|MEHL, HILLARY - University Of Arizona|
|COTTY, PETER - US Department Of Agriculture (USDA)|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2012
Publication Date: 3/1/2013
Citation: Mehl, H.L., Cotty, P.J. 2013. Nutrient environment influences competition among Aspergillus flavus genotypes. Applied and Environmental Microbiology. 79:1473-1480.
Interpretive Summary: Aflatoxins, toxic fungal metabolites produced by Aspergillus flavus and related fungi, frequently contaminate food and feed crops in warm production areas. An effective means of aflatoxin mitigation is through competitive displacement of aflatoxin-producing fungi with atoxigenic strains of A. flavus, but further work is needed to identify specific mechanisms dictating competitive interactions among these fungi. In the current study, we quantified the extent to which nutrient environments influence outcomes of competition between different isolates of A. flavus. Results demonstrate different nutrient environments dictate the competitive success of individual A. flavus. Thus, nutrients influence the structure of aflatoxin-producing fungal populations and, in so doing, incidences and severities of aflatoxin contamination. Selection of atoxigenic strains for biocontrol of aflatoxin contamination should take into consideration performance of isolates in the different nutrient environments, including plant hosts and soil matrices, they are likely to encounter in the field.
Technical Abstract: Structures of Aspergillus flavus populations, shaped by intraspecific competition, influence the incidences and severities of crop aflatoxin contamination. Competition for nutrients may be one factor modulating intraspecific interactions, but influences of specific types and concentrations of nutrients on competition among genotypes of A. flavus have not been quantified. Competition among A. flavus isolates on agar media was influenced by varying concentrations of carbon (sucrose or asparagine) and nitrogen (nitrate or asparagine). Incidences of co-cultivated isolates within conidia and agar-embedded mycelia were quantified by measurement of isolate-specific single nucleotide polymorphisms with quantitative pyrosequencing. Compositions and concentrations of nutrients influenced incidences of isolates in conidia resulting from co-cultivation, but sporulation by isolates grown individually did not predict competitive ability during reproduction. Success during sporulation did not reflect outcomes of competition during mycelial growth, and the extent to which isolate proportions in conidia differed from proportions in mycelia varied among isolates and media. Sucrose, nitrate, and asparagine all influenced competition but the magnitude of the influence varied among co-cultivated isolates. Differential responses of A. flavus isolates to nutrients suggest genotypes are adapted to different nutrient environments. The nutrient environment (i.e. the composition and concentration of nutrients within which the fungus grows) thus has the potential to influence A. flavus population structure and the epidemiology of aflatoxin contamination.