|CARBONE, IGNAZIO - North Carolina State University
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 4/25/2011
Publication Date: 9/9/2011
Citation: Moore, G.G., Beltz, S.B., Carbone, I., Ehrlich, K., Horn, B.W. 2011. The population dynamics of aflatoxigenic aspergilli. In: Guevara-Gonzalez, R.G., editor. Aflatoxins - Biochemistry and Molecular Biology. Rijeka, Croatia: Intech Open Access publishers. p. 347-366.
Technical Abstract: In the early eighteenth century, P.A. Micheli characterized the genus Aspergillus as an asexually reproducing species. Nearly a century later the first teleomorph was discovered and identified. Though other teleomorphs have been identified since Eurotium herbariorum (anamorph = A. glaucus), the genus Aspergillus is still considered to be predominately asexual. This belief was the foundation for stability of non-aflatoxigenic (AF-) biocontrol strains that are used to competitively exclude indigenous toxigenic Aspergilli in fields. The two U.S. Environmental Protection Agency-approved biocontrol strains are A. flavus isolates that are unable to synthesize aflatoxins due to either mutations in aflatoxin-synthesis pathway genes, or loss of those genes altogether. In 1998, Geiser et al. reported a cryptic sexual state in aflatoxigenic (AF+) A. flavus that suggests a history of recombination. If recombination is a frequent occurrence then it could affect the stability of the current biocontrol strains in the treated fields. Recently, a small contingent of the Aspergillus research community has emerged to explore population structure in AF+ Aspergilli. Evidence of genetic exchange and recombination is being sought by investigating populations of sympatric species within fields where AF+ fungi are sampled. Using population genetic methods that include linkage disequilibrium, ancestral recombination graphs, and allele coalescence within populations, inference of recombination has been achieved for two of the more common agents of aflatoxin contamination in agricultural commodities, A. flavus and A. parasiticus. Evidence of recombination in these fungi shows the necessity of population genetic studies for understanding the mechanisms that maintain functional and genetic diversity, and also in selection of improved biocontrol agents to better prevent aflatoxin contamination. In 2008, the MAT locus was characterized for A. flavus, A. parasiticus, and A. nomius which led to successful mating and teleomorph discoveries (Petromyces flavus, P. parasiticus and P. nomius) in 2009/2010. The discovery of a sexual state in AF+ species only intensifies the need for more stringent biocontrol strain selection strategies. Current research is investigating global Aspergillus populations for evidence of recombination, attempting to correlate distribution of mating-type genes and recombination with aflatoxin chemotype diversity, and looking at evidence of gene flow among populations and species. Future projects will endeavor to test the longevity and stability of biocontrol strains, through time-course studies with fluorescent (GFP)-labeled biocontrol strain dispersal in fields, and through mating tests between AF+ and AF- (biocontrol) strains.