Safety of the fungal workhorses of industrial biotechnology: update on the mycotoxin and secondary metabolite potential of Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei

Abstract

This review presents an update on the current knowledge of the secondary metabolite potential of the major fungal species used in industrial biotechnology, i.e., Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei. These species have a long history of safe use for enzyme production. Like most microorganisms that exist in a challenging environment in nature, these fungi can produce a large variety and number of secondary metabolites. Many of these compounds present several properties that make them attractive for different industrial and medical applications. A description of all known secondary metabolites produced by these species is presented here. Mycotoxins are a very limited group of secondary metabolites that can be produced by fungi and that pose health hazards in humans and other vertebrates when ingested in small amounts. Some mycotoxins are species-specific. Here, we present scientific basis for (1) the definition of mycotoxins including an update on their toxicity and (2) the clarity on misclassification of species and their mycotoxin potential reported in literature, e.g., A. oryzae has been wrongly reported as an aflatoxin producer, due to misclassification of Aspergillus flavus strains. It is therefore of paramount importance to accurately describe the mycotoxins that can potentially be produced by a fungal species that is to be used as a production organism and to ensure that production strains are not capable of producing mycotoxins during enzyme production. This review is intended as a reference paper for authorities, companies, and researchers dealing with secondary metabolite assessment, risk evaluation for food or feed enzyme production, or considerations on the use of these species as production hosts.

Keywords: Industrial enzymes; Mycotoxins; Safety; Secondary metabolites.

Fig. 1

Macroscopic characteristics of 7-day old fungal species growing on solid medium (CYA). a Aspergillus niger; b A. oryzae; c A. flavus; d Trichoderma reesei (Photo: Birgitte Andersen)

Fig. 2

Phylogram based on whole genome sequences of available Aspergillus species within the Nigri and Flavi clades. The phylogram was made using kSNP (version 3.1; Gardner et al. 2015) which computes a core SNP matrix from all the genomes and then executed FastTree (Price et al. 2009) with the maximum likelihood option to compute the tree. The tree was then midpoint-rooted and rendered as a Phylogram using Dendroscope (Huson and Scornavacca 2012)