Aspergillus flavus La3279, a component strain of the Aflasafe biocontrol product, contains a partial aflatoxin biosynthesis gene cluster followed by a genomic region highly variable among A. flavus isolates

Authors: Chang, Perng Kuang

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2022
Publication Date: 2/4/2022
Citation: Chang, P. 2022. Aspergillus flavus La3279, a component strain of the Aflasafe biocontrol product, contains a partial aflatoxin biosynthesis gene cluster followed by a genomic region highly variable among A. flavus isolates. International Journal of Food Microbiology. 366:109559. https://doi.org/10.1016/j.ijfoodmicro.2022.109559.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2022.109559

Interpretive Summary: Aspergillus flavus is a major producing mold of the carcinogenic aflatoxins. Physical and biological factors significantly affect pre- and post-harvest aflatoxin production on crops. Several biological methodologies have been explored to control aflatoxin contamination. Among them, the development of using multiple non-aflatoxigenic A. flavus strains to outcompete aflatoxigenic A. flavus in fields has become a major approach because of its effectiveness. In this study, the phylogenetic relationship among four component A. flavus strains of the biocontrol product, Aflasafe, was determined, and their genetic features were characterized. The obtained information will help future selection of suitable biocontrol strains and refining of biocontrol strategies to achieve the goal of reducing aflatoxin contamination of agricultural commodities.

Technical Abstract: Aspergillus flavus communities in agricultural fields consist of isolates with varying abilities to produce aflatoxins, which are highly toxic and carcinogenic to humans and animals. Biological control using multiple non-aflatoxigenic strains for formulation to outcompete aflatoxigenic A. flavus has become a mainstream strategy. Aflasafe composed of four strains, Ka16127, La3279, La3304 and Og0222, is such a biocontrol product first developed in Nigeria and now widely used on maize and groundnut. In this study, phylogenetic analyses based on genome-wide single nucleotide polymorphisms showed that Ka16127 and La3304 were closer to each other than to La3279, and the three were distant to Og0222. Detailed molecular characterization of La3279 indicated that its genome, contradictory to the published report, lacked approximately half of the aflatoxin gene cluster as well as the entire cyclopiazonic acid gene cluster. La3279 was a member of the previously known “pattern E” group, which includes A. flavus and Aspergillus oryzae isolates that have the aforementioned deletion followed by a 3.8-kb “E block” sequence insertion. In comparison to the E block, corresponding regions in typical aflatoxigenic S-morpho/genotype isolates and Ka16127 and La3304 as well were found missing 1.1 kb of the 5’ portion whereas L-morpho/genotype isolates contained a complete non-homologous region characterized by two and a half copies of A. flavus telomeric repeat sequence at one end. Regions corresponding to the E block were highly variable and were useful for classifying A. flavus isolates into groups that mostly contained both mating types. The presence of both mating-type genes in genetically closely related A. flavus suggests a previously active sexual cycle. It could facilitate the development of a refined biocontrol strategy such as deploying biocontrol strains with the same mating-type that is predominate in a field A. flavus population.