scholarly journals Balancing selection for aflatoxin in Aspergillus flavus is maintained through interference competition with, and fungivory by insects

2017 ◽  
Vol 284 (1869) ◽  
pp. 20172408 ◽  
Author(s):  
Milton T. Drott ◽  
Brian P. Lazzaro ◽  
Dan L. Brown ◽  
Ignazio Carbone ◽  
Michael G. Milgroom
Keyword(s):  
Aspergillus Flavus ◽  
Balancing Selection ◽  
Interference Competition ◽  
Fold Increase ◽  
Aflatoxin Production ◽  
Fitness Advantage ◽  
Naturally Occurring ◽  
Selection For ◽  
Single Larva

The role of microbial secondary metabolites in the ecology of the organisms that produce them remains poorly understood. Variation in aflatoxin production by Aspergillus flavus is maintained by balancing selection, but the ecological function and impact on fungal fitness of this compound are unknown. We hypothesize that balancing selection for aflatoxin production in A. flavus is driven by interaction with insects. To test this, we competed naturally occurring aflatoxigenic and non-aflatoxigenic fungal isolates against Drosophila larvae on medium containing 0–1750 ppb aflatoxin, using quantitative PCR to quantify A. flavus DNA as a proxy for fungal fitness. The addition of aflatoxin across this range resulted in a 26-fold increase in fungal fitness. With no added toxin, aflatoxigenic isolates caused higher mortality of Drosophila larvae and had slightly higher fitness than non-aflatoxigenic isolates. Additionally, aflatoxin production increased an average of 1.5-fold in the presence of a single larva and nearly threefold when the fungus was mechanically damaged. We argue that the role of aflatoxin in protection from fungivory is inextricably linked to its role in interference competition. Our results, to our knowledge, provide the first clear evidence of a fitness advantage conferred to A. flavus by aflatoxin when interacting with insects.

scholarly journals Arsenic Removal by Advanced Electrocoagulation Processes: The Role of Oxidants Generated and Kinetic Modeling

Catalysts ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 928
Author(s):  
Micah Flor V. Montefalcon ◽  
Meliton R. Chiong ◽  
Augustus C. Resurreccion ◽  
Sergi Garcia-Segura ◽  
Joey D. Ocon
Keyword(s):  
Kinetic Modeling ◽  
Arsenic Removal ◽  
Fold Increase ◽  
Electrochemical Treatment ◽  
Promising Alternative ◽  
Iron Electrodes ◽  
Removal Capacity ◽  
Naturally Occurring ◽  
Treatment Technologies

Arsenic (As) is a naturally occurring element in the environment that poses significant risks to human health. Several treatment technologies have been successfully used in the treatment of As-contaminated waters. However, limited literature has explored advanced electrocoagulation (EC) processes for As removal. The present study evaluates the As removal performance of electrocoagulation, electrochemical peroxidation (ECP), and photo-assisted electrochemical peroxidation (PECP) technologies at circumneutral pH using electroactive iron electrodes. The influence of As speciation and the role of oxidants in As removal were investigated. We have identified the ECP process to be a promising alternative for the conventional EC with around 4-fold increase in arsenic removal capacity at a competitive cost of 0.0060 $/m3. Results also indicated that the rate of As(III) oxidation at the outset of electrochemical treatment dictates the extent of As removal. Both ECP and PECP processes reached greater than 96% As(III) conversion at 1 C/L and achieved 86% and 96% As removal at 5 C/L, respectively. Finally, the mechanism of As(III) oxidation was evaluated, and results showed that Fe(IV) is the intermediate oxidant generated in advanced EC processes, and the contribution of •OH brought by UV irradiation is insignificant.

scholarly journals Fitness Cost of Aflatoxin Production inAspergillus flavusWhen Competing with Soil Microbes Could Maintain Balancing Selection

mBio ◽  
2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Milton T. Drott ◽  
Tracy Debenport ◽  
Steven A. Higgins ◽  
Daniel H. Buckley ◽  
Michael G. Milgroom
Keyword(s):  
Aspergillus Flavus ◽  
Soil Microbes ◽  
Balancing Selection ◽  
Natural Habitat ◽  
Metabolic Cost ◽  
Aflatoxin Production ◽  
Amplicon Sequencing ◽  
Selective Advantage ◽  
Content Type ◽  
Evolutionary Forces

ABSTRACTSelective forces that maintain the polymorphism for aflatoxigenic and nonaflatoxigenic individuals ofAspergillus flavusare largely unknown. As soils are widely considered the natural habitat ofA. flavus, we hypothesized that aflatoxin production would confer a fitness advantage in the soil environment. To test this hypothesis, we usedA. flavusDNA 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 ofA. 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.IMPORTANCEAflatoxin, produced by the fungusAspergillus 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 ofA. flavusproduce 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 toA. flavusin 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.

scholarly journals Regulation of Morphology, Aflatoxin Production, and Virulence of Aspergillus flavus by the Major Nitrogen Regulatory Gene areA

Toxins ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 718 ◽  
Author(s):  
Opemipo Esther Fasoyin ◽  
Kunlong Yang ◽  
Mengguang Qiu ◽  
Bin Wang ◽  
Sen Wang ◽  
...  
Keyword(s):  
Aspergillus Flavus ◽  
Regulatory Gene ◽  
Nitrogen Sources ◽  
Aflatoxin Production ◽  
Fungal Species ◽  
Complete Medium ◽  
Over Expression ◽  
Oxidative Stresses ◽  
Gata Transcription Factor

Aspergillus flavus is a renowned plant, animal and human pathogen. areA is a global nitrogen regulatory gene of the GATA transcription factor family, shown to be the major nitrogen regulator. In this study, we identified areA in A. flavus and studied its function. The AreA protein contained a signatory zinc finger domain, which is extremely conserved across fungal species. Gene deletion (ΔareA) and over-expression (OE::areA) strains were constructed by homologous recombination to elucidate the role of areA in A. flavus. The ΔareA strain was unable to efficiently utilize secondary nitrogen sources for growth of A. flavus, and it had poorly developed conidiophores, when observed on complete medium, resulting in the production of significantly less conidia than the wild-type strain (WT). Aflatoxin B1 (AFB1) production was reduced in ΔareA compared with the WT strain in most conditions tested, and ΔareA had impaired virulence in peanut seeds. areA also played important roles in the sensitivity of A. flavus to osmotic, cell wall and oxidative stresses. Hence, areA was found to be important for the growth, aflatoxin production and pathogenicity of A. flavus. This work sheds light on the function of areA in the regulation of the nitrogen metabolism of A. flavus, and consequently aims at providing new ways for controlling the crossover pathogen, A. flavus.

scholarly journals The posterior vermis of the cerebellum selectively inhibits 10-Hz sympathetic nerve discharge in anesthetized cats

2009 ◽  
Vol 297 (1) ◽  
pp. R210-R217 ◽  
Author(s):  
Susan M. Barman ◽  
Gerard L. Gebber
Keyword(s):  
Sympathetic Nerve ◽  
Cortical Neurons ◽  
Fold Increase ◽  
Total Power ◽  
Chemical Inactivation ◽  
Naturally Occurring ◽  
Functional Implications ◽  
Frequency Components ◽  
Nerve Discharge

We studied the changes in inferior cardiac sympathetic nerve discharge (SND) and mean arterial pressure (MAP) produced by aspiration or chemical inactivation (muscimol microinjection) of lobule IX (uvula) of the posterior vermis of the cerebellum in baroreceptor-denervated and baroreceptor-innervated cats anesthetized with urethane. Autospectral analysis was used to decompose SND into its frequency components. Special attention was paid to the question of whether the experimental procedures affected the rhythmic (10-Hz and cardiac-related) components of SND. Aspiration or chemical inactivation of lobule IX produced an approximately three-fold increase in the 10-Hz rhythmic component of SND ( P ≤ 0.05) in baroreceptor-denervated cats. Total power (0- to 20-Hz band) was unchanged. Despite the absence of a change in total power in SND, there was a statistically significant increase in MAP. In baroreceptor-innervated cats, neither aspiration nor chemical inactivation of the uvula caused a significant change in cardiac-related or total power in SND or MAP. These results are the first to demonstrate a role of cerebellar cortical neurons of the posterior vermis in regulating the frequency composition of naturally occurring SND. Specifically, these neurons selectively inhibit the 10-Hz rhythm-generating network in baroreceptor-denervated, urethane-anesthetized cats. The functional implications of these findings are discussed.

scholarly journals Function of crzA in Fungal Development and Aflatoxin Production in Aspergillus flavus

Toxins ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 567 ◽  
Author(s):  
Su-Yeon Lim ◽  
Ye-Eun Son ◽  
Dong-Hyun Lee ◽  
Tae-Jin Eom ◽  
Min-Ju Kim ◽  
...  
Keyword(s):  
Aspergillus Flavus ◽  
Fungal Growth ◽  
Wall Stress ◽  
Aflatoxin Production ◽  
Colony Growth ◽  
Cell Wall Stress ◽  
Mutant Strains ◽  
Sclerotial Formation ◽  
Calcineurin Pathway

The calcineurin pathway is an important signaling cascade for growth, sexual development, stress response, and pathogenicity in fungi. In this study, we investigated the function of CrzA, a key transcription factor of the calcineurin pathway, in an aflatoxin-producing fungus Aspergillus flavus (A. flavus). To examine the role of the crzA gene, crzA deletion mutant strains in A. flavus were constructed and their phenotypes, including fungal growth, spore formation, and sclerotial formation, were examined. Absence of crzA results in decreased colony growth, the number of conidia, and sclerocia production. The crzA-deficient mutant strains were more susceptible to osmotic pressure and cell wall stress than control or complemented strains. Moreover, deletion of crzA results in a reduction in aflatoxin production. Taken together, these results demonstrate that CrzA is important for differentiation and mycotoxin production in A. flavus.

scholarly journals Deletion of the Aspergillus flavus Orthologue ofA. nidulans fluGReduces Conidiation and Promotes Production of Sclerotia but Does Not Abolish Aflatoxin Biosynthesis

2012 ◽  
Vol 78 (21) ◽  
pp. 7557-7563 ◽  
Author(s):  
Perng-Kuang Chang ◽  
Leslie L. Scharfenstein ◽  
Brian Mack ◽  
Kenneth C. Ehrlich
Keyword(s):  
Aspergillus Flavus ◽  
Fold Increase ◽  
Developmental Changes ◽  
Asexual Development ◽  
Aflatoxin Biosynthesis ◽  
Content Type ◽  
Fold Reduction ◽  
Sclerotial Formation ◽  
Conidial Development

ABSTRACTThefluGgene is a member of a family of genes required for conidiation and sterigmatocystin production inAspergillus nidulans. We examined the role of theAspergillus flavus fluGorthologue in asexual development and aflatoxin biosynthesis. Deletion offluGinA. flavusyielded strains with an approximately 3-fold reduction in conidiation but a 30-fold increase in sclerotial formation when grown on potato dextrose agar in the dark. The concurrent developmental changes suggest thatA. flavusFluG exerts opposite effects on a mutual signaling pathway for both processes. The altered conidial development was in part attributable to delayed expression ofbrlA, a gene controlling conidiophore formation. Unlike the loss of sterigmatocystin production byA. nidulans fluGdeletion strains, aflatoxin biosynthesis was not affected by thefluGdeletion inA. flavus. InA. nidulans, FluG was recently found to be involved in the formation of dehydroaustinol, a component of a diffusible signal of conidiation. Coculturing experiments did not show a similar diffusible meroterpenoid secondary metabolite produced byA. flavus. These results suggest that the function offluGand the signaling pathways related to conidiation are different in the two related aspergilli.

scholarly journals Contribution of OqxAB Efflux Pump in Selection of Fluoroquinolone-Resistant Klebsiella pneumoniae

2018 ◽  
Vol 2018 ◽  
pp. 1-5 ◽  
Author(s):  
Orsolya Szabo ◽  
Bela Kocsis ◽  
Nikolett Szabo ◽  
Katalin Kristof ◽  
Dora Szabo
Keyword(s):  
Klebsiella Pneumoniae ◽  
Efflux Pump ◽  
Fold Increase ◽  
Fluoroquinolone Resistance ◽  
The Novel ◽  
Initial Exposure ◽  
Selection For ◽  
Tract Infections ◽  
Selection Of

The role of OqxAB efflux pump in Klebsiella pneumoniae was investigated in correlation with ciprofloxacin exposure. K. pneumoniae SE23 and K. pneumoniae SE191 were isolated from urinary tract infections and were analyzed in this study. Each carried oqxAB resistance determinant and exhibited ciprofloxacin MIC of 0.06 and 0.5 mg/L, respectively. Tested strains were initially exposed to their ciprofloxacin MIC values for 24 hours. Later on, the ciprofloxacin exposition has been increased to a daily 1, 2, 4, and to a final 8 mg/L. Total cellular RNA was extracted at 30, 60, 90, and 120 minutes of initial exposure and after every 24 hours. Quantitative reverse-transcriptase PCR was performed from each RNA sample. Mutation in gyrA and parC genes was analyzed in each strain and multilocus sequence typing (MLST) was performed. Ciprofloxacin exposure selected resistant strain from K. pneumoniae SE191; by contrast, K. pneumoniae SE23 was not adjustable to the increasing ciprofloxacin concentrations. During initial exposure, both oqxA and oqxB expression remained low (2−ΔCt = 1-2.03). However, increasing ciprofloxacin promoted oqxB expression as it reached fold increase of 15.8–22.8, while oqxA expression was maintained (2−ΔCt = 2-2.15). An amino acid substitution Ser83Tyr in gyrA was detected in K. pneumoniae SE191, but no additional mutations occurred as consequence to ciprofloxacin exposure. MLST identified K. pneumoniae SE191 as ST274, while K. pneumoniae SE23 belonged to the novel ST2567. Ciprofloxacin concentration-dependent upregulation of oqxAB efflux pump in K. pneumoniae is clonally related and contributes to selection for higher level of fluoroquinolone resistance.

scholarly journals Detection of Aflatoxigenic and Non-Aflatoxigenic Isolates of Aspergillus flavus Isolated From Some Clinical and Environmental Sources by HPLC and PCR Techniques

2018 ◽  
Vol 12 (1) ◽  
pp. 40-48
Author(s):  
Mushtak T.S. Al-Ouqaili ◽  
Mohammed H. Muslih ◽  
Salah M. A. Al-Kubaisi
Keyword(s):  
Aspergillus Flavus ◽  
High Performance ◽  
Target Genes ◽  
High Efficiency ◽  
High Sensitivity ◽  
Aflatoxin Production ◽  
Toxin Production ◽  
Genes Encoding ◽  
Hplc Technique

This study aimed to determine the role of polymerase chain reaction (PCR) and High-performance liquid chromatography (HPLC) technique in the discrimination between aflatoxigenic and non-aflatoxigenic isolates of Aspergillus flavus. The isolates were identified based on macroscopical and microscopical characteristics, and extracted aflatoxin was detected by HPLC technique. Furthermore, DNA was extracted from the all isolates and carried out by PCR to amplify target genes encoding for toxin production (nor-1, ver-1 and aflR). The results showed that the genes (aflR, nor-1) were found in 11 (73%) of isolates, while the (ver-1) gene appeared in 10 (67%) of isolates. Both aflatoxigenic and non-aflatoxigenic isolates were also determined depending on the amplification of gene sites in the targeted DNA. HPLC technique has also used with high efficiency to ensure the aflatoxin-producing isolates and to evaluate the level of aflatoxin B1 production for 15 isolates of A. flavus. Ten isolates were able to produce aflatoxin with rates ranged from 0.78 to 45.03 ppm. PCR technique has proved high efficiency in the differentiation between aflatoxigenic and non-aflatoxigenic isolates of A. flavus. Moreover, aflatoxin production was directly associated with gene appearance and gene detection. Also, HPLC technique is a standard and superb technique in identifying and analyzing aflatoxin with high sensitivity and accuracy.

scholarly journals Genetic Responses and Aflatoxin Inhibition during Co-Culture of Aflatoxigenic and Non-Aflatoxigenic Aspergillus flavus

Toxins ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 794
Author(s):  
Rebecca R. Sweany ◽  
Brian M. Mack ◽  
Geromy G. Moore ◽  
Matthew K. Gilbert ◽  
Jeffrey W. Cary ◽  
...  
Keyword(s):  
Gene Expression ◽  
Aspergillus Flavus ◽  
Gene Clusters ◽  
Aflatoxin Production ◽  
Acid Synthesis ◽  
Aflatoxin Contamination ◽  
Oxidation Reduction ◽  
Or Gene ◽  
Genetic Responses

Aflatoxin is a carcinogenic mycotoxin produced by Aspergillus flavus. Non-aflatoxigenic (Non-tox) A. flavus isolates are deployed in corn fields as biocontrol because they substantially reduce aflatoxin contamination via direct replacement and additionally via direct contact or touch with toxigenic (Tox) isolates and secretion of inhibitory/degradative chemicals. To understand touch inhibition, HPLC analysis and RNA sequencing examined aflatoxin production and gene expression of Non-tox isolate 17 and Tox isolate 53 mono-cultures and during their interaction in co-culture. Aflatoxin production was reduced by 99.7% in 72 h co-cultures. Fewer than expected unique reads were assigned to Tox 53 during co-culture, indicating its growth and/or gene expression was inhibited in response to Non-tox 17. Predicted secreted proteins and genes involved in oxidation/reduction were enriched in Non-tox 17 and co-cultures compared to Tox 53. Five secondary metabolite (SM) gene clusters and kojic acid synthesis genes were upregulated in Non-tox 17 compared to Tox 53 and a few were further upregulated in co-cultures in response to touch. These results suggest Non-tox strains can inhibit growth and aflatoxin gene cluster expression in Tox strains through touch. Additionally, upregulation of other SM genes and redox genes during the biocontrol interaction demonstrates a potential role of inhibitory SMs and antioxidants as additional biocontrol mechanisms and deserves further exploration to improve biocontrol formulations.

Fine structure and properties of defects in naturally occurring silicates and oxides

1990 ◽  
Vol 48 (4) ◽  
pp. 460-461
Author(s):  
David R. Veblen
Keyword(s):  
Chemical Reactions ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Single Chain ◽  
Naturally Occurring ◽  
Resolution Electron ◽  
Fine Structures ◽  
Image Simulations ◽  
Similar Crystal Structure

Extended defects and interfaces control many processes in rock-forming minerals, from chemical reactions to rock deformation. In many cases, it is not the average structure of a defect or interface that is most important, but rather the structure of defect terminations or offsets in an interface. One of the major thrusts of high-resolution electron microscopy in the earth sciences has been to identify the role of defect fine structures in reactions and to determine the structures of such features. This paper will review studies using HREM and image simulations to determine the structures of defects in silicate and oxide minerals and present several examples of the role of defects in mineral chemical reactions. In some cases, the geological occurrence can be used to constrain the diffusional properties of defects.The simplest reactions in minerals involve exsolution (precipitation) of one mineral from another with a similar crystal structure, and pyroxenes (single-chain silicates) provide a good example. Although conventional TEM studies have led to a basic understanding of this sort of phase separation in pyroxenes via spinodal decomposition or nucleation and growth, HREM has provided a much more detailed appreciation of the processes involved.

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