Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 803
Filtrar
1.
World J Microbiol Biotechnol ; 35(8): 121, 2019 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-31332590

RESUMO

The economics of bioflocculant production is coupled with the use of a low-cost substrate at appropriate culture conditions. The use of a waste substrate for this purpose offers an additional treatment measure to mitigate environmental pollution. We investigated the growth of Aspergillus flavus and its bioflocculant yield using chicken viscera hydrolysate as the sole media. The effects of culture conditions including time, pH, shaker speed, temperature and inoculum size on bioflocculant production were all investigated and optimised through response surface method based on the central component design (CCD) package of Design Expert. Next, the purified bioflocculant was physically and chemically characterised. Under optimised culture conditions (incubation time 72 h, pH 7, shaker speed 150 rpm, temperature 35 °C and inoculum 4%), 6.75 g/L yield of crude bioflocculant was recorded. The bioflocculant activity was mostly distributed in the cell-free supernatant with optimum efficiency of 91.8% at a dose of 4 mL/100 mL Kaolin suspension. The purified bioflocculant was a glycoprotein consisting of 23.46% protein and 74.5% sugar, including 46% neutral sugar and 2.01% uronic acid. The X-ray photoelectron spectroscopy fundamental analysis of the purified bioflocculant indicated that the mass proportion of C, O and N, were 63.46%, 27.87% and 8.86%, respectively. The bioflocculant is mainly composed of carbonyl, amino, hydroxyl, and amide functional groups. This study for the first time indicates a high potential of bioflocculant yield from chicken viscera at the appropriate culture conditions.


Assuntos
Aspergillus flavus/metabolismo , Meios de Cultura/química , Animais , Galinhas , Glicoproteínas/metabolismo , Concentração de Íons de Hidrogênio , Microscopia Eletrônica de Varredura , Espectroscopia Fotoeletrônica , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura Ambiente , Vísceras
2.
Food Chem ; 293: 472-478, 2019 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-31151636

RESUMO

Water activity (aw) and temperature are two pivotal environmental factors affecting Aspergillus flavus growth and aflatoxin production. Here, we found that AFB1 production on polished rice can occur over a wider range of temperature × aw levels than that on paddies. For fungal growth on polished rice, the optimum conditions were aw 0.92-0.96 and 28-37 °C. The maximum amounts of AFB1 on polished rice was observed at 33 °C and aw 0.96. Compared to 33 °C, all tested genes of A. flavus on polished rice were significantly up-regulated at 25 °C under aw 0.96. The late structural genes of pathway were significantly down-regulated at 37 °C under aw 0.96, although aflR and aflS and most of early structural genes were up-regulated. Compared to aw 0.96, most of pathway genes were significantly down-regulated at aw 0.90 and 0.99 under 33 °C, although two regulatory genes were up-regulated at aw 0.90.


Assuntos
Aflatoxinas/biossíntese , Aspergillus flavus/metabolismo , Aflatoxinas/análise , Aspergillus flavus/genética , Aspergillus flavus/crescimento & desenvolvimento , Cromatografia Líquida de Alta Pressão , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Regulação Fúngica da Expressão Gênica , Oryza/microbiologia , Temperatura Ambiente , Água/química , Água/metabolismo
3.
J Microbiol ; 57(5): 396-404, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31062286

RESUMO

Aspergillus flavus is a saprophytic fungus that contaminates crops with carcinogenic aflatoxin. In the present work, the antifungal effects of volatile organic compounds (VOCs) from Streptomyces alboflavus TD-1 against A. flavus were investigated. VOCs from 8-day-old wheat bran culture of S. alboflavus TD-1 displayed strong inhibitory effects against mycelial growth, sporulation, and conidial germination of A. flavus. Severely misshapen conidia and hyphae of A. flavus were observed by scanning electron microscopy after exposure to VOCs for 6 and 12 h, respectively. Rhodamine 123 staining of mitochondria indicated that mitochondria may be a legitimate antifungal target of the VOCs from S. alboflavus TD-1. Furthermore, the VOCs effectively inhibited aflatoxin B1 production by downregulating genes involved in aflatoxin biosynthesis. Dimethyl trisulfide and benzenamine may play important roles in the suppression of A. flavus growth and production of aflatoxin. The results indicate that VOCs from S. alboflavus TD-1 have tremendous potential to be developed as a useful bio-pesticide for controlling A. flavus.


Assuntos
Aflatoxina B1/biossíntese , Antifúngicos/farmacologia , Aspergillus flavus/crescimento & desenvolvimento , Aspergillus flavus/metabolismo , Agentes de Controle Biológico/farmacologia , Streptomyces/metabolismo , Compostos Orgânicos Voláteis/farmacologia , Aflatoxina B1/genética , Antifúngicos/metabolismo , Agentes de Controle Biológico/metabolismo , Regulação para Baixo/efeitos dos fármacos , Regulação Fúngica da Expressão Gênica , Potencial da Membrana Mitocondrial/efeitos dos fármacos , Mitocôndrias/efeitos dos fármacos , Sulfetos/farmacologia , Compostos Orgânicos Voláteis/metabolismo
4.
Molecules ; 24(9)2019 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-31052538

RESUMO

In the course of investigations on the complex phenomenon of bee decline, Aspergillus flavus was isolated from the haemocoel of worker bees. Observations on the metabolomic profile of this strain showed kojic acid to be the dominant product in cultures on Czapek-Dox broth. However, an accurate review of papers documenting secondary metabolite production in A. flavus also showed that an isomer of kojic acid, identified as 5-(hydroxymethyl)-furan-3-carboxylic acid and named flufuran is reported from this species. The spectroscopic data of kojic acid were almost identical to those reported in the literature for flufuran. This motivated a comparative study of commercial kojic acid and 5-(hydroxymethyl)-furan-3-carboxylic acid, highlighting some differences, for example in the 13C-NMR and UV spectra for the two compounds, indicating that misidentification of the kojic acid as 5-(hydroxymethyl)-furan-3-carboxylic acid has occurred in the past.


Assuntos
Aspergillus flavus/química , Furanos/química , Pironas/química , Aspergillus flavus/metabolismo , Furanos/metabolismo , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Estrutura Molecular , Pironas/metabolismo
5.
Environ Sci Pollut Res Int ; 26(18): 18440-18450, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31049858

RESUMO

In view of the suspected negative impact of synthetic fungicides to the human health, nutritional quality, and non-targeted organisms, the use of plant-based antifungal agents has gained considerable interest to the agri-food industries. The aim of this study was to explore the antifungal and aflatoxin B1 (AFB1) inhibitory activity of chitosan (low molecular weight) encapsulated methyl salicylate. The nanoencapsulation of methyl salicylate (Ne-MS) has been characterized by SEM, FTIR, and XRD analysis. The encapsulation efficiency and loading capacity of Ne-MS ranged between 32-34% and 5-7% respectively. The minimum inhibitory concentration of Ne-MS (1.00 µL/mL) against the growth and aflatoxin B1 production by Aspergillus flavus was found to be lower than the free MS (1.50 µL/mL). Mode of action studies demonstrated that the Ne-MS cause a significant decrease in the ergosterol content, leakage of vital ions (Ca2+, Mg2+, and K+), utilization of different carbon source by the A. flavus. Further, the docking result showed ver1 and omt A gene of AFB1 biosynthesis are the possible molecular site of action of methyl salicylate. The in situ study revealed that Ne-MS had no significant negative impact on the organoleptic properties of the food system (maize) which strengthen its potential as a biorational alternative of synthetic fungicides.


Assuntos
Aflatoxina B1/análise , Aspergillus flavus/efeitos dos fármacos , Fungicidas Industriais/farmacologia , Nanopartículas/química , Salicilatos/farmacologia , Aflatoxina B1/biossíntese , Aspergillus flavus/metabolismo , Fungicidas Industriais/administração & dosagem , Humanos , Testes de Sensibilidade Microbiana , Salicilatos/administração & dosagem , Zea mays/efeitos dos fármacos
6.
Bioresour Technol ; 284: 155-160, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30928827

RESUMO

The aim of the present study was to develop an eco-friendly biological process for the production of 2,5-furan dicarboxylic acid (FDCA) from 5-hydroxy methylfurfuraldehyde (HMF) using microorganisms. Microorganisms were isolated from the soil samples and evaluated for its biotransformation efficiency. Among the isolates, Aspergillus flavus APLS-1 was found to be potent for efficient conversion of HMF to FDCA. The bioconversion parameters were optimized by Box-Behnken design. The optimization resulted in 67% conversion efficiency where 1 g/L HMF (8 mM) was transformed to 0.83 g/L (6.6 mM) FDCA in 14 days at pH6.5 with biomass size of 5.7 g/L and biomass age 60 h. This is the first report on Aspergillus sp., capable of detoxifying HMF and produces FDCA.


Assuntos
Aspergillus flavus/metabolismo , Ácidos Dicarboxílicos/metabolismo , Furanos/metabolismo , Biomassa , Biotransformação
7.
Prep Biochem Biotechnol ; 49(7): 671-678, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30990111

RESUMO

Aspergillus flavus has been regarded as a potential candidate for its production of industrial enzymes, but the details of ß-glucosidase from this strain is very limited. In herein, we first reported a novel ß-glucosidase (AfBglA) with the molecular mass of 94.2 kDa from A. flavus. AfBglA was optimally active at pH 4.5 and 60 °C and is stable between pH 3.5 and 9.0 and at a temperature of up to 55 °C for 30 min remaining more than 90% of its initial activity. It showed an excellent tolerance to Trypsin, Pepsin, Compound Protease, and Flavourzyme and its activity was not inhibited by specific certain cations. AfBglA displayed broad substrate specificity, it acted on all tested pNP-glycosides and barley glucan, indicating this novel ß-glucosidase exhibited a ß-1, 3-1, 4-glucanase activity. Moreover, the AfBglA could effectively hydrolyze the soybean meal suspension into glucose and exhibit a strong tolerance to the inhibition of glucose at a concentration of 20.0 g/L during the saccharification. The maximum amount of the glucose obtained by AfBglA corresponded to 67.0 g/kg soybean meal. All of these properties mentioned above indicated that the AfBglA possibly attractive for food and feed industry and saccharification of cellulolytic materials.


Assuntos
Aspergillus flavus/enzimologia , Glucose/metabolismo , Soja/metabolismo , beta-Glucosidase/metabolismo , Aspergillus flavus/química , Aspergillus flavus/metabolismo , Estabilidade Enzimática , Glicosídeos/metabolismo , Temperatura Alta , Concentração de Íons de Hidrogênio , Hidrólise , Microbiologia Industrial , Especificidade por Substrato , beta-Glucosidase/química , beta-Glucosidase/isolamento & purificação
8.
J Agric Food Chem ; 67(15): 4200-4213, 2019 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-30916945

RESUMO

In Aspergillus, the cyclic adenosine monophosphate (cAMP) signaling modulates asexual development and mycotoxin biosynthesis. Here, we characterize the cyclase-associated protein Cap in the pathogenic fungus Aspergillus flauvs. The cap disruption mutant exhibited dramatic reduction in hyphal growth, conidiation, and spore germination, while an enhanced production of the sclerotia was observed in this mutant. Importantly, the cap gene was found to be important for mycotoxin biosynthesis and virulence. The domain deletion study demonstrated that each domain played an important role for the Cap protein in regulating cAMP/protein kinase A (PKA) signaling, while only P1 and CARP domains were essential for the full function of Cap. The phosphorylation of Cap at S35 was identified in A. flavus, which was found to play a negligible role for the function of Cap. Overall, our results indicated that Cap with multiple domains engages in mycotoxin production and fungal pathogenicity, which could be designed as potential control targets for preventing this fungal pathogen.


Assuntos
Aflatoxinas/biossíntese , Aspergillus flavus/metabolismo , Proteínas Fúngicas/química , Proteínas Fúngicas/metabolismo , Aspergillus flavus/enzimologia , Aspergillus flavus/genética , Aspergillus flavus/patogenicidade , AMP Cíclico/metabolismo , Proteínas Fúngicas/genética , Regulação Fúngica da Expressão Gênica , Doenças das Plantas/microbiologia , Domínios Proteicos , Esporos Fúngicos/enzimologia , Esporos Fúngicos/genética , Esporos Fúngicos/crescimento & desenvolvimento , Esporos Fúngicos/metabolismo , Virulência , Zea mays/microbiologia
9.
Int J Food Microbiol ; 296: 8-13, 2019 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-30825812

RESUMO

Nyjer oil seed cake supports high levels of aflatoxin B1 (AFB1) production. AFB1 is a secondary metabolite of Aspergillus flavus and A. parasiticus, classified as a Class 1A carcinogen. The aim of this study was to determine the effects of temperature (20, 27, and 35 °C) and water activity (0.82, 0.86, 0.90, 0.94, and 0.98 aw) on fungal growth and AFB1 production of A. flavus and A. parasiticus on ground Nyjer seeds over a 30-day incubation period. Linear regression models indicated that both fungal growth and AFB1 production were significantly influenced by water activity of Nyjer seeds and incubation temperature. The two fungi did not grow on Nyjer seeds at 0.82 aw at the three incubation temperatures. The most favorable growth conditions for both fungi were 0.90-0.98 aw at 27 °C or 0.90-0.94 aw at 35 °C. The optimum temperature for AFB1 production was 27 °C for both A. flavus and A. parasiticus (with regression coefficients of 6.01 and 9.11, respectively). Both fungi were likely to produce high levels of AFB1 at 0.90 aw (with regression coefficients of 3.56 for A. flavus and 7.17 for A. parasiticus). Aspergillus flavus only produced AFB1 on seeds with 0.90-0.98 aw at 27 °C (in the range of 203-282 µg/kg) and on seeds with 0.90 aw at 35 °C (212 µg/kg). No detectable AFB1 was produced by this fungus in any other culture conditions that were studied. Aspergillus parasiticus, in contrast, was able to produce AFB1 under all of the growth conditions. At 20 °C, this fungus produced the highest level of AFB1 (212 µg/kg) at high water activity (0.98 aw). At 27 °C, A. parasiticus produced high levels of AFB1 (in the range of 209-265 µg/kg) at a wide range of water activities (0.86-0.98 aw). In the entire study, the highest AFB1 concertation for A. parasiticus was detected on seeds incubated at high temperature (35 °C) and low water activity (0.86 aw). The findings of this study could help optimize the storage conditions of Nyjer oil seeds to reduce aflatoxin contamination.


Assuntos
Aflatoxina B1/biossíntese , Aspergillus flavus/crescimento & desenvolvimento , Aspergillus flavus/metabolismo , Asteraceae/microbiologia , Sementes/microbiologia , Temperatura Alta , Água/análise
10.
Ecotoxicol Environ Saf ; 176: 108-118, 2019 Jul 30.
Artigo em Inglês | MEDLINE | ID: mdl-30925326

RESUMO

Rhizospheric and plant root associated microbes generally play a protective role against arsenic toxicity in rhizosphere. Rhizospheric microbial interaction influences arsenic (As) detoxification/mobilization into crop plants and its level of toxicity and burden. In the present investigation, we have reported a rhizospheric fungi Aspergillus flavus from an As contaminated rice field, which has capability to grow at high As concentration and convert soluble As into As particles. These As particles showed a reduced toxicity to soil dwelling bacteria, fungi, plant and slime mold. It does not disrupt membrane potential, inner/outer membrane integrity and survival of the free N2 fixating bacteria. In arbuscular mycorrhiza like endophytic fungi Piriformospora indica, these As particles does not influence mycelial growth and plant beneficial parameters such as phosphate solubilizing enzyme rAPase secretion and plant root colonization. Similarly, it does not affect plant growth and chlorophyll content negatively in rice plant. However, these As particles showed a poor absorption and mobilization in plant. These As particle also does not affect attachment process and survival of amoeboid cells in slime mold, Dictyostelium discoideum. This study suggests that the process of conversion of physical and chemical properties of arsenic during transformation, decides the toxicity of arsenic particles in the rhizospheric environment. This phenomenon is of environmental significance, not only in reducing arsenic toxicity but also in the survival of healthy living organism in arsenic-contaminated rhizospheric environment.


Assuntos
Arsênico/metabolismo , Arsênico/toxicidade , Microbiota/efeitos dos fármacos , Micorrizas/metabolismo , Oryza/metabolismo , Microbiologia do Solo , Aspergillus flavus/metabolismo , Biotransformação , Oryza/crescimento & desenvolvimento , Oryza/microbiologia , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Raízes de Plantas/microbiologia , Rizosfera , Solo/química , Poluentes do Solo/metabolismo , Poluentes do Solo/toxicidade
11.
J Basic Microbiol ; 59(6): 599-608, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30900741

RESUMO

Aflatoxins are part of fungal secondary metabolites which become serious health, environmental, and economic problems and can cause corruption of many crops and agricultural grains that used as food and feed for human and animal. Aflatoxins mainly produce by Aspergillus spp. especially Aspergillus flavus and Aspergillus parasiticus. The present work aimed to study the effect of nanoencapsulation of chitosan (CS) nanoparticles with two phenolic compounds 1-(2-ethyl,6-heptyl)phenol (EHP) extracted from Cuminum cyminum and 5-ethyl-2-(methoxymethyl)phenol (EMMP) extracted from black pepper on growth and aflatoxins production of A. flavus and A. parasiticus. A. flavus growth was completely inhibited by 0.6 mg/ml of EHP and EMMP as well as A. parasiticus which showed the same minimal inhibition concentration with the first compound and 0.8 mg/ml with the second one. CS nanoparticles inhibited the growth of the tested organisms more than CS especially with A. parasiticus and this potency became much better when nanoencapsulated with the two extracted phenolic compounds. In inhibition of aflatoxins production, EHP reduced the production of aflatoxin B1 and B2 of A. flavus by 68.6% and 69.7%, respectively. In the same manner EMMP reduce the production of the two toxins by 87.3% and 82.6%, respectively. The reduction effect of CS nanoparticles is much more than that of CS as it record in most cases about twofold increase. Nanoencapsulation of CS nanoparticles by the extracted phenolic compounds is much more effective with complete inhibition of aflatoxin B1 of both fungi and aflatoxin G1 of A. parasiticus.


Assuntos
Aflatoxinas/biossíntese , Aspergillus/crescimento & desenvolvimento , Aspergillus/metabolismo , Quitosana/química , Nanopartículas/química , Fenóis/química , Aspergillus/efeitos dos fármacos , Aspergillus flavus/efeitos dos fármacos , Aspergillus flavus/crescimento & desenvolvimento , Aspergillus flavus/metabolismo , Quitosana/farmacologia , Cuminum/química , Estrutura Molecular , Nanopartículas/toxicidade , Fenóis/isolamento & purificação , Fenóis/farmacologia , Piper nigrum/química
12.
Int J Biol Macromol ; 131: 420-434, 2019 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-30831165

RESUMO

Here, we studied the preparation, characterization, anti-aflatoxigenic activity, and molecular mechanism in vitro of chitosan packaging films containing turmeric essential oil (TEO). First, we took the mechanical properties as the evaluation Index, screened for the optimum preparation conditions of packaging films with 1.5 µL/cm2 TEO using single factor and orthogonal experiments, and characterized the film properties. We found that the addition of TEO affected the microcosmic structure of films and advanced water resistance capacity. In addition, we investigated the inhibitory effects of pure chitosan films and packaging films containing 1.5 µL/cm2 or 3.0 µL/cm2 TEO on the growth and conidial formation of Aspergillus flavus (A. flavus, CGMCC 3.4410), as well as the accumulation of aflatoxin over the course of seven days. We found that the packaging films possessed a prominent antifungal activity on A. flavus. Finally, we discuss preliminary results surrounding gene expression of packaging films which inhibit aflatoxin biosynthesis. The expressions levels of 16 genes related to aflatoxin biosynthesis were found to be either completely or almost completely inhibited. Therefore, the addition of the natural antifungal agent TEO in chitosan packaging films represent a remarkable method to significantly promote the development and application of antifungal packaging materials.


Assuntos
Aflatoxinas/antagonistas & inibidores , Antifúngicos/química , Antifúngicos/farmacologia , Quitosana/química , Curcuma/química , Óleos Voláteis/química , Aflatoxinas/biossíntese , Aspergillus flavus/efeitos dos fármacos , Aspergillus flavus/genética , Aspergillus flavus/metabolismo , Materiais Biocompatíveis/química , Materiais Biocompatíveis/farmacologia , Fenômenos Químicos , Embalagem de Alimentos , Regulação Fúngica da Expressão Gênica/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Modelos Biológicos , Peso Molecular , Óleos Voláteis/isolamento & purificação , Permeabilidade , Extratos Vegetais/química , Solubilidade , Análise Espectral , Vapor , Temperatura Ambiente
13.
Mycotoxin Res ; 35(2): 111-128, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30729404

RESUMO

Aflatoxin is a potent toxin produced by Aspergillus flavus Link:Fr, an opportunistic ear-rot pathogen of maize (Zea mays L. subsp. Mays). Prior to the discovery of aflatoxin, A. flavus was considered a minor pathogen and was not a priority for maize breeders or pathologists. Aflatoxin was discovered in England in 1961 following an epidemic in poultry. By the early 1970s, surveys of agricultural commodities in the USA found that maize produced in the Southeast was especially vulnerable to aflatoxin contamination. Aflatoxin contamination was initially treated as a post-harvest issue, but pre-harvest contamination was proven by 1975. Pre-harvest contamination meant that genetically based host-plant resistance was a possible solution. The potential magnitude of the problem became apparent in 1977 when the southeastern US maize crop suffered epidemic aflatoxin contamination. The first experiment demonstrating the heritability of host-plant resistance to aflatoxin accumulation was published in 1978. These events combined to make breeding for reduced aflatoxin contamination both a high priority and a rational breeding objective. This review surveys the early scientific literature in order to place research on the genetics of aflatoxin accumulation in maize into historical context. It tells the story of how multi-disciplinary research began with veterinary diseases of unknown etiology and resulted in host-plant resistance to a previously minor plant pathogen becoming a central public sector breeding objective.


Assuntos
Aflatoxinas/análise , Aspergillus flavus/metabolismo , Resistência à Doença , Contaminação de Alimentos/análise , Doenças das Plantas/prevenção & controle , Venenos/análise , Zea mays/química , Agricultura/história , Aspergillus flavus/crescimento & desenvolvimento , Inglaterra , História do Século XX , História do Século XXI , Estados Unidos , Zea mays/microbiologia
14.
BMC Mol Biol ; 20(1): 4, 2019 02 11.
Artigo em Inglês | MEDLINE | ID: mdl-30744561

RESUMO

BACKGROUND: Woronin bodies are fungal-specific organelles whose formation is derived from peroxisomes. The former are believed to be involved in the regulation of mycotoxins biosynthesis, but not in their damage repair function. The hexagonal peroxisome protein (HexA or Hex1) encoded by hexA gene in Aspergillus is the main and the essential component of the Woronin body. However, little is known about HexA in Aspergillus flavus. RESULTS: In this study, hexA knock-out mutant (ΔhexA) and complementation strain (ΔhexAC) were produced using homologous recombination. The results showed that, ΔhexA and ΔhexAC were successfully constructed. And the data analysis indicated that the colony diameter, stress sensitivity and the sclerotia formation of A. flavus were nearly not affected by the absence of HexA. Yet, the deletion of hexA gene reduced the production of asexual spores and lessened virulence on peanuts and maize seeds markedly. In addition, it was also found that there was a significant decrease of Aflatoxin B1 production in deletion mutant, when compared to wild type. CONCLUSIONS: Therefore, it suggested that the hexA gene has an essential function in conidia production and secondary metabolism in A. flavus. The gene is also believed to be playing an important role in the invasion of A. flavus to the host.


Assuntos
Aflatoxina B1/biossíntese , Aspergillus flavus , Proteínas Fúngicas/fisiologia , Metabolismo Secundário/fisiologia , Arachis/microbiologia , Aspergillus flavus/genética , Aspergillus flavus/crescimento & desenvolvimento , Aspergillus flavus/metabolismo , Aspergillus flavus/patogenicidade , Proteínas Fúngicas/genética , Deleção de Genes , Técnicas de Inativação de Genes , Metabolismo Secundário/genética , Sementes/microbiologia , Esporos Fúngicos/genética , Esporos Fúngicos/crescimento & desenvolvimento , Esporos Fúngicos/metabolismo , Esporos Fúngicos/patogenicidade , Virulência , Zea mays/microbiologia
15.
Appl Spectrosc ; 73(4): 415-423, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30700102

RESUMO

Current methods for detecting aflatoxin contamination of agricultural and food commodities are generally based on wet chemical analyses, which are time-consuming, destructive to test samples, and require skilled personnel to perform, making them impossible for large-scale nondestructive screening and on-site detection. In this study, we utilized visible-near-infrared (Vis-NIR) spectroscopy over the spectral range of 400-2500 nm to detect contamination of commercial, shelled peanut kernels (runner type) with the predominant aflatoxin B1 (AFB1). The artificially contaminated samples were prepared by dropping known amounts of aflatoxin standard dissolved in 50:50 (v/v) methanol/water onto peanut kernel surface to achieve different contamination levels. The partial least squares discriminant analysis (PLS-DA) models established using the full spectra over different ranges achieved good prediction results. The best overall accuracy of 88.57% and 92.86% were obtained using the full spectra when taking 20 and 100 parts per billion (ppb), respectively, as the classification threshold. The random frog (RF) algorithm was used to find the optimal characteristic wavelengths for identifying the surface AFB1-contamination of peanut kernels. Using the optimal spectral variables determined by the RF algorithm, the simplified RF-PLS-DA classification models were established. The better RF-PLS-DA models attained the overall accuracies of 90.00% and 94.29% with the 20 ppb and 100 ppb thresholds, respectively, which were improved compared to using the full spectral variables. Compared to using the full spectral variables, the employed spectral variables of the simplified RF-PLS-DA models were decreased by at least 94.82%. The present study demonstrated that the Vis-NIR spectroscopic technique combined with appropriate chemometric methods could be useful in identifying AFB1 contamination of peanut kernels.


Assuntos
Aflatoxina B1/análise , Arachis/química , Aspergillus flavus/metabolismo , Contaminação de Alimentos , Arachis/microbiologia , Espectroscopia de Luz Próxima ao Infravermelho/métodos
16.
MBio ; 10(1)2019 02 19.
Artigo em Inglês | MEDLINE | ID: mdl-30782658

RESUMO

Selective forces that maintain the polymorphism for aflatoxigenic and nonaflatoxigenic individuals of Aspergillus flavus are largely unknown. As soils are widely considered the natural habitat of A. flavus, we hypothesized that aflatoxin production would confer a fitness advantage in the soil environment. To test this hypothesis, we used A. flavus DNA quantified by quantitative PCR (qPCR) as a proxy for fitness of aflatoxigenic and nonaflatoxigenic field isolates grown in soil microcosms. Contrary to predictions, aflatoxigenic isolates had significantly lower fitness than did nonaflatoxigenic isolates in natural soils across three temperatures (25, 37, and 42°C). The addition of aflatoxin to soils (500 ng/g) had no effect on the growth of A. flavus Amplicon sequencing showed that neither the aflatoxin-producing ability of the fungus nor the addition of aflatoxin had a significant effect on the composition of fungal or bacterial communities in soil. We argue that the fitness disadvantage of aflatoxigenic isolates is most likely explained by the metabolic cost of producing aflatoxin. Coupled with a previous report of a selective advantage of aflatoxin production in the presence of some insects, our findings give an ecological explanation for balancing selection resulting in persistent polymorphisms in aflatoxin production.IMPORTANCE Aflatoxin, produced by the fungus Aspergillus flavus, is an extremely potent hepatotoxin that causes acute toxicosis and cancer, and it incurs hundreds of millions of dollars annually in agricultural losses. Despite the importance of this toxin to humans, it has remained unclear what the fungus gains by producing aflatoxin. In fact, not all strains of A. flavus produce aflatoxin. Previous work has shown an advantage to producing aflatoxin in the presence of some insects. Our current work demonstrates the first evidence of a disadvantage to A. flavus in producing aflatoxin when competing with soil microbes. Together, these opposing evolutionary forces could explain the persistence of both aflatoxigenic and nonaflatoxigenic strains through evolutionary time.


Assuntos
Aflatoxinas/metabolismo , Antibiose , Aspergillus flavus/crescimento & desenvolvimento , Aspergillus flavus/metabolismo , Metabolismo Energético , Venenos/metabolismo , Microbiologia do Solo , Bactérias/crescimento & desenvolvimento , DNA Fúngico/análise , DNA Fúngico/genética , Aptidão Genética , Genética Populacional , Reação em Cadeia da Polimerase em Tempo Real , Temperatura Ambiente
17.
J Agric Food Chem ; 67(4): 1138-1145, 2019 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-30614691

RESUMO

Fungal contamination imposes threats to agriculture and food production and human health. A method to safely and effectively restrict fungal contamination is still needed. Here, we report the effect and mode of action of ( E)-2-hexenal, one of the green leaf volatiles (GLVs), on the spore germination of Aspergillus flavus, which can contaminate a variety of crops. The EC50 value, minimum inhibitory concentration (MIC), and minimum fungicidal concentration (MFC) of ( E)-2-hexenal were 0.26, 1.0, and 4.0 µL/mL, respectively. As observed by scanning electron microscopy (SEM), the surface morphology of A. flavus spores did not change after treatment with the MIC of ( E)-2-hexenal, but the spores were shrunken and depressed upon treatment with the MFC of ( E)-2-hexenal. The MIC and MFC of ( E)-2-hexenal induced evident phosphatidylserine (PS) externalization of A. flavus spores as detected by double staining with Annexin V-FITC and propidium iodide, indicating that early apoptosis was potentially induced. Furthermore, sublethal doses of ( E)-2-hexenal disturbed pyruvate metabolism and reduced the intracellular soluble protein content of A. flavus spores during the early stage of germination, and MIC treatment decreased acetyl-CoA and ATP contents by 65.7 ± 3.7% and 53.9 ± 4.0% ( P < 0.05), respectively. Additionally, the activity of mitochondrial dehydrogenases was dramatically inhibited by 23.8 ± 2.2% ( P < 0.05) at the MIC of ( E)-2-hexenal. Therefore, the disruption of mitochondrial energy metabolism and the induction of early apoptosis are involved in the mechanism of action of ( E)-2-hexenal against A. flavus spore germination.


Assuntos
Aldeídos/farmacologia , Antifúngicos/farmacologia , Aspergillus flavus/efeitos dos fármacos , Esporos Fúngicos/crescimento & desenvolvimento , Trifosfato de Adenosina/metabolismo , Aldeídos/química , Antifúngicos/química , Aspergillus flavus/crescimento & desenvolvimento , Aspergillus flavus/metabolismo , Metabolismo Energético/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Mitocôndrias/efeitos dos fármacos , Mitocôndrias/metabolismo , Esporos Fúngicos/efeitos dos fármacos , Esporos Fúngicos/metabolismo
18.
Microb Pathog ; 128: 281-287, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30633984

RESUMO

Mosquito that accountable for dispersal of dengue fever is Aedes aegypti Linn. and considered to be a chief vector for dengue especially in South Asian countries. Aspergillus flavus is considered to be wild growing green yellow colonies and synthesis highly regulating aflatoxins (B1, B2, G1 and G2) as a secondary metabolite. Mycotoxins of A. flavus showed its efficacy against III and IV instars of Ae. aegypti with more than 90% mortality at the prominent dosage of 2 × 108 conidia/ml. The proximate lethal concentrations (LC50 and LC90) of mycotoxins against third and fourth instars was 2 × 105 and 2 × 107 respectively. Correspondingly, sub-lethal dosage of mycotoxin A. flavus significantly inhibited the level of α- ß-carboxylesterase and SOD activity and upregulated the level of major detoxifying enzymes GST and CYP450. Moreover, sub-lethal dosage also showed higher deterrent and fecundity effects. Gut-histological examination reveals that the A. flavus considerably affected the gut epithelial cells along with the inner gut lumen as compared to the control. The non-target screening of A. flavus against two aquatic predators (A. bouvieri and Tx. splendens) display more than 80% of mortality rate against both the species at the dosage of 2 × 1016 (two-fold-higher dosage used in larval assays). Thus the biosafety assessment suggests that A. flavus display higher toxicity against the non-targets and it is not-recommended to apply it directly to the aquatic habitat of dengue mosquito which shares their living space with other beneficial insects.


Assuntos
Aedes/efeitos dos fármacos , Aspergillus flavus/metabolismo , Dengue/prevenção & controle , Vetores de Doenças , Micotoxinas/toxicidade , Animais , Carboxilesterase/efeitos dos fármacos , Crustáceos/efeitos dos fármacos , Sistema Enzimático do Citocromo P-450/efeitos dos fármacos , Relação Dose-Resposta a Droga , Ensaios Enzimáticos , Feminino , Trato Gastrointestinal/efeitos dos fármacos , Trato Gastrointestinal/patologia , Glutationa Transferase/efeitos dos fármacos , Inseticidas/toxicidade , Larva/efeitos dos fármacos , Dose Letal Mediana , Mortalidade , Mosquitos Vetores/efeitos dos fármacos , Superóxido Dismutase/efeitos dos fármacos
19.
J Sci Food Agric ; 99(7): 3703-3710, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30663055

RESUMO

BACKGROUND: In concomitance with shifts in climate conditions in recent years, an increasingly frequent emergence of Aspergillus flavus and aflatoxins in cereals has been observed. In this study the effects of temperature (15, 23, 30 and 37 °C) and water activity (aw ) (0.85, 0.90, 0.95 and 0.99) on aflatoxin B1 (AFB1 ) production by A. flavus isolate inoculated on hull-less and hulled spelt grains were investigated. RESULTS: The optimal conditions for AFB1 biosynthesis were reached at 30 °C and aw value of 0.99 in the all tested samples (hull-less grains, dehulled spelt grains and hulls). The AFB1 accumulation was significantly higher in hull-less than in dehulled grains, that implicated a protective effect of spelt hulls. The levels of AFB1 were about 10-170 times higher in hulls than in grains. In order to determine the possibility of predicting the occurrence of AFB1 under different storage conditions mathematical models [second order polynomial (SOP) and artificial neural network (ANN)] were applied. CONCLUSION: The achievement of such estimation facilitates further decisions on continuous monitoring of the potential hazard related to AFB1 contamination of stored spelt-based food. The knowledge of the storage temperature and aw effects on the AFB1 content in spelt during the postharvest phase is of great practical importance. © 2019 Society of Chemical Industry.


Assuntos
Aflatoxina B1/análise , Armazenamento de Alimentos/métodos , Triticum/química , Água/análise , Aflatoxina B1/metabolismo , Aspergillus flavus/metabolismo , Contaminação de Alimentos/análise , Sementes/química , Sementes/microbiologia , Temperatura Ambiente , Triticum/microbiologia
20.
Int J Food Microbiol ; 289: 145-153, 2019 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-30243147

RESUMO

Aflatoxins are toxic carcinogens produced by several species of Aspergillus section Flavi, with some aflatoxin producers associated with specific crops. Red chilies (Capsicum spp.) are grown in warm regions that also favor aflatoxin-producers. Aflatoxins in red chilies may result in serious health concerns and severe economic losses. The current study sought to gain insight on causal agents of aflatoxin contamination in red chilies. Naturally contaminated chilies from markets in Nigeria (n = 55) and the United States (US) (n = 169) were examined. The A. flavus L strain was the predominant member of Aspergillus section Flavi (84%) in chilies. Highly toxigenic fungi with S strain morphology were also detected in chilies from both countries (11%), followed by A. tamarii (4.6%) and A. parasiticus (0.4%). Fungi with L morphology produced significantly lower quantities of aflatoxins (mean = 43 µg g-1) compared to S morphology fungi (mean = 667 µg g-1; p < 0.01) in liquid fermentation. Eighty-one percent of S morphology fungi from chilies in US markets produced only B aflatoxins, whereas 20%, all imported from Nigeria, produced both B and G aflatoxins; all S morphology fungi from Nigerian chilies produced both B and G aflatoxins. Multi-gene phylogenetic analyses of partial gene sequences for nitrate reductase (niaD, 2.1 kb) and the aflatoxin pathway transcription factor (aflR, 1.9 kb) resolved Aspergilli recovered from chilies into five highly supported distinct clades: 1) A. parasiticus; 2) A. flavus with either L or S morphology; 3) A. minisclerotigenes; 4) A. aflatoxiformans, and 5) a new lineage. Aspergillus aflatoxiformans and the new lineage produced the highest concentrations of total aflatoxins in chilies, whereas A. flavus L strains produced the least. The results suggest etiology of aflatoxin contamination of chili is complex and may vary with region. Knowledge of causal agents of aflatoxin contamination of chilies will be helpful in developing mitigation strategies to prevent human exposure.


Assuntos
Aflatoxinas/análise , Aspergillus/fisiologia , Capsicum/microbiologia , Microbiologia de Alimentos , Aflatoxinas/genética , Aspergillus/classificação , Aspergillus/genética , Aspergillus flavus/classificação , Aspergillus flavus/genética , Aspergillus flavus/metabolismo , Produtos Agrícolas/microbiologia , Fungos/classificação , Fungos/metabolismo , Humanos , Nigéria , Filogenia , Estados Unidos
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA