Secondary Metabolite Dereplication and Phylogenetic Analysis Identify Various Emerging Mycotoxins and Reveal the High Intra-Species Diversity in Aspergillus flavus

Abstract

Aspergillus flavus is one of the most important mycotoxigenic species from the genus Aspergillus , due to its ability to synthesize the potent hepatocarcinogen, aflatoxin B 1 . Moreover, this fungus is capable of producing several other toxic metabolites from the class of indole-tetramates, non-ribosomal peptides, and indole-diterpenoids. Populations of A. flavus are characterized by considerable diversity in terms of morphological, functional and genetic features. Although for many years A. flavus was considered an asexual fungus, researchers have shown evidence that at best these fungi can exhibit a predominantly asexual existence. We now know that A. flavus contains functional genes for mating, uncovering sexuality as potential contributor for its diversification. Based on our results, we reconfirm that A. flavus is a predominant producer of B-type aflatoxins. Moreover, this fungus can decisively produce AFM 1 and AFM 2 . We did not observe any clear relationship between mating-type genes and particular class of metabolites, probably other parameters such as sexual/asexual ratio should be investigated. A dynamic secondary metabolism was found also in strains intended to be used as biocontrol agents. In addition we succeeded to provide mass spectrometry fragmentation spectra for the most important classes of A. flavus metabolites, which will serve as identification cards for future studies. Both, metabolic and phylogenetic analysis proved a high intra-species diversity for A. flavus . These findings contribute to our understanding about the diversity of Aspergillus section Flavi species, raising the necessity for polyphasic approaches (morphological, metabolic, genetic, etc.) when dealing with this type of complex group of species.

Diversity and toxigenicity of fungi and description of Fusarium madaense sp. nov. from cereals, legumes and soils in north-central Nigeria

“…The extrolite patterns of the Aspergillus species, isolated and identified in this study, except A. tamarii which was not evaluated, are shown in Table 1. Members of the section Flavi produced metabolites (aflatoxins and their biosynthetic pathway precursors, asparason A, cyclopiazonic acid, desoxypaxillin, kojic acid, kotanin A, paspalin and paspalitrems) consistent with previous reports (Frisvad et al 2019, Uka et al 2019. However, some new findings are reported herein.…”

“…However, some new findings are reported herein. For example, desoxypaxillin, heptelidic acid, kotanin A and paspalitrems were previously reported in A. flavus (Uka et al 2019, Kovac et al 2020, but not in A. aflatoxiformans, A. austwickii and A. cerealis. Hence, we present the first report of desoxypaxillin, kotanin A (mean: 534 µg/kg) and paspalitrems in the three S-type sclerotium (minisclerotium) producing species and heptelidic acid (10.2 mg/kg) only in A. austwickii.…”

Fungal Diversity and Mycotoxins in Low Moisture Content Ready-To-Eat Foods in Nigeria

“…Four A. flavus strains were considered for metabolite profiling; three strains were aflatoxigenic while the DTO 481-G5 strain was non-aflatoxigenic but produced cyclopiazonic acid and kojic acid. The aflatoxigenic strains produced the B aflatoxins together with other known metabolites including 3-nitropropionic acid, aflatrem, aflavarins, asparason A cyclopiazonic acid, desoxypaxillin, kojic acid, kotanin A, paspalin and paspalitrems; Frisvad et al, 2019;Uka et al, 2019). We also found heptelidic acid in a culture of one aflatoxigenic A. flavus strain; this corroborates the findings of a previous study from our group wherein we reported this metabolite in both mycelia and culture media extracts of aflatoxigenic A. flavus (Kovač et al, 2020).…”

Comparative Toxigenicity and Associated Mutagenicity of Aspergillus fumigatus and Aspergillus flavus Group Isolates Collected from the Agricultural Environment

“…It must be stressed that AFM 1 , which is mainly considered as a liver-hydroxylated metabolite of AFB 1 , was detected in the (Flav + ) extract. This direct production of AFM 1 by A. flavus was also recently reported by Uka et al [16], but does not appear to have been commonly described. A significant direct mutagenicity was observed in TA98 for (Flav + ) and (Para + ) extracts as well as for pure AFB 1 .…”

“…Moreover, the absence of mutagenicity for (Flav -) and (Para -) extracts could indicate that additional metabolites are closely related to the AFB 1 synthesis pathway. Recently, Uka et al [16] highlighted the particularly high intra-species diversity of A. flavus and reported the large variety of secondary metabolites that can be produced. Using a metabolomic approach on 55 isolates of A. flavus, they identified more than 50 metabolites even if only half of the 55 strains were considered as aflatoxin producers.…”