Browsing by Author "Rodriguez, Alicia"
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Item 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, NareshThis 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.Item 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, GaryAspergillus 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.Item 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, NareshClimate 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.Item Open Access Effect of climate change on Aspergillus flavus and aflatoxin B-1 production(Frontiers Media, 2014-07-22) Medina-Vayá, Ángel; Rodriguez, Alicia; Magan, NareshThis review considers the available information on the potential impact of key environmental factors and their interactions on the molecular ecology, growth and aflatoxin production by Aspergillus flavus in vitro and in maize grain. The recent studies which have been carried out to examine the impact of water activity × temperature on aflatoxin biosynthesis and phenotypic aflatoxin production are examined. These have shown that there is a direct relationship between the relative expression of key regulatory and structural genes under different environmental conditions which correlate directly with aflatoxin B1 production. A model has been developed to integrate the relative expression of 10 biosynthetic genes in the pathway, growth and aflatoxin B1 (AFB1) production which was validated under elevated temperature and water stress conditions. The effect of interacting conditions of aw × temperature × elevated CO2 (2 × and 3 × existing levels) are detailed for the first time. This suggests that while such interacting environmental conditions have little effect on growth they do have a significant impact on aflatoxin biosynthetic gene expression (structural aflD and regulatory aflR genes) and can significantly stimulate the production of AFB1. While the individual factors alone have an impact, it is the combined effect of these three abiotic factors which have an impact on mycotoxin production. This approach provides data which is necessary to help predict the real impacts of climate change on mycotoxigenic fungi.Item Open Access Evaluation of the risk of fungal spoilage when substituting sucrose with commercial purified Stevia glycosides in sweetened bakery products(Elsevier, 2016-04-27) Rodriguez, Alicia; Magan, Naresh; Medina-Vayá, ÁngelThe objectives of this study were to compare the effect of different Stevia-based sugar substitutes (S1–S3), sucrose alone and a mixture of sucrose + S1 on: (a) humectant properties, (b) relative colonisation rates of sponge cake slices at 0.90 aw by strains of Aspergillus flavus, Eurotium amstelodami, Fusarium graminearum and Penicillium verrucosum at 20 and 25 °C and (c) shelf-life periods in days prior to visible growth. Results showed that sucrose, S1 commercial sugar substitute and the mixture of sucrose + S1 in water solutions were able to reach water activity levels similar to those of glycerol and glucose mixtures. The S2 and S3 commercial sugar substitutes were unable to reduce aw levels significantly. At 25 °C, colonisation of sponge cake slices by E. amstelodami, A. flavus and P. verrucosum occurred in all the treatments. Growth of F. graminearum only occurred on sponge cake slices containing S2 and S3 Stevia-based products at both temperatures. The best control of growth (30 days) was achieved in cake slices modified with sucrose or S1 Stevia treatments inoculated with A. flavus and in the sucrose treatment for E. amstelodami at 20 °C. F. graminearum growth was completely inhibited when sucrose alone, S1 or sucrose + S1 treatments were used at both temperatures. This study suggests that, as part of a hurdle technology approach, replacing sucrose with low calorie sugar substitutes based on Stevia glycosides needs to be done with care. This is because different products may have variable humectant properties and bulking agents which may shorten the potential shelf-life of intermediate moisture bakery products.Item Open Access Impacts of climate change interacting abiotic factors on growth, aflD and aflR gene expression and aflatoxin B1 production by Aspergillus flavus strains in vitro and on pistachio nuts(MDPI, 2021-05-28) Baazeem, Alaa; Rodriguez, Alicia; Medina, Angel; Magan, NareshPistachio nuts are an important economic tree nut crop which is used directly or processed for many food-related activities. They can become colonized by mycotoxigenic spoilage fungi, especially Aspergillus flavus, mainly resulting in contamination with aflatoxins (AFs), especially aflatoxin B1 (AFB1). The prevailing climate in which these crops are grown changes as temperature and atmospheric CO2 levels increase, and episodes of extreme wet/dry cycles occur due to human industrial activity. The objectives of this study were to evaluate the effect of interacting Climate Change (CC)-related abiotic factors of temperature (35 vs. 37 °C), CO2 (400 vs. 1000 ppm), and water stress (0.98–0.93 water activity, aw) on (a) growth (b) aflD and aflR biosynthetic gene expression and (c) AFB1 production by two strains A. flavus (AB3, AB10) in vitro on milled pistachio-based media and when colonizing layers of shelled raw pistachio nuts. The A. flavus strains were resilient in terms of growth on pistachio-based media and the colonisation of pistachio nuts with no significant difference when exposed to the interacting three-way climate-related abiotic factors. However, in vitro studies showed that AFB1 production was significantly stimulated (p < 0.05), especially when exposed to 1000 ppm CO2 at 0.98–0.95 aw and 35 °C, and sometimes in the 37 °C treatment group at 0.98 aw. The relative expression of the structural aflD gene involved in AFB1 biosynthesis was decreased or only slightly increased, relative to the control conditions at elevated CO, regardless of the aw level examined. For the regulatory aflR gene expression, there was a significant (p < 0.05) increase in 1000 ppm CO2 and 37 °C for both strains, especially at 0.95 aw. The in situ colonization of pistachio nuts resulted in a significant (p < 0.05) stimulation of AFB1 production at 35 °C and 1000 ppm CO2 for both strains, especially at 0.98 aw. At 37 °C, AFB1 production was either decreased, in strain AB3, or remained similar, as in strain AB10, when exposed to 1000 ppm CO2. This suggests that CC factors may have a differential effect, depending on the interacting conditions of temperature, exposure to CO2 and the level of water stress on AFB1 production.Item Open Access The influence of ecophysiological factors on growth, aflR gene expression and aflatoxin B1 production by a type strain of Aspergillus flavus(Elsevier, 2017-05-18) Bernaldez, Victoria; Cordoba, Juan J.; Magan, Naresh; Peromingo, Belén; Rodriguez, AliciaMaize is prone to infection by Aspergillus flavus, which can contaminate the product with aflatoxins. The objective of this study was to examine the impact that interactions between water activity (aw) and temperature may have on growth, the expression of a biosynthetic regulatory gene (aflR) and aflatoxin B1 (AFB1) production by a strain of A. flavus on a maize-based medium. Results showed that there were some differences between lag phases and growth rates of A. flavus. The optimum growth rate for A. flavus was at 30 °C and 0.99 aw. No growth occurred at 0.90 aw and 20 °C. Both temperature and aw had an influence on the relative aflR gene expression and AFB1 production by A. flavus; however, the results for AFB1 production were not consistent with the effects on gene expression or growth. These findings provide data that are useful to better understand the conditions which represent higher risks from AFB1 production. However, the aflR expression was not a good indicator of AFB1 production alone. Thus, further molecular studies of other AF-related genes should be done. These results are discussed in the context of harvesting and storage of maize and the prevailing environmental conditions to minimise AFB1 contamination.Item Open Access Insights into existing and future fungal and mycotoxin contamination of cured meats(Elsevier, 2019-07-31) Perrone, Giancarlo; Rodriguez, Alicia; Magistà, Donato; Magan, NareshCured meats are widely consumed in various regions of the world and, as for other foods, consumers are increasingly aware of the need for better quality and safety. Various fungal communities can colonise meat products during their curing with beneficial or detrimental effects depending on the dominant species. Some contribute to flavour, anti-oxidative and protective effects, while others cause spoilage, including undesirable off-flavours/odours and mycotoxin contamination. Recently, increasing research on fungal ecophysiology and mycotoxin occurrence, especially of ochratoxin A (OTA) and aflatoxins, has been shown in these products. This review addresses the existing and new knowledge which is available to provide insights into the reasons why certain fungi colonise cured meats including their ecology, the importance of critical control points and effective use of new monitoring methods for evaluating the risk of mycotoxin contamination of these products.Item Open Access Interactions between water activity and temperature on the Aspergillus flavus transcriptome and aflatoxin B1 production(Elsevier, 2017-05-26) Medina-Vayá, Ángel; Gilbert, Matthew K.; Mack, Brian M.; OBrian, Gregory R.; Rodriguez, Alicia; Bhatnagar, Deepak; Payne, Gary; Magan, NareshEffects of Aspergillus flavus colonization of maize kernels under different water activities (aw; 0.99 and 0.91) and temperatures (30, 37 °C) on (a) aflatoxin B1 (AFB1) production and (b) the transcriptome using RNAseq were examined. There was no significant difference (p = 0.05) in AFB1 production at 30 and 37 °C and 0.99 aw. However, there was a significant (p = 0.05) increase in AFB1 at 0.91 aw at 37 °C when compared with 30 °C/0.99 aw. Environmental stress effects using gene ontology enrichment analysis of the RNA-seq results for increasing temperature at 0.99 and 0.91 aw showed differential expression of 2224 and 481 genes, respectively. With decreasing water availability, 4307 were affected at 30 °C and 702 genes at 37 °C. Increasing temperature from 30 to 37 °C at both aw levels resulted in 12 biological processes being upregulated and 9 significantly downregulated. Decreasing aw at both temperatures resulted in 22 biological processes significantly upregulated and 25 downregulated. The interacting environmental factors influenced functioning of the secondary metabolite gene clusters for aflatoxins and cyclopiazonic acid (CPA). An elevated number of genes were co-regulated by both aw and temperature. An interaction effect for 4 of the 25 AFB1 genes, including regulatory and transcription activators occurred. For CPA, all 5 biosynthetic genes were affected by aw stress, regardless of temperature. The molecular regulation of A. flavus in maize is discussed.