scholarly journals Oxygenase Coordination Is Required for Morphological Transition and the Host–Fungus Interaction of Aspergillus flavus

2009 ◽  
Vol 22 (7) ◽  
pp. 882-894 ◽  
Author(s):  
Sigal Horowitz Brown ◽  
James B. Scott ◽  
Jeyanthi Bhaheetharan ◽  
William C. Sharpee ◽  
Lane Milde ◽  
...  
Keyword(s):  
Aspergillus Flavus ◽  
Unsaturated Fatty Acids ◽  
Aflatoxin Production ◽  
Major Effect ◽  
Signal Molecules ◽  
Density Dependent ◽  
Interdependent Network ◽  
Host Fungus ◽  
Lipoxygenase Gene

Oxylipins, a class of oxygenase-derived unsaturated fatty acids, are important signal molecules in many biological systems. Recent characterization of an Aspergillus flavus lipoxygenase gene, lox, revealed its importance in maintaining a density-dependent morphology switch from sclerotia to conidia as population density increased. Here, we present evidence for the involvement of four more oxylipin-generating dioxygenases (PpoA, PpoB, PpoC, and PpoD) in A. flavus density-dependent phenomena and the effects of loss of these genes on aflatoxin production and seed colonization. Although several single mutants showed alterations in the sclerotia-to-conidia switch, the major effect was observed in a strain downregulated for all five oxygenases (invert repeat transgene [IRT] strain IRT4 = ppoA, ppoB, ppoC, ppoD, and lox). In strain IRT4, sclerotia production was increased up to 500-fold whereas conidiation was decreased down to 100-fold and the strain was unable to switch into conidial production. Aflatoxin (AF) production for all mutant strains and the wild type was greatest at low population densities and absent in high populations except for strain IRT4, which consistently produced high levels of the mycotoxin. Growth on host seed by both IRT4 and IRT2 (downregulated in ppoA, ppoB, and ppoD) was marked by decreased conidial but increased AF production. We propose that A. flavus oxygenases and the oxylipins they produce act in a highly interdependent network with some redundancy of biological function. These studies provide substantial evidence for oxylipin-based mechanisms in governing fungus–seed interactions and in regulating a coordinated quorum-sensing mechanism in A. flavus.

Atoxigenic Aspergillus flavus biological control of aflatoxin contamination: what is the mechanism?

2015 ◽  
Vol 8 (2) ◽  
pp. 235-244 ◽  
Author(s):  
K.E. Damann Jr.
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Population Biology ◽  
Aflatoxin Production ◽  
Infection Process ◽  
Aflatoxin Contamination ◽  
Signal Molecules ◽  
Nutrient Competition ◽  
Toxigenic Strain ◽  
Aflatoxin Inhibition

The term ‘competitive exclusion’ involving physical blockage of growth or access of the toxigenic strain to the seed target has been used to describe the mechanism of biological control of aflatoxin contamination. However, recent evidence suggests that a form of intraspecific aflatoxin inhibition requiring growth of the competing strains together during the infection process in such a way that hyphae physically interact or touch is the trigger for preventing induction of aflatoxin synthesis. This direct touch-based inhibition of aflatoxin synthesis is posited to be the mechanistic basis of biological control in this system. Evidence for this idea comes from the published observations that co-culture of toxigenic and atoxigenic strains in a suspended disc system, in which the hyphae physically interact, prevents aflatoxin production. However, growth of the same strains in the same medium in the two compartments of a filter insert plate well system, separating the atoxigenic and toxigenic strains with a 0.4 μm or 3.0 μm filter, allows aflatoxin production approaching that of the toxigenic strain alone. When the strains are mixed and placed in both the insert and the well compartments, the intraspecific aflatoxin inhibition occurs as it did in the suspended disc culture system. This further suggests that neither nutrient competition nor soluble signal molecules, which should pass through the filter, are involved in intraspecific aflatoxin inhibition. When the two strains are separated by a 12 μm filter that would allow some passage of conidia or hyphae between the compartments the aflatoxin synthesis is approximately half that of the toxigenic strain alone. This phenomenon could be termed ‘competitive inclusion’ or ‘competitive phenotype conversion’. Work of others that relates to understanding the phenomenon is discussed, as well as an Aspergillus flavus population biology study from the Louisiana maize agro-ecosystem which has biological control implications.

scholarly journals Characterization of Mating Type Genes in Aspergillus flavus Populations from Two Locations in Kenya

2018 ◽  
Vol 2018 ◽  
pp. 1-6
Author(s):  
Ouko Abigael ◽  
Okoth Sheila ◽  
Amugune Nelson ◽  
Vesa Joutsjoki
Keyword(s):  
Aspergillus Flavus ◽  
Mating Type ◽  
High Mobility ◽  
Aflatoxin Production ◽  
High Mobility Group Protein ◽  
Group Protein ◽  
Mating Type Genes ◽  
Polymerase Chain ◽  
Mat Genes

In this study, the possibility of sexual reproduction in sampled Aspergillus flavus strains was evaluated by assessing the distribution of mating type (MAT) genes, which are known to control sexual character among fungi, for two counties in Kenya. Forty-four isolates from Nandi and Makueni counties were genotyped by MAT using a multiplex polymerase chain reaction assay. The primer pair for the MAT1-1 amplified a 396 base pair (bp) fragment containing an α-box motif, and MAT1-2 primers targeted a 270 bp segment with a high mobility group protein. The MAT1-2 genes dominated in both regions although the frequency was higher in Nandi (75%) than in Makueni (54.17%). There were no MAT1-1 genes sampled in Nandi, and in Makueni their proportion was 15.91%. The percentage of isolates that amplified for both MAT genes in Makueni was 9.09%, while in Nandi it was 11.36%. Currently, use of aggressive aflatoxin non-producing A. flavus strains as biocontrol is the most promising preharvest aflatoxin control strategy in Kenya. However, we address the possibility of introduced biocontrol strains to breed with existing aflatoxin producing strains in nature, which could lead to the generation of A. flavus offspring capable of aflatoxin production while also being aggressive colonizers and possibly increasing the burden of aflatoxin exposure in food.

scholarly journals Aspergillus Goes Viral: Ecological Insights from the Geographical Distribution of the Mycovirome within an Aspergillus flavus Population and Its Possible Correlation with Aflatoxin Biosynthesis

2021 ◽  
Vol 7 (10) ◽  
pp. 833
Author(s):  
Francesca Degola ◽  
Giorgio Spadola ◽  
Marco Forgia ◽  
Massimo Turina ◽  
Lucia Dramis ◽  
...  
Keyword(s):  
Aspergillus Flavus ◽  
Aflatoxin Production ◽  
Fungal Species ◽  
Natural Environments ◽  
The Novel ◽  
Aflatoxin Biosynthesis ◽  
Biological Variables ◽  
Pattern Distribution ◽  
Toxigenic Strains

Microbial multi-level interactions are essential to control the success of spreading and survival of most microbes in natural environments. Phytopathogenic mycotoxigenic fungal species, such as Aspergillus flavus, represent an important issue in food safety. Usually, non-toxigenic strains are exploited for biocontrol strategies to mitigate infections by toxigenic strains. To comprehend all the biological variables involved in the aflatoxin biosynthesis, and to possibly evaluate the interplay between A. flavus toxigenic and non-toxigenic strains during intraspecific biocompetition, the “virological” perspective should be considered. For these reasons, investigations on mycoviruses associated to A. flavus populations inhabiting specific agroecosystems are highly desirable. Here, we provide the first accurate characterization of the novel mycovirome identified within an A. flavus wild population colonizing the maize fields of northern Italy: a selection of A. flavus strains was biologically characterized and subjected to RNAseq analysis, revealing new mycoviruses and a peculiar geographic pattern distribution in addition to a 20% rate of infection. More interestingly, a negative correlation between viral infection and aflatoxin production was found. Results significantly expanded the limited existent data about mycoviruses in wild A. flavus, opening new and intriguing hypotheses about the ecological significance of mycoviruses.

scholarly journals Investigation of the Antifungal and Anti-Aflatoxigenic Potential of Plant-Based Essential Oils against Aspergillus flavus in Peanuts

2020 ◽  
Vol 6 (4) ◽  
pp. 383
Author(s):  
Premila Narayana Achar ◽  
Pham Quyen ◽  
Emmanuel C. Adukwu ◽  
Abhishek Sharma ◽  
Huggins Zephaniah Msimanga ◽  
...  
Keyword(s):  
Essential Oils ◽  
Aspergillus Flavus ◽  
High Performance ◽  
Opportunistic Infections ◽  
Aflatoxin Production ◽  
The United States ◽  
Microscopy Study ◽  
Aspergillus Species ◽  
Gas Chromatography Mass Spectrometry ◽  
Ammonia Vapor

Aspergillus species are known to cause damage to food crops and are associated with opportunistic infections in humans. In the United States, significant losses have been reported in peanut production due to contamination caused by the Aspergillus species. This study evaluated the antifungal effect and anti-aflatoxin activity of selected plant-based essential oils (EOs) against Aspergillus flavus in contaminated peanuts, Tifguard, runner type variety. All fifteen essential oils, tested by the poisoned food technique, inhibited the growth of A. flavus at concentrations ranging between 125 and 4000 ppm. The most effective oils with total clearance of the A. flavus on agar were clove (500 ppm), thyme (1000 ppm), lemongrass, and cinnamon (2000 ppm) EOs. The gas chromatography-mass spectrometry (GC-MS) analysis of clove EO revealed eugenol (83.25%) as a major bioactive constituent. An electron microscopy study revealed that clove EO at 500 ppm caused noticeable morphological and ultrastructural alterations of the somatic and reproductive structures. Using both the ammonia vapor (AV) and coconut milk agar (CMA) methods, we not only detected the presence of an aflatoxigenic form of A. flavus in our contaminated peanuts, but we also observed that aflatoxin production was inhibited by clove EO at concentrations between 500 and 2000 ppm. In addition, we established a correlation between the concentration of clove EO and AFB1 production by reverse-phase high-performance liquid chromatography (HPLC). We demonstrate in our study that clove oil could be a promising natural fungicide for an effective bio-control, non-toxic bio-preservative, and an eco-friendly alternative to synthetic additives against A. flavus in Georgia peanuts.

scholarly journals Analysis of Antioxidant and Antiallergic Active Components Extracted From the Edible Insect Oxya yezoensis

2021 ◽  
Vol 16 (5) ◽  
pp. 1934578X2110233
Author(s):  
Masahiro Saiki ◽  
Naomichi Takemoto ◽  
Maki Nagata ◽  
Masako Matsumoto ◽  
Yhiya Amen ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Phenolic Compounds ◽  
Unsaturated Fatty Acids ◽  
Soluble Fraction ◽  
Total Phenolic ◽  
Key Factors ◽  
Active Components ◽  
Food And Agriculture ◽  
Food And Agriculture Organization

In recent years, entomophagy has attracted increased attention, as it was recommended as a potential source of food by the Food and Agriculture Organization of the United Nations. In Japan, Oxya yezoensisis one of the most widely eaten insect species, but studies of its functionality as a food are limited. In this study, we reported the optimal characterization of the total phenolic compounds in methanolic extract (OME) and different fractions of OME. Additionally, the antioxidant and antiallergic activities of the OME fractions were evaluated. The results showed that the ethyl acetate-soluble fraction of OME has potential antioxidant activity, whereas the n-hexane-soluble fraction showed the strongest inhibition of β-hexosaminidase, which is one of the key factors in allergic reactions. It was concluded that phenolic compounds might contribute to the antioxidant activity while unsaturated fatty acids contribute to the antiallergy activity.

Characterization of Enterococcus faecium mutants resistant to mundticin KS, a class IIa bacteriocin

Microbiology ◽  
2003 ◽  
Vol 149 (10) ◽  
pp. 2901-2908 ◽  
Author(s):  
Youko Sakayori ◽  
Mizuho Muramatsu ◽  
Satoshi Hanada ◽  
Yoichi Kamagata ◽  
Shinichi Kawamoto ◽  
...  
Keyword(s):  
Enterococcus Faecium ◽  
Antimicrobial Agents ◽  
Wild Type Strain ◽  
Unsaturated Fatty Acids ◽  
Class I ◽  
Wild Type ◽  
Food Preservatives ◽  
In The Wild ◽  
Resistant Mutants

The emergence and spread of mutants resistant to bacteriocins would threaten the safety of using bacteriocins as food preservatives. To determine the physiological characteristics of resistant mutants, mutants of Enterococcus faecium resistant to mundticin KS, a class IIa bacteriocin, were isolated. Two types of mutant were found that had different sensitivities to other antimicrobial agents such as nisin (class I) and kanamycin. Both mutants were resistant to mundticin KS even in the absence of Mg2+ ions. The composition of unsaturated fatty acids in the resistant mutants was significantly increased in the presence of mundticin KS. The composition of the phospholipids in the two resistant mutants also differed from those in the wild-type strain. The putative zwitterionic amino-containing phospholipid in both mutants significantly increased, whereas amounts of phosphatidylglycerol and cardiolipin decreased. These changes in membrane structure may influence resistance of enterococci to class IIa and class I bacteriocins.

scholarly journals Characterization of the Maize Chitinase Genes and Their Effect on Aspergillus flavus and Aflatoxin Accumulation Resistance

PLoS ONE ◽  
2015 ◽  
Vol 10 (6) ◽  
pp. e0126185 ◽  
Author(s):  
Leigh K. Hawkins ◽  
J. Erik Mylroie ◽  
Dafne A. Oliveira ◽  
J. Spencer Smith ◽  
Seval Ozkan ◽  
...  
Keyword(s):  
Aspergillus Flavus ◽  
Aflatoxin Accumulation ◽  
Chitinase Genes

Inhibition of Aflatoxin-Producing Fungi by Welsh Onion Extracts

1999 ◽  
Vol 62 (4) ◽  
pp. 414-417 ◽  
Author(s):  
J. J. FAN ◽  
J. H. CHEN
Keyword(s):  
Aspergillus Flavus ◽  
Mycelial Growth ◽  
Ethanol Extract ◽  
Aflatoxin Production ◽  
Inhibitory Effects ◽  
Welsh Onion ◽  
Extract Concentration ◽  
Ph Values ◽  
Ethanol Extracts ◽  
Yeast Extract Sucrose

Welsh onion ethanol extracts were tested for their inhibitory activity against the growth and aflatoxin production of Aspergillus flavus and A. parasiticus. The survival of spores of A. flavus and A. parasiticus depended on both the extract concentration and the exposure time of the spores to the Welsh onion extracts. The mycelial growth of two tested fungi cultured on yeast extract–sucrose broth was completely inhibited in the presence of the Welsh onion ethanol extract at a concentration of 10 mg/ml during 30 days of incubation at 25°C. The extracts added to the cultures also inhibited aflatoxin production at a concentration of 10 mg/ml or permitted only a small amount of aflatoxin production with extract concentration of 5 mg/ml after 2 weeks of incubation. Welsh onion ethanol extracts showed more pronounced inhibitory effects against the two tested aflatoxin-producing fungi than did the same added levels of the preservatives sorbate and propionate at pH values near 6.5.

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