Location: Pest Management and Biocontrol ResearchTitle: Phenotypic differentiation of two morphologically similar aflatoxin producers from West Africa
|SINGH, PUMMI - University Of Arizona|
|ORBACH, MARK - University Of Arizona|
Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2020
Publication Date: 10/13/2020
Citation: Singh, P., Callicott, K.A., Orbach, M., Cotty, P.J., Mehl, H.L. 2020. Phenotypic differentiation of two morphologically similar aflatoxin producers from West Africa. Toxins. 12(10). Article 656. https://doi.org/10.3390/toxins12100656.
Interpretive Summary: Aflatoxins are hepatocarcinogenic metabolites produced by fungi within Aspergillus section Flavi. Aspergilli with small sclerotia or S morphology (<400 µm) contaminate crops with high concentrations of aflatoxins and have been implicated as causal agents of contamination episodes in the US and Africa. Aspergillus aflatoxiformans and A. minisclerotigenes can infect and contaminate maize, groundnuts and chilies with dangerous concentrations of aflatoxins. Accurate identification of these species is difficult because isolates of both species demonstrate similar phenotypes in terms of morphological and physiological characteristics. However, co-occurrence of these two species in West Africa and their ability to infect similar host crops can result in mixed infections complicating the etiology of crop contamination. The two species can be reliably differentiated using DNA markers, however, DNA-based techniques may have restricted availability or accessibility in West Africa where these species co-occur. The current study describes physiology of isolates of A. aflatoxiformans and A. minisclerotigenes in three liquid fermentation media, including chemically defined Adye and Mateles medium supplemented with urea or ammonium as sole nitrogen source and yeast extract with sucrose (YES) medium. Based on the ability of A. minisclerotigenes to produce significantly higher concentrations of aflatoxins in the YES medium irrespective of pH conditions or sucrose concentrations, a rapid and convenient microbiological assay is proposed to reliably differentiate the two species. This assay can be useful for accurate identification of isolates of A. aflatoxiformans and A. minisclerotigenes towards understanding the etiology of crop contamination in West Africa and devising mitigation strategies.
Technical Abstract: Aflatoxins (AF) are hepatocarcinogenic metabolites produced by species within Aspergillus section Flavi. Aflatoxins contaminate cereals, groundnuts, tree nuts, and spices in warm regions of the world. Etiology of aflatoxin contamination may be complicated by mixed infections of multiple species with similar morphology and aflatoxin profiles. The current study investigates the physiology of A. aflatoxiformans and A. minisclerotigenes in liquid fermentation. These species co-exist in West Africa and have overlapping phenotypes. Both species contaminate maize with large concentrations of aflatoxins under various environmental conditions and therefore to attribute etiologies of specific events, reliable differentiation of these fungi is needed. During liquid fermentation experiments, a physiological distinction between these two species was discovered, which is sufficient to differentiate the species and may be useful when DNA technology is unavailable. The two species were compared in liquid fermentation in defined media containing either urea or ammonium as sole nitrogen sources, and a yeast-extract based medium with sucrose (YES). The species produced similar concentrations of AFB1 in media with urea or ammonium (p > 0.05), but AFB1 production was inhibited for A. aflatoxiformans in YES medium (p < 0.001). Although production of AFG1 by both species was similar in urea, A. minisclerotigenes produced higher concentrations of AFG1 in ammonium (p = 0.039). Similar to AFB1, AFG1 production by A. aflatoxiformans was inhibited in YES medium. A reliable and convenient assay for differentiating the two species was designed. This assay may be useful for identifying specific etiologic agents of aflatoxin contamination episodes in West Africa.