. Homologous genes for aflatoxin biosynthesis inA. parasiticus showed the opposite transcript expression pattern, suggesting that the two mycotoxins are regulated differently. The aflR gene is postulated to require additional genetic elements to effect its own activation by the different culture conditions. A patulin polyketide synthase (PKS) gene was found to be regulated differently than the aflatoxin PKS. Thus, the biosyntheses of structurally similar compounds in these two fungi appear to be regulated very differently.

Resistance to Aflatoxin Contamination in Corn as Influenced by Relative Humidity and Kernel Germination

1996 ◽  
Vol 59 (3) ◽  
pp. 276-281 ◽  
Author(s):  
B. Z. GUO ◽  
J. S. RUSSIN ◽  
R. L. BROWN ◽  
T. E. CLEVELAND ◽  
N. W. WIDSTROM
Keyword(s):  
Relative Humidity ◽  
Aspergillus Flavus ◽  
Aflatoxin B1 ◽  
Resistance Mechanisms ◽  
Aflatoxin Contamination ◽  
Aflatoxin Biosynthesis ◽  
Aflatoxin Accumulation ◽  
Moisture Conditions ◽  
Very High ◽  
Fungus Growth

Kernels of corn population GT-MAS:gk, resistant to aflatoxin B1 production by Aspergillus flavus, and susceptible Pioneer hybrid 3154 were tested for aflatoxin when incubated under different relative humidities (RH). High aflatoxin levels were not detected in either genotype at RH < 91%. Resistance in GT-MAS:gk was consistent across all RH levels (91 to 100%) at which significant aflatoxin accumulation was detected. Aflatoxin levels in GT-MAS:gk averaged about 98% less than those in susceptible Pioneer 3154, which suggests that storage of this or other genotypes with similar resistance mechanisms may be possible under moisture conditions less exacting than are required with susceptible hybrids. Results for fungus growth and sporulation ratings on kernel surfaces were similar to those for aflatoxin levels. When kernels of both genotypes were preincubated 3 days at 100% RH prior to inoculation with A. flavus, germination percentages increased to very high levels compared to those of kernels that were not preincubated. In preincubated kernels aflatoxin levels remained consistently low in GT-MAS:gk but decreased markedly (61%) in Pioneer 3154. When eight susceptible hybrids were evaluated for aflatoxin accumulation in preincubated kernels, seven of these supported significantly lower toxin levels than kernels not subjected to preincubation. Average reduction across hybrids was 83%, and reductions within hybrids ranged from 68 to 96%. Preincubated kernels of one susceptible hybrid (Deltapine G-4666) supported aflatoxin levels comparable to those in resistant GT-MAS:gk. Data suggest that an inhibitor of aflatoxin biosynthesis may be induced during kernel germination. Possible mechanisms for embryo effects on resistance to aflatoxin accumulation are discussed.

Aflatoxin accumulation and kernel infection of maize hybrids inoculated with Aspergillus flavus and Aspergillus parasiticus

2010 ◽  
Vol 3 (1) ◽  
pp. 89-93 ◽  
Author(s):  
G. Windham ◽  
L. Hawkins ◽  
W. Williams
Keyword(s):  
Aspergillus Flavus ◽  
Aspergillus Parasiticus ◽  
Aflatoxin Contamination ◽  
Maize Hybrids ◽  
Maize Germplasm ◽  
Kernel Infection ◽  
Needle Technique ◽  
Eastern Usa ◽  
Aflatoxin Accumulation ◽  
Maize Grain

Over a three year period, we compared aflatoxin accumulation and kernel infection in maize hybrids inoculated with Aspergillus flavus isolate NRRL 3357, A. flavus isolate NRRL 19772, Aspergillus parasiticus isolate NRRL 6111, and all combinations of these isolates. Maize hybrids were inoculated with the Aspergillus strains using the side-needle technique at 7 days after midsilk (50% of the plants had silks emerged). Aspergillus kernel infection and aflatoxin contamination were determined at ca. 63 days after midsilk. A. flavus isolate 3357 induced high levels of aflatoxin contamination in the maize grain which was similar to levels found when this isolate was combined with the other two Aspergillus isolates. Kernel infection levels were higher in one hybrid when a combination of isolates including isolate 3357 was used. A. flavus isolate 3357 has been used to evaluate maize germplasm for aflatoxin resistance in the south-eastern USA for over 30 years. Our studies determined that inoculating plants with A. flavus isolate 3357 alone was sufficient for inducing aflatoxin contamination in grain at our location. A combination of A. flavus isolates which include isolate 3357 might be more effective in increasing levels of kernel infection and could also induce higher levels of aflatoxin at locations that do not favour disease development.

scholarly journals Aflatoxin Biosynthesis Cluster Gene cypA Is Required for G Aflatoxin Formation

2004 ◽  
Vol 70 (11) ◽  
pp. 6518-6524 ◽  
Author(s):  
Kenneth C. Ehrlich ◽  
Perng-Kuang Chang ◽  
Jiujiang Yu ◽  
Peter J. Cotty
Keyword(s):  
Polyketide Synthase ◽  
Aspergillus Parasiticus ◽  
Amino Acid Identity ◽  
Gibberella Zeae ◽  
Aflatoxin Biosynthesis ◽  
P450 Monooxygenase ◽  
Pathway Gene ◽  
Polyketide Synthase Gene ◽  
Aspergillus Nomius ◽  
Cluster Gene

ABSTRACT Aspergillus flavus isolates produce only aflatoxins B1 and B2, while Aspergillus parasiticus and Aspergillus nomius produce aflatoxins B1, B2, G1, and G2. Sequence comparison of the aflatoxin biosynthesis pathway gene cluster upstream from the polyketide synthase gene, pksA, revealed that A. flavus isolates are missing portions of genes (cypA and norB) predicted to encode, respectively, a cytochrome P450 monooxygenase and an aryl alcohol dehydrogenase. Insertional disruption of cypA in A. parasiticus yielded transformants that lack the ability to produce G aflatoxins but not B aflatoxins. The enzyme encoded by cypA has highest amino acid identity to Gibberella zeae Tri4 (38%), a P450 monooxygenase previously shown to be involved in trichodiene epoxidation. The substrate for CypA may be an intermediate formed by oxidative cleavage of the A ring of O-methylsterigmatocystin by OrdA, the P450 monooxygenase required for formation of aflatoxins B1 and B2.

scholarly journals Aspergillus flavus in Soils and Corncobs in South Texas: Implications for Management of Aflatoxins in Corn-Cotton Rotations

Plant Disease ◽  
2004 ◽  
Vol 88 (12) ◽  
pp. 1366-1371 ◽  
Author(s):  
Ramon Jaime-Garcia ◽  
Peter J. Cotty
Keyword(s):  
Aspergillus Flavus ◽  
Rio Grande Valley ◽  
Aflatoxin Contamination ◽  
Soil Samples ◽  
South Texas ◽  
Reduced Tillage ◽  
The North ◽  
Previous Season ◽  
Significant Difference

Aspergillus flavus causes aflatoxin contamination in both cottonseed and corn. Corn-cotton rotations are common in South Texas, where reduced tillage frequently results in long-term residence of corncobs on soil surfaces. Corncobs are colonized by A. flavus either prior to harvest or while in the soil. This study sought to determine the potential of corncobs as sources of inoculum for cotton and corn in South Texas. A. flavus communities in corncob and soil samples were collected during the planting seasons of 2001 to 2003 from 29 fields extending from Calhoun and Victoria Counties in the north to the Rio Grande Valley. In order to assess persistence of A. flavus in corncobs, A. flavus communities in corncobs and soil were contrasted every 2 to 3 months in four fields throughout the 3-year study. To assess seasonal variation, similar contrasts were performed in two fields on a biweekly basis. The results indicate that corncobs are major sources of A. flavus inoculum. Corncobs from the previous season contained, on average, over 190 times more A. flavus propagules than soil from the same field, and 2-year-old corncobs still retained 45 times more propagules than soil. There was no significant difference in the incidence of A. flavus strain S on corncobs and soil. The quantity of A. flavus in corncobs decreased with corncob age (r 2 = 0.54; P = 0.002).

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