Location: Pest Management and Biocontrol ResearchTitle: Molecular analysis of S morphology aflatoxin producers from the United States reveals previously unknown diversity and two new taxa
|SINGH, PUMMI - University Of Arizona|
|ORBACH, MARC - University Of Arizona|
Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2020
Publication Date: 6/11/2020
Citation: Singh, P., Callicott, K.A., Orbach, M.J., Cotty, P.J. 2020. Molecular analysis of S morphology aflatoxin producers from the United States reveals previously unknown diversity and two new taxa. Frontiers in Microbiology. 11. https://doi.org/10.3389/fmicb.2020.01236.
Interpretive Summary: Aflatoxins are carcinogenic metabolites produced by fungi within Aspergillus section Flavi. Certain isolates with section Flavi have the small sclerotia or S morphology (< 400 µm) and contaminate crops with high concentrations of aflatoxins. Aflatoxin contamination of food and feed crops in both United States (US) and Africa has been attributed to S morphology fungi; however, knowledge of genetic diversity of these highly aflatoxigenic fungi in the US remains limited. The current study utilized molecular, phylogenetic and aflatoxin analyses to identify communities of S morphology fungi resident in regions of the US where crops are susceptible to aflatoxin contamination. Individual and concatenated phylogenies constructed using calmodulin (1.9 kb) and nitrate reductase (2.1 kb) genes along with deletions in norB-cypA genes of aflatoxin biosynthesis cluster resolved 494 S morphology fungi from the US into four species, including two previously undescribed species: A. flavus S morphotype (89.7%); 2) A. agricola sp. nov. (2.4%); 3) A. texensis (2.2%), and 4) A. toxicus sp. nov. (5.7%). Isolates of each species contaminated maize with high concentrations of aflatoxins at 25°C, 30°C and 35°C while A. flavus S morphotype produced unacceptable concentrations even at 40°C. Genetic diversity within A. flavus S morphotype was further dissected using 17 simple sequence repeat markers, which have successfully been used to study population structure of the L morphotype of A. flavus. Two hundred and two haplotypes were detected from 443 A. flavus S isolates with 3 to 20 alleles per locus indicating occurrence of multiple genotypes within A. flavus S morphotype. Identification and characterization of distinct communities and genotypes of aflatoxin-producing fungi in the US may influence aflatoxin management.
Technical Abstract: Aflatoxins are hepatocarcinogens produced by species within Aspergillus section Flavi that contaminate crops in warm regions. Several phylogenetically distinct fungi within section Flavi with S morphology (average sclerotial size < 400 µm) consistently produce high concentrations of aflatoxins in crops and, therefore, are a concern for the profitability of agriculture and the health of humans and domestic animals. S morphology fungi have been implicated as potentially important etiologic agents in the United States (US), however, little is known about their genetic diversity. The current study characterized S morphology fungi (n = 494) collected between 2002 and 2017 from soil and maize samples from regions in the US where aflatoxin contamination is a perennial problem. Phylogenetic analyses based on partial gene sequences of the calmodulin (1.9 kb) and nitrate reductase (2.1 kb) genes resolved S morphology isolates from the US into four distinct clades: 1) Aspergillus flavus S morphotype (89.7%); 2) A. agricola sp. nov. (2.4%); 3) A. texensis (2.2%), and 4) A. toxicus sp. nov. (5.7%). While all four S morphology species produced high concentrations of aflatoxins in maize at 25°C, 30°C and 35°C, the A. flavus S morphotype produced unacceptable aflatoxin concentrations even at 40°C. DNA fingerprinting of the A. flavus S isolates using 17 simple sequence repeat markers revealed high genetic diversity with 202 haplotypes from 443 isolates and 3 to 20 alleles per locus. Knowledge of the occurrence of distinct species and haplotypes of S morphology fungi that are highly aflatoxigenic under a range of environmental conditions may provide insights into the etiology, epidemiology, and management of aflatoxin contamination in North America.