Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/1999
Publication Date: N/A
Interpretive Summary: Until recently, only three very closely related species of fungi were known to produce aflatoxin, the most potent naturally formed carcinogen. Two other species, Aspergillus tamarii and Aspergillus ochraceoroseus, have now been shown to produce aflatoxin. A. ochraceoroseus also produces a related toxin, sterigmatocystin. In this study, we made observations on the characteristics of the fungi to be sure they had been correctly identified, studied conditions under which these two species made the toxins, and checked to see if the genes for aflatoxin and sterigmatocystin production were similar to known genes for aflatoxin and sterigmatocystin. The toxigenic isolate of A. tamarii had some unusual physical features, but produced aflatoxin under conditions similar to that of known species and had very similar aflatoxin biosynthesis genes to those of known species. The A. ochraceoroseus isolate is unique in that it does not appear to be closely related to any of the known aflatoxin or sterigmatocystin producing fungi, produces toxins under somewhat different condition than recognized toxin-forming species, and the genes are also somewhat different from those of known species. These data suggest that the A. tamarii isolate may have acquired its aflatoxin genes through some kind of transfer from known species. The unique nature of aflatoxin/sterigmatocyst production by A. ochraceoroseus will give researchers new tools in understanding the nature of the production of these two toxins.
Technical Abstract: Until recently, only three species (Aspergillus flavus, A. parasiticus and A. nomius) have been widely recognized as producers of aflatoxin. In this study, we examine aflatoxin production by two other species, A. tamarii and A. ochraceoroseus, the latter of which also produces sterigmatocystin. Toxin-producing strains of A. tamarii and A. ochraceoroseus were examined morphologically, and toxin production was assayed on different media at different pH levels using thin layer chromatography and a densitometer. Genomic DNA of these two species was probed with known aflatoxin and sterigmatocystin biosynthesis genes from A. flavus/parasiticus and A. nidulans. Under the high stringency conditions, A. tamarii DNA hybridized to all four of the A. flavus/parasiticus gene probes, indicating strong similarities in the biosynthetic pathway genes of this species and those of A. flavus and A. parasiticus. The A. ochraceoroseus DNA hybridized weakly to the A. flavus/parasiticus verB gene probe, and to two of the three A. nidulans probes. These data indicate that, at the DNA level, the aflatoxin and sterigmatocystin biosynthetic pathway genes for A. ochraceoroseus are somewhat different from known pathway genes.