Aspergillus texensis: A novel aflatoxin producer with S morphology from the United States

Authors: SINGH, PUMMI - University Of Arizona; ORBACH, MARC - University Of Arizona; Cotty, Peter

Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2018
Publication Date: 12/3/2018
Citation: Singh, P., Orbach, M.J., Cotty, P.J. 2018. Aspergillus texensis: A novel aflatoxin producer with S morphology from the United States. Toxins. 10(12):1-15. https://doi.org/10.3390/toxins10120513.
DOI: https://doi.org/10.3390/toxins10120513

Interpretive Summary: Aflatoxins are carcinogenic metabolites that contaminate a wide range of crops, including maize, groundnuts, spices and tree nuts. Aflatoxin contamination of maize in the United States (US) results in severe economic losses to growers, and contamination of crops with aflatoxins remains a concern. Strategies for aflatoxin mitigation include understanding etiology of contamination, which requires identification and characterization of aflatoxin-producers. The current study describes a novel aflatoxin producing species, Aspergil/us texensis, recovered from soils cropped to maize and maize kernels from the US. The novel species was discovered during phylogenetic analysis of fungi with S morphology from Aspergillus section Flavi. Fungi with S morphology consistently produce high concentrations of aflatoxins on crops and can result in dangerous levels of contamination even when incidences are low. Aspergil/us texensis has an S morphology and produces sparse conidia but abundant small sclerotia (<400 µm) on multiple culture media and maize. Fungal isolates had optimal growth at 35° C and produced aflatoxins Band G, aspergillic acid and cyclopiazonic acid. Aspergillus texensis produced dangerous concentrations of total aflatoxins on maize. Phylogenetic analysis using beta-tubulin (0.9 kb), calmodulin (1.2 kb) and nitrate reductase (2.1 kb) clearly placed A texensis into a highly supported monophyletic clade. Aspergillus texensis is sister to A. minisc/erotigenes and the Lethal Aflatoxicosis Fungus. Occurrence of this novel aflatoxin producing species in the US may have implications on aflatoxin contamination of crops and management.

Technical Abstract: Aflatoxins are carcinogenic metabolites produced by fungi within Aspergil/us section Flavi that colonize a wide range of crops in warm regions. Molecular phylogenetic analysis of fungi with S morphology (average sclerotia size <400 µm) collected from across the United States resulted in the discovery of a novel aflatoxin-producing species, Aspergillus texensis. Aspergillus texensis was isolated from maize grown in Arkansas, Louisiana, and Texas, and from soils cropped to maize in Texas. Morphological studies showed that A. texensis produces sparse conidia and large quantities of sclerotia on various culture media and maize. Physiological studies revealed optimal growth on culture media at 35° C. All isolates of A texensis produced B and G aflatoxins, cyclopiazonic acid and aspergillic acid. Aspergil/us texensis and A. flavus S strain morphotype produced similar concentrations of total aflatoxins on maize (p > 0.05). Phylogenetic analyses of aflatoxin-producers based on partial gene sequences of the beta-tubulin (0.9 kb), calmodulin (1.2 kb), and nitrate reductase (2.1 kb) genes placed A. texensis in a highly supported monophyletic clade closely related to A. minisc/erotigenes and the Lethal Aflatoxicosis Fungus.