CERES :: Browsing by Author "Magan, Naresh"

Browsing by Author "Magan, Naresh"

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Open Access
Acclimatisation of Fusarium langsethiae, F. poae and F. sporotrichioides to elevated CO2: impact on fungal growth and mycotoxin production on oat-based media
(Elsevier, 2023-03-28) Kahla, Amal; Verheecke-Vaessen, Carol; Delpino-Deelias, Mariluz; Gutierrez-Pozo, Maria; Medina, Angel; Magan, Naresh; Doohan, Fiona
Oats are highly susceptible to infection by Fusarium species, especially F. langsethiae, F. poae and F. sporotrichioides which contaminate the grain with mycotoxins. Climate change is expected to affect fungal colonisation and associated mycotoxin production. The objective of this study was to examine the effect of acclimatisation to elevated CO2 on the growth and mycotoxin production capacity of these fungal species. Strains of F. langsethiae (FL; seven strains), F. poae (FP; two strains) and F. sporotrichioides (FS; one strain) were acclimatised by sub-culturing for 10 generations at either 400 or 1000 ppm CO2 under diurnal temperature conditions. At each sub-culturing, the effect of acclimatisation to elevated CO2 on (a) lag phase prior to growth, (b) growth rate on oat-based media was assessed. Additionally, the production of type A trichothecenes and related toxic secondary metabolites of sub-cultures after 1, 7 and 10 generations were assessed using LC-MS/MS qTRAP. The results showed that Fusarium strains had an increased lag time and growth rate in response to the combined effect of sub-culturing and elevated CO2 levels. T-2 + HT-2 production was affected by elevated CO2 in strain FL4 (7.1-fold increase) and a decrease in strain FL1 (2.0-fold decrease) at the first sub-culturing and FS (1.3-fold decrease) after 7 sub-cultures compared to ambient conditions. The effect of sub-culturing on T-2 + HT-2 production varied depending on the fungal strain. For strain FL4, significantly less T-2 + HT-2 toxins were produced after 10 generations (4.4-fold decrease) as compared to that under elevated CO2 conditions after one sub-culture, and no change was observed under ambient conditions. The FS strain showed significant stimulation of T-2 + HT-2 toxin production after 10 sub-cultured generations (1.1-fold increase) compared to the initial sub-culture of this strain under elevated CO2 conditions. The production of other toxic secondary metabolites was generally not impacted by elevated CO2 conditions or by sub-culture for 10 generations, with the exceptions of FL1 and FP1. FL1 produced significantly more neosolaniol after 10 generations, when compared to those after 1 and 7, regardless of the CO2 conditions. For FP1, elevated CO2 significantly triggered beauvericin production after an initial sub-culture when compared to ambient conditions at the same sub-culture stage (29-fold). FP1 acclimatisation to elevated CO2 led to a decrease of beauvericin production after 10 generations when compared to 1 (6-fold). In contrast, sub-culturing for 10 generations compared to 1 under ambient CO2 conditions resulted in an increase in this toxin (12-fold).
Open Access
Advances in molecular and genomic research to safeguard food and feed supply from aflatoxin contamination
(Wageningen Academic Publishers, 2018-02-23) Bhatnagar, D; Rajasekaran, K; Gilbert, M; Cary, J. W.; Magan, Naresh
Worldwide recognition that aflatoxin contamination of agricultural commodities by the fungus Aspergillus flavus is a global problem has significantly benefitted from global collaboration for understanding the contaminating fungus, as well as for developing and implementing solutions against the contamination. The effort to address this serious food and feed safety issue has led to a detailed understanding of the taxonomy, ecology, physiology, genomics and evolution of A. flavus, as well as strategies to reduce or control pre-harvest aflatoxin contamination, including (1) biological control, using atoxigenic aspergilli, (2) proteomic and genomic analyses for identifying resistance factors in maize as potential breeding markers to enable development of resistant maize lines, and (3) enhancing host-resistance by bioengineering of susceptible crops, such as cotton, maize, peanut and tree nuts. A post-harvest measure to prevent the occurrence of aflatoxin contamination in storage is also an important component for reducing exposure of populations worldwide to aflatoxins in food and feed supplies. The effect of environmental changes on aflatoxin contamination levels has recently become an important aspect for study to anticipate future contamination levels. The ability of A. flavus to produce dozens of secondary metabolites, in addition to aflatoxins, has created a new avenue of research for understanding the role these metabolites play in the survival and biodiversity of this fungus. The understanding of A. flavus, the aflatoxin contamination problem, and control measures to prevent the contamination has become a unique example for an integrated approach to safeguard global food and feed safety.
Open Access
Alternaria in food: Ecophysiology, mycotoxin production and toxicology
(Hangug Gynnhaghoi, 2016-06-30) Lee, Hyang Burm; Patriarca, Andrea; Magan, Naresh
Alternaria species are common saprophytes or pathogens of a wide range of plants pre- and post-harvest. This review considers the relative importance of Alternaria species, their ecology, competitiveness, production of mycotoxins and the prevalence of the predominant mycotoxins in different food products. The available toxicity data on these toxins and the potential future impacts of Alternaria species and their toxicity in food products pre- and post-harvest are discussed. The growth of Alternaria species is influenced by interacting abiotic factors, especially water activity (a w ), temperature and pH. The boundary conditions which allow growth and toxin production have been identified in relation to different matrices including cereal grain, sorghum, cottonseed, tomato, and soya beans. The competitiveness of Alternaria species is related to their water stress tolerance, hydrolytic enzyme production and ability to produce mycotoxins. The relationship between A. tenuissima and other phyllosphere fungi has been examined and the relative competitiveness determined using both an Index of Dominance (I D ) and the Niche Overlap Index (NOI) based on carbon-utilisation patterns. The toxicology of some of the Alternaria mycotoxins have been studied; however, some data are still lacking. The isolation of Alternaria toxins in different food products including processed products is reviewed. The future implications of Alternaria colonization/infection and the role of their mycotoxins in food production chains pre- and post-harvest are discussed.
Open Access
Alternaria in food: Ecophysiology, mycotoxin production and toxicology- Erratum
(Hangug Gynnhaghoi, 2015-09-01) Lee, Hyang Burm; Patriarca, Andrea; Magan, Naresh
Open Access
Applications of volatile fingerprint sensor arrays for rapid detection of environmental contaminants
(Cranfield University, 2005-03) Canhoto, Olinda; Aldred, David; Magan, Naresh
The electronic nose (e-nose) technology has rapidly evolved in the past decade with a range of applications in the food industry, medical diagnosis, and recently environmental monitoring. This is the first time that this technology has been examined in detail for a range of specific environmental applications including: detection of low concentrations of bacterial, fungal and heavy metal contaminants in potable water; analyses of changes in the microbial activity of soil samples amended with heavy metals; and the detection of fungal contaminants in paper samples from library material. In some studies comparisons between different e-nose systems has also been carried out. The e-nose system based on a conducting polymer (CP) sensor array Bloodhound (BH114) was able to detect different bacterial species (Escherichia coli, Pseudomonas aeruginosa and Enterobacter aerogenes), initially inoculated in tap, reverse osmosis and bottled water with a concentration of 102 cells mL-1, after 24 hrs incubation. In the presence of low concentrations (0.5 ppm) of a mixture of heavy metal ions including cadmium, lead and zinc, the volatile pattern produced by the bacterial species was discriminated from that where no metal was added, probably due to a change in the microbial metabolism. The Bloodhound e-nose system was also used to detect fungal spores of Aspergillus fumigatus, Fusarium culmorum and a Penicillium species, inoculated in water samples. The initial concentrations were 102 – 105 spores mL-1. Good discrimination was observed between the control samples after 24 hrs incubation at 25oC. After 48 hrs incubation, it was possible to differentiate between the various spore concentrations present in water samples. Good reproducibility was achieved as results from different days were consistent and data could be pooled and combined for analysis. A comparative study was performed with three e-nose instruments, two of them had CP sensor arrays (Bloodhound (BH-114); Neotronics (eNOSE 4000), and the third was a metal oxide (MO) sensor-based system, the NST 3220. The experiments carried out with the CP based-systems showed similar results when analysing water samples contaminated with 104 and 102 bacterial cells mL-1 after 24 hrs incubation. Both CP and MO based e-nose systems could differentiate control water samples from those contaminated with both bacteria and fungal spores. GC-SPME analyses confirmed the results obtained with the e-nose system of metal ions and bacterial cells in water samples. At-line studies were performed with the MO array-based system (NST 3220), for the detection of contamination episodes. E. coli and P. aeruginosa cells were used as contamination agents for tap and reverse osmosis sterile water, in two concentration levels, 102 and 106 cells mL-1. The samples collected downstream in a simulated watercourse, were analysed by the e-nose over a period of 1-2 hrs. The results suggested the potential of this technique to monitor episodes of bacterial cells at a low concentration in water samples. Experiments performed in soil samples artificially and naturally contaminated with heavy metal ions were analysed with the MO-based e-nose system. Results indicated that for artificially contaminated soil samples, after 40 days incubation the control samples could be discriminated from those containing 3 and 100 ppm of metal ions. For naturally contaminated soils, the sensor array was only able to separate samples containing a high concentrations of metal ions. Headspace analysis of cellulose-based agar showed good discrimination between Aspergillus terreus, A. hollandicus and Eurotium chevallieri, after 20 hrs incubation at 25oC. An increase in the incubation period to 40 hrs resulted in better separation between the control and fungal treatments. In situ studies performed on paper samples suggested that the e-nose was able to discriminate between control samples and paper inoculated with 103 fungal spores mL-1. The substrate was a determinant factor in the headspace analysis of microbial species. It was shown that the same fungal species produced different volatile profiles according to the growth substrate.
Open Access
Aspergillus species and mycotoxins: occurrence and importance in major food commodities
(Elsevier, 2018-05-18) Taniwaki, Marta Hiromi; Pitt, John I; Magan, Naresh
Aspergillus species produce important mycotoxins, in particular aflatoxins, produced by A. flavus and related species, and ochratoxin A, produced by A. ochraceus and related species and also A. carbonarius and (less commonly) A. niger. In this review we briefly discuss the distribution of toxigenic Aspergillus species in nuts, coffee and cocoa beans, dried fruits, grapes, maize, rice and small grains. Future perspectives of distribution of Aspergillus species in foods are briefly discussed taking into account the impacts of climate change and the resilience of these mycotoxigenic species.
Open Access
Assessment of intraspecies variability in fungal growth initiation of Aspergillus flavus and aflatoxin B1 production under static and changing temperature levels using different initial conidial inoculum levels
(Elsevier, 2018-02-16) Aldars-García, Laila; Marín, Sonia; Sanchis, Vicente; Magan, Naresh; Medina-Vayá, Ángel
Intraspecies variability in fungal growth and mycotoxin production has important implications for food safety. Using the Bioscreen C we have examined spectrophotometrically intraspecies variability of A. flavus using 10 isolates under different environments, including temperature shifts, in terms of growth and aflatoxin B1 (AFB1) production. Five high and five low AFB1 producers were examined. The study was conducted at 5 isothermal conditions (from 15 to 37 °C) and 4 dynamic scenarios (between 15 and 30 °C). The experiments were carried out in a semisolid YES medium at 0.92 aw and two inoculum levels, 102 and 103 spores/mL. The Time to Detection (TTD) of growth initiation was determined and modelled as a function of temperature through a polynomial equation and the model was used to predict TTD under temperature upshifts conditions using a novel approach. The results obtained in this study have shown that a model can be developed to describe the effect of temperature upshifts on the TTD for all the studied isolates and inoculum levels. Isolate variability increased as the growth conditions became more stressful and with a lower inoculum level. Inoculum level affected the intraspecies variability but not the repeatability of the experiments. In dynamic conditions, isolate responses depended both on the temperature shift and, predominantly, the final temperature level. AFB1 production was highly variable among the isolates and greatly depended on temperature (optimum temperature at 30–35 °C) and inoculum levels, with often higher production with lower inoculum. This suggests that, from an ecological point of view, the potential isolate variability and interaction with dynamic conditions should be taken into account in developing strategies to control growth and predicting mycotoxin risks by mycotoxigenic fungi.
Open Access
Assessment of occupational exposure to gasoline vapour at petrol stations
(Cranfield University, 2016-01) Alyami, Ahmed Rashid; Crump, Derrick; Walton, Christopher; Magan, Naresh; Salama, Khaled
Petrol station attendants’ exposure to gasoline vapours while refuelling vehicles has raised health concerns, especially in tropical countries like Saudi Arabia. This is due to the increase of gasoline vaporisation by the high temperatures and related weather conditions. This represents an increase risk of inhaling more vapours than its counterpart temperate countries. Furthermore, exposure during extended working hours (12 hrs shifts), with no vapour recovery system and the handling of gasoline containing a high percentage of volumes of toxic substances (e.g. BTEXs) have not been adequately addressed previously in Saudi Arabia. Therefore, this study was designed and carried out to investigate the validity of this concern by assessing and quantifying full shift exposures to gasoline vapours during the petrol filling process. Different exposure assessment methodologies were employed and evaluated for their suitability. The study assessed the exposures of 41 attendants via passive, active, and direct reading methods at twelve petrol stations with both high and low sales in the Eastern Province of Saudi Arabia. The study was conducted during the winter and summer months to test the seasonal variation of the pattern of exposure. The effects of the quantity of gasoline sold, the locations of the stations, weather variations (e.g. wind speed, temperature, and humidity) were tested. A purpose built mini-weather stations and modified thermometres were utilized to accurately monitor the prevailing weather conditions. Forward-looking infrared (FLIR) thermal image cameras were utilised to visualise the size and movement behaviour of the vapour plumes during petrol refuelling. Furthermore, analytical lab trials were carried out to characterise the gasoline vapour component under different temperatures. These were used to propose a new OEL. The geometric means of the personal passive results for BTEX and MTBE (0.18 ppm, 0.24 ppm, 0.09 ppm, 0.18 ppm, 1.57 ppm, respectively) were found to be relatively higher than those reported previously for Europe and North America. These results are discussed in the context of the impact that such exposure will have on people involved in this industry in petrol stations in Saudi Arabia.
Open Access
Assessment of the effect of Satureja montana and Origanum virens essential oils on Aspergillus flavus growth and aflatoxin production at different water activities
(MDPI, 2020-02-25) García-Díaz, Marta; Gil-Serna, Jessica; Patiño, Belén; García-Cela, Esther; Magan, Naresh; Medina, Angel
Aflatoxin contamination of foodstuffs poses a serious risk to food security, and it is essential to search for new control methods to prevent these toxins entering the food chain. Several essential oils are able to reduce the growth and mycotoxin biosynthesis of toxigenic species, although their efficiency is strongly influenced by the environmental conditions. In this work, the effectiveness of Satureja montana and Origanum virens essential oils to control Aspergillus flavus growth was evaluated under three water activity levels (0.94, 0.96 and 0.98 aw) using a Bioscreen C, a rapid in vitro spectrophotometric technique. The aflatoxin concentrations at all conditions tested were determined by HPLC-FLD. Aspergillus flavus growth was delayed by both essential oil treatments. However, only S. montana essential oil was able to significantly affect aflatoxin production, although the inhibition percentages widely differed among water activities. The most significant reduction was observed at 0.96 aw, which is coincident with the conditions in which A. flavus reached the highest levels of aflatoxin production. On the contrary, the treatment with S. montana essential oil was not effective in significantly reducing aflatoxin production at 0.94 aw. Therefore, it is important to study the interaction of the new control compounds with environmental factors before their application in food matrices, and in vitro ecophysiological studies are a good option since they provide accurate and rapid results.
Open Access
Bacteria in heavy metal contaminated soil: diversity, tolerance and use in remediation
(Cranfield University, 2010) Pires, Carlos; Magan, Naresh; Castro, Paula
The objectives of this project were to determine the bacterial diversity in a heavily contaminated metal region of Portugal. Both traditional and molecular based methods were used to identify tolerant strains and species. The most tolerant species were subsequently identified and utilized for examining the potential for using them to immobilize specific metals from contaminated waste streams by comparing different support materials. Heterotrophic bacterial populations were isolated and characterized from a contaminated industrial area in Northern Portugal. In a first sampling, 278 strains were isolated in different solid media. To assess the diversity of this ecological site and to select representative strains, the isolates were screened by using Random Amplified Polymorphic DNA (RAPD)-PCR profiles. Phenotypic characterization, phylogenetic analysis by sequencing the 16S rRNA genes and metal tolerance tests with zinc (Zn), cadmium (Cd) and arsenic (As) were performed with the selected strains. Recovered gram-positive isolates were related to class Actinobacteria and Bacilli. The majority of the isolates were related to genera Microbacterium and Bacillus. Strains from the genus Arthrobacter were also well represented. 16S rRNA gene sequence similarity of the gram-negative isolates showed that they were related to classes γ-Proteobacteria, ß-Proteobacteria, a-Proteobacteria and Flavobacteria. The most frequently isolated taxa were γ-Proteobacteria, related with the genus Pseudomonas, where a large number of isolates were clustered. These genera are common in metal contaminated environments. Many of the strains (approx. 17) had a high level of tolerance to the heavy metals tested. A total of 13 isolates were not able to grow when metals were present. In a second sampling the soil rhizosphere was screened for bacterial populations, using metal-based selective media for isolation. About 42 strains were recovered when metal supplemented media was used. The gram-positive population were predominantly Bacilli and Actinobacteria members. Bacillus, Microbacterium and Arthrobacter were the most common gram-positive genera. Gram-negative genera were from the same classes as in the first sampling however Sphingobacteria was present. γ-Proteobacteria and ß-Proteobacteria were the most common taxa. The isolates were shown to be very resistant to Zn and As, with about half of the isolates able to grow with Cd present. Interestingly, no strains could grow in the presence of metal mixtures. Despite the number of strains recovered in both samplings the majority of the isolates were clustered within a very small number of genera. During the sampling periods two strains showing low similarity to other bacteria were isolated. These strains were characterized and studied in detail justifying their classification as representing two novel species of the genus Chryseobacterium. The names proposed for these organisms are Chryseobacterium palustre sp. nov. (type strain 3A10[type strain) ) and Chryseobacterium humi sp. nov. (type strain ECP37[type strain] ). Three isolates 1C2, 1ZP4 and EC30 belonging to genera Cupriavidus, Sphingobacterium and Alcaligenes respectively, showing high tolerance to heavy metals, were selected for further study in immobilised systems for Zn and Cd removal. In most cases, matrices (alginate, pectate and a synthetic cross-linked polymer) with immobilised bacteria showed better metal removal. 1C2, a strain belonging to the Cupriavidus genera, was able to increased the removal of Zn; EC30, a bacteria related to Alcaligenes, was the most promising candidate for Cd removal, especially when combined with the synthetic polymer. Removal of metals as single or in binary mixtures was also assessed. Cd removal was most effective when single metal solutions were tested using immobilised bacteria and examining metal matrixes. Based on the strains used and the matrices tested, best results were obtained for removal of Zn from binary mixtures with Cd. Potential exists for further studies to exploit these bacterial strain to develop effective bioremediation approaches for the removal of heavy metals from waste water streams.
Open Access
Biocontrol of mycotoxins: dynamics and mechanisms of action
(Elsevier, 2017-09-18) Medina-Vayá, Ángel; Mohale, Sejakhosi; Samsudin, Nik Iskandar Putra; Rodriguez-Sixtos, Alicia; Rodriguez, Alicia; Magan, Naresh
This paper discusses the relationship between biocontrol agents (BCAs) and mycotoxigenic fungi and mycotoxin control. In most cases BCAs are examined for control of growth of fungal pathogens and disease symptoms. However, for mycotoxin control the approach and focus needs to be different. The mechanism of action and the inoculum dose necessary for control of toxin production by Aspegillus, Penicillium and Fusarium species may be different from that for traditional fungal plant pathogens. The mechanisms of action, the relative inoculum potential and the impact that interacting environmental conditions have on control of key components of the life cycle of mycotoxigenic fungi are considered. The practical aspects of production and formulation hurdles are discussed and potential future approaches and strategies which may need to be considered for more effective biocontrol of mycotoxigenic fungi and mycotoxins are presented.
Open Access
Biodegradation of mixtures of pesticides by bacteria and white rot fungi
(Cranfield University, 2009-04) Gouma, Sofia; Magan, Naresh; Goumas, D.
The objective of this study was to examine the potential for degradation of mixtures of pesticides (chlorpyrifos, linuron, metribuzin) by a range of bacteria and fungi and to relate this capability to enzyme production and quantify the rates of degradation of the components of the mixture of xenobiotic compounds. Overall, although bacteria (19 Bacillus and 4 Pseudomonas species) exhibited tolerance to the individual and micture of pesticides actual degradation was not evident. Five species of white rot fungi were grown on minimal salts agar plates amended with 0, 10 and 30 mg L-1 of chlorpyrifos, linuron and metribuzin, individually and as a mixture with a total concentration 15 and 30 mg L-1. Four of these, T. versicolor, P. gigatea, P.coccineus and P.ostreatus, exhibited very good tolerance to the pesticides. They were also grown on a nutritionally poor soil extract agar amended with a mixture of the pesticides at different concentrations (0-70 mg L-1). Subsequently, the ability of T. versicolor, P. gigatea, P. coccineus to degrade lignin and production of laccase in the presence of mixture of the pesticides was examined as well as their capacity to degrade the pesticide mixture at different concentrations (0-50 mg L-1) in soil extract broth was quantified using HPLC. This showed that only T.versicolor had the ability to degrade linuron, after three weeks incubation although all tested species produced laccase. Subsequently, the temporal degradation rates of T.versicolor was examined in relation to temporal degradation of a mixture of the pesticides chlorpyrifos, linuron and metribuzin with total concentrations 0-50 mg L-1 and the temporal laccase production was quantified over a six week period in relation to ionic and non-ionic water potential stress (-2.8 MPa). These studies showed that the test isolate had the ability to produce very high levels of laccase at -2.8 MPa water potential adjusted non-ionically by using glycerol and quite lower levels in soil extract broth without stress while T.versicolor did not produce laccase at -2.8 MPa when the medium was modified ionically. Finally, T.versicolor was able to degrade the pesticide linuron in all tested water regimes, after five weeks incubation, regardless of the concentration of the mixture. In contrast, about 50% of the metribuzin was degraded, only at at -2.8 MPa water potential adjusted non-ionically with glycerol. Chlorpyrifos and its main metabolite TCP were not detected, possibly, due to a combination of hydrolysis, photolysis and volatilization degradation. The capacity of T.versicolor to degrade linuron in mixtures of pesticides and the production of high levels of laccase, in a nutritionally poor soil extract broth, even under water stress suggests potential application of this fungus in bioremediation.
Open Access
Biodiversity of mycotoxigenic aspergillus species in Egyptian peanuts and strategies for minimizing aflatoxin contamination
(Cranfield University, 2010-12) Sultan, Yousef Yasseen Abdel-Rahmin; Magan, Naresh
Peanuts are an important crop grown in Egypt for either local consumption or export to European markets. The present study examined the importance of mycotoxigenic Aspergilli in Egyptian peanuts from five different regions (Alexandria, El-Beheira, El- Daqahliya, El-Sharqiya, Asyut) in two seasons (2007, 2008). This led to consideration of different potential strategies to control aflatoxigenic A. flavus strains and associated aflatoxin contamination of peanuts. The most common species in peanuts were from Aspergillus section Flavi, Aspergillus section Nigri and Aspergillus section Circumdati. Both qualitative (coconut cream agar) and quantitative analyses (HPLC) were used to analyse the potential mycotoxin production by strains isolated from peanuts. Of a total of 88 Aspergillus section Flavi strains examined, 90% were aflatoxigenic. Cont/d.
Open Access
Bioremediation of the pesticides Dieldrin, Simazine, Trifluralin using tropical and temperate white-rot fungi
(Cranfield University, 1997-08) Elyassi, Ali; Magan, Naresh
The natural breakdown of three pesticides on the UK Red Lis~ dieldrin~ simazine and trifluralin in water and soil varied with environmental conditions. In both sterile and unsterile water trifluralin was degraded to some extent at 20 and 30°C. In contras~ dieldrin and simazine were stable over the 42 days incubation period. A gradient HPLC method was developed for the simultaneous quantification of the three pesticides in soil. In field capacity soil mixtures of the three pesticides (5 and 10 ppm) showed a similar stability with limited degradation at 20°C but increased rates of degradation at 30°C. At the higher concentration the pesticides naturally degraded at a slower rate. Simazine and trifluralin degradation was significantly enhanced with increasing temperature from 20 to 30°C. Water potential (field capacity~ -0.065 MPa~ and - 0.28 MPa) had little effect on the natural breakdown rate of dieldrin. Simazine showed a greater breakdown in the mid-wetness soil~ while trifluralin was degraded rapidly in the field capacity soil, but not at all in the driest treatment over the 70 day experimental period. In vitro studies on solid agar media overlayed with cellophane showed that of four fungi examined~ Trametes cingulata, Trametes socotrana (tropical species) and Phanerochaete chrysosporium and Polystictus versicolor (temperate species) all except P.chrysosporium were able to grow in the presence of 5 ppm of any of the three pesticides at 20 and 30°C, with the latter only growing at 30°C. At 10 ppm concentration P. chrysosporium did not grow, regardless of temperature or time of incubation (up to 56 days). HPLC was used to quantify the temporal rates of degradation in the solid agar media and this showed that P. versicolor and T. socotrana were very effective at breaking down the three pesticides, at 20 and 30°C. The chosen fungi were grown on chopped straw as a carrier and incorporated into soil microcosms in the ratio of 1:10 containing mixtures of the three pesticides (5, 10 ppm) at 20 and 30°C, and subsequently under different water potential regimes at 20°C only, over periods of 70 days. P. versicolor alone significantly increased breakdown of 5 ppm dieldrin by 26% over untreated controls, while simazine breakdown was increased by 16%. However, for simazine at 30°C there was no difference between temporal rates of natural breakdown and those containing fungal inocula, regardless of concentration. With 5 ppm trifluralin, a maximum breakdown in untreated soil was 67% after 70 days. By contras~ this pesticide was undetectable after 28 days in the presence of the inoculant P . versicolor. This increased to 42 days where a mixture of the two fungi were used. Generally the mixture of fungi used in this study were not as effective in bioremediation of these pesticides as a single species. Field capacity soil appeared to be the best condition for P. versicolor to degrade dieldrin and trifluralin added at 10 ppm. However, for simazine this occurred in the driest water potential (-0.28 MPa) used.
Open Access
Carbon dioxide mediates the response to temperature and water activity levels in Aspergillus flavus during infection of maize kernels
(MDPI, 2017-12-22) Gilbert, Matthew K.; Medina-Vayá, Ángel; Mack, Brian M.; Lebar, Matthew D.; Rodriguez, Alicia; Bhatnagar, Deepak; Magan, Naresh; Obrian, Gregory; Payne, Gary
Aspergillus flavus is a saprophytic fungus that may colonize several important crops, including cotton, maize, peanuts and tree nuts. Concomitant with A. flavus colonization is its potential to secrete mycotoxins, of which the most prominent is aflatoxin. Temperature, water activity (aw) and carbon dioxide (CO2) are three environmental factors shown to influence the fungus-plant interaction, which are predicted to undergo significant changes in the next century. In this study, we used RNA sequencing to better understand the transcriptomic response of the fungus to aw, temperature, and elevated CO2 levels. We demonstrate that aflatoxin (AFB1) production on maize grain was altered by water availability, temperature and CO2. RNA-Sequencing data indicated that several genes, and in particular those involved in the biosynthesis of secondary metabolites, exhibit different responses to water availability or temperature stress depending on the atmospheric CO2 content. Other gene categories affected by CO2 levels alone (350 ppm vs. 1000 ppm at 30 °C/0.99 aw), included amino acid metabolism and folate biosynthesis. Finally, we identified two gene networks significantly influenced by changes in CO2 levels that contain several genes related to cellular replication and transcription. These results demonstrate that changes in atmospheric CO2 under climate change scenarios greatly influences the response of A. flavus to water and temperature when colonizing maize grain.
Open Access
Carbon dioxide production as an indicator of Aspergillus flavus colonisation and aflatoxins/cyclopiazonic acid contamination in shelled peanuts stored under different interacting abiotic factors
(Elsevier, 2019-10-24) Garcia Cela, Esther; Gari Sanchez, F. J.; Sulyok, Michael; Verheecke-Vaessen, Carol; Medina, Angel; Kruska, Rudolf; Magan, Naresh
Aspergillus flavus is the main xerophylic species colonising stored peanuts resulting in contamination with aflatoxins (AFs) and cyclopiazonic acid (CPA). This study evaluated the relationship between storage of shelled peanuts under interacting abiotic conditions on (a) temporal respiration (R) and cumulative CO2 production, (b) dry matter losses (DMLs) and (c) aflatoxin B1 (AFB1) and CPA accumulation. Both naturally contaminated peanuts and those inoculated with A. flavus were stored for 7-days under different water activities (aw; 0.77–0.95) and temperatures (20–35°C). There was an increase in the temporal CO2 production rates in wetter and warmer conditions, with the highest respiration at 0.95 aw + A. flavus inoculum at 30°C (2474 mg CO2kg−1h−1). The DMLs were modelled to produce contour maps of the environmental conditions resulting in maximum/minimum losses. Maximum mycotoxin contamination was always at 0.95 aw although optimal temperatures were 25-30°C for AFs and 30-35°C for CPA. These results showed a correlation between CO2 production and mycotoxin accumulation. They also provide valuable information for the creation of a database focused on the development of a post-harvest decision support system to determine the relative risks of contamination with these mycotoxins in stored shelled peanuts.
Open Access
Cladosporium species: the predominant species present on raspberries from the U.K. and Spain and their ability to cause skin and stigmata infections
(MDPI, 2023-01-17) Farwell, Lauren Helen; Deakin, Greg; Harris, Adrian Lee; Fagg, Georgina; Passey, Thomas; Verheecke-Vaessen, Carol; Magan, Naresh; Xu, Xiangming
Raspberry (Rosales: Rosaceae) production in the U.K. has moved rapidly in the last 10 years to under polythene, combined with a reduced availability of broad-spectrum fungicides. Hence, the incidence of previously less prevalent diseases, such as Cladosporium (Capnodiales: Cladosporiaceae), has largely increased. This study aimed to identify the predominant Cladosporium species on raspberry and to understand the nature of its infection on raspberry fruit. Raspberries were collected from farms across the U.K. and Spain and incubated; fungal isolates were then isolated from typical Cladosporium lesions and identified to the species level based on the sequences of the trans elongation factor α and actin genes. Cladosporium cladosporioides (Fres) de Vries was confirmed as the predominant species responsible for infecting raspberry fruit close to harvest on fruit from the U.K. and Spain, being present on 41.5% of U.K. fruit and 84.6% of Spanish fruit. Raspberries were subsequently inoculated at different developmental stages with C. cladosporioides isolates to determine the susceptibility to Cladosporium skin lesions and stigmata infections in relation to the developmental stage. Only the ripening and ripe raspberries were susceptible to Cladosporium, resulting in skin lesions. Cladosporium can colonise the stigmata of raspberries earlier in fruit development and future research is required to determine if such stigmata infections could cause subsequent skin lesion infections. This study has provided the necessary epidemiological information to develop effective management measures against the Cladosporium species.
Open Access
Climate change, food security and mycotoxins: do we know enough?
(Elsevier, 2017-05-18) Medina-Vayá, Ángel; Akbar, Asya; Baazeem, Alaa; Rodriguez, Alicia; Magan, Naresh
Climate change (CC) scenarios are predicted to have significant effects on the security of staple commodities. A key component of this impact is the infection of such crops by mycotoxigenic moulds and contamination with mycotoxins. The impacts of CC on mycotoxigenic fungi requires examination of the impacts of the three-way interactions between elevated CO2 (350–400 vs 650–1200 ppm), temperature increases (+2–5 °C) and drought stress on growth/mycotoxin production by key spoilage fungi in cereals and nuts. This review examines the available evidence on the impacts of interacting CC factors on growth and mycotoxin production by key mycotoxigenic fungi including Alternaria, Aspergillus, Fusarium and Penicillium species. Aspergillus flavus responsible for producing aflatoxin B1 (AFB1) is a class 1A carcinogen and its growth appears to be unaffected by CC factors. However, there is a significant stimulation of AFB1 production both in vitro and in vivo in maize. In contrast, studies on Aspergillus section Circumdati and Nigri species responsible for ochratoxin A contamination of a range of commodities and F. verticillioides and fumonisins suggest that some species are more resilient than others, especially in terms of mycotoxin production. Acclimatisation of mycotoxigenic fungal pathogens to CC factors may result in increased disease and perhaps mycotoxin contamination of staple cereals. Predictive modelling approaches to help identify regions where maximum impact may occur in terms of infection by mycotoxigenic fungi and toxin contamination of staple crops is hindered by the lack of reliable inputs on effects of the interacting CC factors. The present available knowledge is discussed in the context of the resilience of staple food chains and the impact that interacting CC factors may have on the availability of food in the future.
Open Access
Comparative growth inhibition of bread spoilage fungi by different preservative concentrations using a rapid turbidimetric assay system
(Frontiers, 2021-06-08) Valle Garcia, Marcelo; Garcia Cela, Esther; Magan, Naresh; Venturini Copetti, Marina; Medina, Angel
Bread and intermediate moisture bakery products are mainly spoiled by yeasts and filamentous fungi. The inoculum load and preservation system used determines their shelf life. To extend the shelf life of such commodities, the use of chemical preservatives is the most common way to try and control the initiation of mold spoilage of bread. This study has utilized a rapid turbidimetric assay system (Bioscreen C) to examine the temporal efficacy of calcium propionate (CP) and potassium sorbate (PS) for controlling the growth of important bread spoilage fungi. The objectives were to compare the temporal growth of strains of three important spoilage fungi Hyphopichia burtonii (HB17), Paecilomyces variotii (PV11), and Penicillium roqueforti (PR06) isolated from visibly molded bread to (a) different concentrations of CP and PS (0–128 mM), (b) temperatures (25°C, 30°C), (c) water activity (aw; 0.95, 0.97), and (d) pH (5.0, 5.5). All three abiotic factors, pH, aw, and temperature, and preservative concentrations influenced the relative growth of the species examined. In general, PS was more effective than CP in inhibiting the growth of the strains of these three species. In addition, the Time to Detection (TTD) for the efficacy of the preservatives under the interacting abiotic factors was compared. The strain of Paecilomyces variotii (PV10) was the most tolerant to the preservatives, with the shortest TTD values for both preservatives. P. roqueforti was the most sensitive with the longest TTD values under all conditions examined. These results are discussed in the context of the evolution of resistance to food-grade preservatives by such spoilage fungi in bakery products.
Open Access
Comparison of different bead-beating RNA extraction strategies: An optimized method for filamentous fungi
(Elsevier Science B.V., Amsterdam., 2012-03-01T00:00:00Z) Leite, Goncalo M.; Magan, Naresh; Medina-Vayá, Ángel
Molecular studies, especially in relation to the activity of secondary metabolite gene clusters, require the ability to extract good quality RNA from fungal biomass. This is often hindered by the cell wall structure and endogenous RNase activity in filamentous fungi. There is thus a need for rapid methods for the extraction of good quality RNA for use in microarrays and for quantitative PCR assays. The objective of this study was to examine the use of different systems for the high throughput method to extract intact RNA from filamentous fungi. Two bead beating systems with different motion patterns and speed capacities were tested in the development of the extraction protocol. They were evaluated based on the total RNA yield and overall RNA quality. The high speed bead beating with glass beads associated with an automated purification method gave more than three times higher total RNA yields with less than a quarter of the amount of mycelium required. Furthermore the integrity and overall quality was conserved, with RNA Quality Indicator (RQI) numbers consistently >7.5. This method also reduced cross contamination risks and kept RNA handling to a minimum while still being capable of multiple sample processing, reducing the time required to obtain RNA from filamentous fungi.