Mycotoxins

Abstract

Mycotoxins are a class of natural fungal metabolites that are specifically toxic to mammals and are frequent contaminants of foods and feeds. In this article we describe mycotoxins from Ascomycota or sac fungi, the largest phylum of fungi, which includes penicillia, aspergilli, fusaria, alternaria, claviceps and other non‐Basidiomycota (‘higher fungi’ or mushroom‐producing) genera. We discuss the toxicity and biosynthesis of the most agriculturally important mycotoxins, namely, polyketide toxins (fumonisins, aflatoxins, ochratoxins, patulin and zearalenone), nonribosomal peptide toxins (ergot alkaloids and tremorgenic toxins) and trichothecenes produced via the terpene biosynthesis pathway. The Ascomycota produce mycotoxins in crops both before harvest and during storage. The genes required for biosynthesis are usually clustered. Transcriptional regulation of biosynthesis involves a pathway‐specific Cys 6 Zn 2 type protein as well as a secondary metabolite‐specific methyltransferase, LaeA. Both of these transcription factors are unique to fungi. Hypotheses about the evolution of mycotoxin biosynthesis in fungi are discussed. Key Concepts: Mycotoxins are produced by ascomycete (‘lower’) fungi in certain agriculturally important crops. The most common mycotoxins exert a variety of generally nonlethal toxic effects in animals. Biosynthesis of mycotoxins usually involves a co‐regulated, clustered set of genes on one chromosome. Co‐regulation involves transcription factors of the Cys 6 Zn 2 type and a putative methyltransferase, LaeA. Mycotoxins can be of several types: polyketides, nonribosomal peptides or terpene‐derived metabolites. Mycotoxin biosynthesis has evolved in fungi in the absence of agriculture and is not strictly associated with fungal virulence in contaminated crops.

Mapping the Fungal Battlefield: Using in situ Chemistry and Deletion Mutants to Monitor Interspecific Chemical Interactions Between Fungi

“…For example, the relative abundance of the mycotoxins verruculogen ( 6 ) (on average 99-fold) and fumitremorgin B ( 5 ) (on average 156-fold) increased in co-culture versus monoculture, as seen by the area under the curve (Supplementary Table S3). This was observed across three separate biological replicates in situ , suggesting that A. fischeri increased the abundance of its mycotoxin biosynthesis to better compete with X. cubensis (Reverberi et al, 2010; Ehrlich et al, 2011).…”

Wheldone: Characterization of a Unique Scaffold from the Coculture of Aspergillus fischeri and Xylaria flabelliformis

“…Aspergillus fischeri (strain NRRL 181) was chosen as the challenger due to its genetic tractability and the biosynthesis of metabolite weaponry in the form of mycotoxins. − Indeed, bioinformatic analysis of the genomes of both organisms predicted the presence of as many as 48 biosynthetic gene clusters for A. fischeri and 86 biosynthetic gene clusters for X. flabelliformis , yet only a relatively narrow range of secondary metabolites has been reported from either fungus. Our hypothesis was that the stress caused by the chemical warfare between these organisms would activate “silent” biosynthetic gene clusters and generate unprecedented chemical diversity. ,− …”

“…22 There were several known metabolites identified in the junction that were not observed in the monoculture, as reported recently. 23,25,26 However, there was one minor peak that did not match with any metabolites in an in-house database of over 525 fungal metabolites, 31 that could not be characterized via mass defect filtering, 32 and whose molecular formula and spectroscopic data did not correlate to any organic compounds in the literature. Thus this metabolite was targeted for isolation and characterization.…”