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  • Aspergillus  (29)
  • Aspergillus flavus  (29)
  • 1
    ISSN: 1573-0832
    Keywords: aflatoxin ; Aspergillus flavus ; non-toxigenic O-methylsterigmetocystin ; sterigmetocystin ; nontoxigenic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Non-aflatoxin-producing isolates ofAspergillus flavus from nature and isolates ofA. flavus that had lost their toxigenic trait following laboratory transfer were compared biochemically. After the addition of aflatoxin B1 precursors sterigmatocystin or O-methylsterigmatocystin to whole cell cultures, the non-toxin producing isolates from nature remained non-toxigenic while toxigenicity was restored in the nontoxigenic laboratory strains. Results imply a lack of enzymes needed for biochemical conversions of precursors to aflatoxin B1 in natural non-producers and suppression of these enzymes in the nonproducing laboratory strains.
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  • 2
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; aflatoxin ; cytochemistry ; Gossypium ; ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Cottonseeds having fluorescent fibers were harvested from fields in Arizona and examined utilizing light microscopy and transmission electron microscopy. The occurrence of fluorescent fibers indicated that seeds had been infected by Aspergillus flavus during development. Presence of A. flavus was verified by plating portions of seeds with fluorescent fibers. Hyphae, conidial heads, and conidia were identified readily in differentially-stained cotyledon tissue processed for light microscopy. Utilization of transmission electron microscopy permitted observations on lignified seed coats and cotyledons of mature cottonseeds. Hyphae were located throughout the cotyledon and in the nonlignified layers of the seed coat. The identification of hyphae in cross sections of vessel elements within the seed coat provided ultrastructural evidence supporting the hypothesis that A. flavus may enter seeds via the vascular tissue. Controls for the microscopy studies included observations on cottonseeds with no visual signs of infection and on laboratory-grown cultures of A. flavus. These observations demonstrated that the hyphae localized within fluorescent seeds had features characteristic of A. flavus and that fungal-like structures do not occur within uninfected seeds.
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  • 3
    ISSN: 1573-0832
    Keywords: Versicolorin A ; hemiacetal ; reductase ; Aspergillus ; versicolorin C ; dihydrosterigmatocystin ; aflatoxin G2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Versicolorin A hemiacetal was converted to versicolorin C in cell-free systems fromAspergillus parasiticus. The rate of reaction catalyzed by the 35–70% ammonium sulfate fraction was 0.43 nmol min−1 mg−1 with NADPH as cosubstrate and 0.17 nmol. min−1 mg−1 with NADH at 25°C at pH 7.4. The product from incubation of 17-hdyroxy-16,17-dihydrosterigmatocystin with the 35–70% ammonium sulfate fraction and NADPH was a polar compound which was converted to dihydrosterigmatocystin by 0.4 M HCl. The olar comound is proposed to be the 14,17-hydrated open-chain derivative of dihydrosterigmatocystin. Aflatoxin G2a was also reduced in this system to a polar product tentatively identified as the 13,16-hydrated open-chain derivative of AFG2. The reductase activity may be involved in the formation of reduced intermediates and aflatoxins in cultures ofA. parasiticus.
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  • 4
    ISSN: 1573-0832
    Keywords: Storage fungi ; mycotoxins ; food contaminants ; Aspergillus flavus ; Aspergillus Candidas ; aflatoxin ; rice bran ; raw rice ; parboiled rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Thirty four samples of rice bran, of which 9 were from raw (untreated) rice (RR) and 25 from parboiled rice (PbR) were collected from commercial rice mills in and around Madras and analysed for storage mycoflora and mycotoxins. Fungi of the Aspergillus flavus group were present in 29 of the 34 samples (8 from RR and 21 from PbR) in quantities ranging from 〈1–432 thousand propagules/g, though not always as the dominant mycoflora. Fungal numbers were usually higher in RR than in PbR samples. Five of the 9 RR samples and 6 of the 25 PbR samples were positive for aflatoxins. Among 29 isolates of A. flavus obtained from the bran samples, 16 isolates −6 from RR bran and 10 from PbR bran — were found to be toxigenic in vitro. Some isolates of A. candidus also seemed to produce aflatoxin and other fluorescent substances.
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  • 5
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; Sri Lanka
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The fungal flora of 6 Asian medicinal plants, Aerva lanata (Linn.) Juss. Alyssicarpus vaginalis D.C., Tribulus terrestris Linn. Adhatoda vasica Nees., Centella asciatica (L.) Urb., Cardiospermum halicacabum Linn. was determined. After surface disinfection Aspergillus spp. were most frequently observed. Aspergillus flavus, isolated from Alyssicarpus vaginalis and Aerva lanata produced aflatoxins in culture. Aflatoxin B1 was also detected in a sample of Aerra lanata at a level of 0.5 μg/g. Plant material destined for medicinal use should be stored carefully prior to its use to prevent growth of naturally occurring toxigenic mold fungi.
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  • 6
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; Aflatoxins ; Culture method ; Glass fiber
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A new method for growingAspergllius flavus for experimental studies is presented. The system consists of a humidified vial with a thick septum pierced by a pin on which a glass fiber disc is affixed. The disc contains the test solution and inoculum plus medium. The method has been used to assess the effect of variations in culture conditions on production of aflatoxin B1 (AFB1). The AFB1 level was affected by the amount of medium placed on the disc and type of disc material. The results for different types of glass fiber and quartz discs were compared with AFB1 produced by fungus grown in liquid medium or on paper discs. When compared to a liquid medium culture there was a 15 to 20-fold increase in AFB1 for one type of disc. Incubations with less than 14 µl of medium gave satisfactory results. A crude phosphatidylcholine preparation at a concentration of 0.7% of the medium resulted in a 4-fold increase in AFB1.
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  • 7
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; Elastase ; Elastinolytic ; Metalloproteinase ; Serine proteinase ; Toxigenic fungus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A survey of the distribution of elastinolytic potential among 32 culture collection isolates ofAspergillus flavus, A. oryzae, A. parasiticus, A. sojae, A. nomius, andA. tamarii revealed this character to be highly conserved withinAspergillus SectionFlavi. Furthermore, 144 isolates ofA. flavus from environmental samples from six separate regions of the United States produced elastase on solid medium. Most previously described polymorphisms in elastinolytic potential were attributed to the toxicity of borate buffers. Replacement of borate with HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) resulted in detection of elastase production on solid medium by all tested fungal isolates except two that had been in culture over 50 years. In liquid culture, only isolates ofA. flavus, A. tamarii, andA. oryzae accumulated elastase activity. Although isoelectric focusing revealed only one isoform (pI 9.0) of elastase in these culture filtrates, elastinolytic activity in filtrates was partially inhibited by both 1,10-phenanthrolene (2 mM) and phenylmethylsulfonylfluoride (2 mM), suggesting the presence of both metallo and serine elastinolytic proteinases.
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  • 8
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; aflatoxin ; fungal competition ; barley grain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Colonization of barley grain by Aspergillus flavus and formation of aflatoxin B1 in the presence of Penicillium verrucosum, Fusarium sporotrichioides, and Hyphopichia burtonii were studied over a three-week period in all combinations of 20 or 30 °C and 0.97, 0.95 or 0.90 aw. Grain colonization was assessed initially by observing hyphal extension on the grain surface, using scanning electron microscopy, and then from the proportion of seeds infected and numbers of colony forming units (cfu) formed. Aflatoxin b1 concentrations were determined by enzyme linked immunosorbent assay using a monoclonal antibody. These studies showed that interaction between A. flavus and other fungi in paired culture had different effects on both colonization and aflatoxin formation depending on the species involved and environmental conditions. Germination of A. flavus spores was unaffected by the presence of other species on the grain surface. Subsequently, three principal patterns of A. flavus colonization of barley grain were observed through the incubation period in the presence of other fungal species: (a) colonization unaffected by the presence of other species; (b) colonization initially slower in the presence of other species but later differing little from pure cultures; and (c) colonization adversely affected by the presence of other species. Five main patterns of aflatoxin B1 production were observed relative to pure culture but with no consistent relationship with species, aw, temperature or incubation period; (a) little changed; (b) increased slowly; (c) decreased; (d) enhanced; and (e, f) increased initially but later decreased to (e) the same level as in pure culture or (f) to less than in pure culture. Generally, production of aflatoxin B1 by A. flavus was less than in pure culture but sometimes was changed only slightly by the presence of P. verrucosum, F. sporotrichioides or H. burtonii or was temporarily enhanced.
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  • 9
    ISSN: 1573-0832
    Keywords: Alternaria ; Aspergillus ; cytotoxicity ; Fusarium ; Penicillium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The predominant fungi present in samples of reject and retail red kidney beans were Aspergillus glaucus, Penicillium spp. and Alternaria spp. Together with A. ochraceus, A. flavus, Fusarium spp., and Trichoderma, these isolates from the reject beans were screened for numerous mycotoxins by TLC. The most consistently produced mycotoxins were penicillic acid (from A. ochraceus and Penicillium spp.) and Alternaria toxins (tenuazonic acid and alternariol). A. glaucus strains were tested for cytotoxicity in three tissue culture cell lines with positive results.
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  • 10
    ISSN: 1573-0832
    Keywords: Aspergillus ; Chitin ; Fusarium ; Mosquito ; mycopathogens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract During a short survey of soil and mosquito breeding sites in Lucknow, India for potential mycopathogen from a period of August–October 1996, 11 species of fungi in 5 genera were isolated using live mosquito larvae as host. Aspergillus flavus , A. fumigatus and Fusarium semitectum were the most frequently isolated species. Other fungi recorded were A. niger , A. ochraceus , A. terreus , A. versicolor , Geotrichum candidum , Penicillium verrucosum , Paecilomyces sp. and Fusarium sp. (Liseola/Elegans complex). Insect cell walls are known to contain chitin, so fungal isolates were tested for their chitinase activity on semi synthetic medium containing colloidal chitin. High chitinolytic activities were observed with A. flavus and A. ochraceus. Chitinase producers can be considered as potential pathogens. However, the higher incidence of F. semitectum could not be explained by inability to utilize chitin.
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