Genetic diversity of environmental Aspergillus flavus strains in the state of São Paulo, Brazil by random amplified polymorphic DNA

Abstract

Aspergillus flavus is a very important toxigenic fungus that produces aflatoxins, a group of extremely toxic substances to man and animals. Toxigenic fungi can grow in feed cropsAflatoxins constitute a group of low molecular weight compounds known to be extremely toxic to animals and man (Bennett & Klich 2003). They are secondary metabolites produced mainly by Aspergillus flavus and A. parasiticus, which are ubiquitous and cosmopolitan fungi able to grow on a wide variety of substrates. However, not all members of each species are toxigenic (Thapar 1988) and, even within potentially toxigenic strains, growth is not necessarily accompanied by toxin production, which depends on favorable environmental conditions such as temperature and humidity (Correa 2000). The economic losses due to fungal contamination and the high costs of control measures are enormous (Bennett & Keller 1997) and add up to billions of dollars worldwide (Pozzi 2000). For this reason, efforts on scientific research have been towards prevention rather than remedial action (Bennett & Keller 1997).The key action for preventing mycotoxins is to block the growth of toxigenic fungi (Fonseca et al. 1974, Bennett & Keller 1997. But this is not an easy task, since these microorganisms are widely spread through several ecosystems, covering vast geographical areas. Furthermore, they can be easily disseminated by wind and may contaminate food crops at different stages, including harvest, post-harvest, processing, transportation, and even at storage conditions in supermarkets.Several approaches can be adopted to prevent or minimize food contamination by aflatoxins, such as controlling potential toxigenic-fungi carriers (e.g., insects and rodents), reducing the storage period and controlling humidity and temperature (Correa 2000). The use of antifungal compounds and insecticides, in turn, has been increasingly criticized from the standpoint of environmental concerns, as well as being costly. The production of resistant-plant varieties, although not having yielded strong positive results, is considered to be a promising alternative (Trail et al. 1995) to prevent both A. flavus substrate colonization and aflatoxin production upon fungal proliferation. However, it is important to bear in mind that the host-parasite co-evolution frequently leads to an "arms race" (Ridley 2001), and it is thus unlikely that fungi remain stable with respect to their invasive or toxigenic potential, as they continuously adapt.The use of non-toxigenic strains for the biological control of toxigenic ones has already been suggested by Egel and collaborators (1994). The non-toxigenic varieties would be artificially disseminated in nature (Egel et al. 1994, Trail et al. 1995 to compete with the toxigenic strains, driving them out of their ecological niches (Trail et al. 1995). In experiments with plants artificially infected with non-toxigenic fugal strains, a reduction by up to 90% in the aflatoxin contamination was observed (Cotty 1989 apud Tran-Dinh et al. 1999). Yet promising, this ...

Molecular characterization of Aspergillus flavus and aflatoxin contamination of wheat grains from Saudi Arabia

“…Similar results have been described in other studies with Aspergillus spp, showing no correlation between DNA band profiles and production or non-production of AF (Lourenço et al, 2007).…”

“…RAPD was used for fourteen isolates of A. flavus from two geographically distinct sites in Brazil. Isolates were distributed in a non-random array, but one cannot assume that this is a fully discriminatory result, and thus, RAPD usefulness is debatable (Lourenço et al, 2007). Twenty-one isolates of Rhizoctonia solani were characterized by RAPD-PCR.…”

“…RAPD markers have detected genetic variability between the isolates of A. flavus and related species (Batista et al, 2008;Reddy et al, 2009;Irshad and Nawab, 2012). RAPD markers have been used to discriminate between aflatoxigenic from non-aflatoxigenic isolates of A. flavus (Lourenço et al, 2007;Gashgari et al, 2010). The inter-simple sequence repeat (ISSR) markers are highly polymorphic and are useful in studies on genetic diversity, phylogeny, gene tagging, genome mapping, and evolutionary biology (Reddy et al, 2002).…”

Molecular characterization of aflatoxigenic and non-aflatoxigenic Aspergillus flavus isolates collected from corn grains

“…The RAPD technique has been used to detect genetic variability between isolates of A. flavus and related species (Batista et al, 2008;Gehlot et al, 2011;Irshad and Nawab, 2012) and to discriminate between aflatoxigenic and non-aflatoxigenic isolates of A. flavus (Lourenço et al, 2007;Gashgari et al, 2010;Sepahvand et al, 2011). The ISSR technique has been employed to investigate the diversity and population structure of A. flavus (Tran-Dinh and Carter, 2000;Batista et al, 2008;Tran-Dinh et al, 2009;Hadrich et al, 2010;Wang et al, 2012) and to determine the similarities and dissimilarities between aflatoxigenic and non-aflatoxigenic isolates of this species (Tran-Dinh et al, 2009;Hatti et al, 2010).…”

Identificação molecular de isolados de fungos de interesse médico por meio de marcadores RAPD

“…2010 Identificação molecular de isolados de fungos de interesse médico por meio ... Sendo assim, a análise molecular é uma ferramenta importante no estabelecimento de um sistema complementar de identificação de fungos. Estudos recentes vêm aplicando técnicas moleculares como a análise do polimorfismo do DNA amplificado ao acaso (RAPD) (WILLIAMS ., 1990) o qual tem demonstrado ser um método rápido na identificação de espécies, tais como: A. fumigatus, Aspergillus terreus, Fusarium oxysporum, Fusarium sporotrichioides e Penicillium expansum (LEENDERS et al, 1996;HUE, 1999;RATH, 1999;SYMOENS, 2000;WILSON, 2004;LOURENÇO, 2007).…”