Racemic gossypol and its related derivatives gossypolone and apogossypolone demonstrated significant growth inhibition against a diverse collection of filamentous fungi that included Aspergillus flavus, Aspergillus parasiticus, Aspergillus alliaceus, Aspergillus fumigatus, Fusarium graminearum, Fusarium moniliforme, Penicillium chrysogenum, Penicillium corylophilum, and Stachybotrys atra. The compounds were tested in a Czapek agar medium at a concentration of 100 μg/mL. Racemic gossypol and apogossypolone inhibited growth by up to 95%, whereas gossypolone effected 100% growth inhibition in all fungal isolates tested except A. flavus. Growth inhibition was variable during the observed time period for all tested fungi capable of growth in these treatment conditions. Gossypolone demonstrated significant aflatoxin biosynthesis inhibition in A. flavus AF13 (B(1), 76% inhibition). Apogossypolone was the most potent aflatoxin inhibitor, showing greater than 90% inhibition against A. flavus and greater than 65% inhibition against A. parasiticus (B(1), 67%; G(1), 68%). Gossypol was an ineffectual inhibitor of aflatoxin biosynthesis in both A. flavus and A. parasiticus. Both gossypol and apogossypolone demonstrated significant inhibition of ochratoxin A production (47%; 91%, respectively) in cultures of A. alliaceus.

Production of carcinogenic aflatoxins has been reported from members of Aspergillus section Flavi, Aspergillus section Nidulantes and a newly proposed Aspergillus section Ochraceorosei that consists of Aspergillus ochraceoroseus and A. rambellii. Unlike members of section Flavi, A. ochraceoroseus and A. rambellii have been shown to accumulate both aflatoxin (AF) and the aflatoxin precursor sterigmatocystin (ST). Alhough morphologically distinct from A. nidulans, molecular characterization of A. ochraceoroseus AF/ST genes and physiological characteristics of AF/ST production indicated that A. ochraceoroseus is more closely related to A. nidulans than to A. flavus. Knowing that the A. nidulans ST gene cluster is organized differently from the A. flavus AF gene cluster, we determined the genetic organization of the AF/ST biosynthetic cluster in A. ochraceoroseus. Sequencing of overlapping lambda clones and genomic PCR fragments obtained by gene-walking techniques demonstrated that the A. ochraceoroseus AF/ST gene cluster is organized much like the A. nidulans ST gene cluster except that the region from aflN to aflW is located directly upstream of aflC and in reverse orientation such that aflW represents the distal end and aflY the proximal end of the cluster. The A. ochraceoroseus cluster genes demonstrated 62-76% nucleotide identity to their A. nidulans ST cluster gene homologs. Transformation of an A. nidulans aflR mutant with the A. ochraceoroseus aflR restored ST production in A. nidulans transformants. PCR amplification of A. rambellii genomic DNA demonstrated that the AF/ST gene cluster is organized in the same manner as that of A. ochraceoroseus.

BackgroundAspergillus nomius is an opportunistic pathogen and one of the three most important producers of aflatoxins in section Flavi. This fungus has been reported to contaminate agricultural commodities, but it has also been sampled in non-agricultural areas so the host range is not well known. Having a similar mycotoxin profile as A. parasiticus, isolates of A. nomius are capable of secreting B- and G- aflatoxins.ResultsIn this study we discovered that the A. nomius type strain (NRRL 13137) has a genome size of approximately 36 Mb which is comparable to other Aspergilli whose genomes have been sequenced. Its genome encompasses 11,918 predicted genes, 72 % of which were assigned GO terms using BLAST2GO. More than 1,200 of those predicted genes were identified as unique to A. nomius, and the most significantly enriched GO category among the unique genes was oxidoreducatase activity. Phylogenomic inference shows NRRL 13137 as ancestral to the other aflatoxigenic species examined from section Flavi. This strain contains a single mating-type idiomorph designated as MAT1-1.ConclusionsThis study provides a preliminary analysis of the A. nomius genome. Given the recently discovered potential for A. nomius to undergo sexual recombination, and based on our findings, this genome sequence provides an additional evolutionary reference point for studying the genetics and biology of aflatoxin production.