Variation in fumonisin and ochratoxin production associated with differences in biosynthetic gene content in Aspergillus niger and A. welwitschiae isolates from multiple crop and geographic origins

Authors: SUSCA, ANTONIA - National Research Council - Italy; MORELLI, MASSIMILIANO - National Research Council - Italy; HAIDUKOWSKI, MIRIAM - National Research Council - Italy; GALLO, ANTONIA - National Research Council - Italy; Proctor, Robert; LOGRIECO, ANTONIO - National Research Council - Italy; MORETTI, ANTONIO - National Research Council - Italy

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2016
Publication Date: 9/9/2016
Publication URL: https://handle.nal.usda.gov/10113/5695399
Citation: Susca, A., Proctor, R.H., Morelli, M., Haidukowski, M., Gallo, A., Logrieco, A.F., Moretti, A. 2016. Variation in fumonisin and ochratoxin production associated with differences in biosynthetic gene content in Aspergillus niger and A. welwitschiae isolates from multiple crop and geographic origins. Frontiers in Microbiology. doi: 10.3389/fmicb.2016.01412.

Interpretive Summary: The fungi Aspergillus niger and A. welwitschiae are used for industrial fermentation processes and for preparation of some foods and beverages. These fungi also occur on food crops as members of communities of microorganisms that exist on plants. Concerns about the safety of A. niger and A. welwitschiae arose after the discovery that some strains of both species produce fumonisins and ochratoxins, two groups of toxins that pose health risks to humans and animals. The goal of the current study was to determine the frequency of fumonisin and ochratoxin-producing and nonproducing isolates in a collection of strains of A. niger and A. welwitschiae isolated from multiple crop and geographic origins. In addition, the strains were assessed for the presence and absence of genes responsible for biosynthesis of the two toxins. A majority of A. niger strains and a minority of A. welwitschiae strains produced fumonisins, but a minority of strains of both species produced ochratoxins. Few strains of either species produced both toxins. Not surprisingly, strains that produced a toxin had all the genes required for its biosynthesis. In addition, fumonisin-nonproducing strains of A. niger had all the fumonisin biosynthetic genes, but fumonisin-nonproducing strains of A. welwitschiae lacked two – eight fumonisin biosynthetic genes. For both species, strains that did not produce ochratoxin lacked ochratoxin biosynthetic genes. These results indicate that relatively simple DNA-based assays should be useful for predicting the potential of both species to produce ochratoxins and for A. welwitschiae to produce fumonisins, but not for A. niger to produce fumonisins. This study expands the understanding of toxin producing fungi. The results will be of use to academic, government, and private-sector organizations working to develop methods to reduce toxin contamination in crops.

Technical Abstract: The fungi Aspergillus niger and A. welwitschiae are morphologically indistinguishable species used for industrial fermentation and for food and beverage production. The fungi also occur widely on food crops. Concerns about their safety have arisen with the discovery that some isolates of both species produce fumonisins (FB) and ochratoxin A (OTA) mycotoxins. Here, we examined FB and OTA production as well as the presence of genes responsible for synthesis of the mycotoxins in a collection of 92 A. niger/A. welwitschiae isolates from multiple crop and geographic origins. The results indicate that i) isolates of both species differed in ability to produce the mycotoxins; ii) FB-nonproducing isolates of A. niger had an intact fumonisin biosynthetic gene (fum) cluster; iii) FB-nonproducing isolates of A. welwitschiae collectively exhibited 12 patterns of fum gene deletion; and iv) OTA-nonproducing isolates of both species lacked the ochratoxin A biosynthetic gene (ota) cluster. Analysis of genome sequence data revealed a single pattern of ota gene deletion in the two species. We propose that the simplest explanation for this is that ota cluster deletion occurred in a common ancestor of A. niger and A. welwitschiae, and subsequently both the intact and deleted cluster were retained as alternate alleles during divergence of the ancestor into descendent species. Finally, comparison of results from this and previous studies indicate that a majority of A. niger isolates and a minority of A. welwitschiae isolates can produce FBs, whereas a minority of isolates of both species produce OTA. The comparison also suggested that the relative abundance of each species and frequency of FB/OTA-producing isolates can vary with crop and/or geographic origin.