Comparative genome sequencing reveals chemotype-specific gene clusters in the toxigenic black mold Stachybotrys

Abstract

BackgroundThe fungal genus Stachybotrys produces several diverse toxins that affect human health. Its strains comprise two mutually-exclusive toxin chemotypes, one producing satratoxins, which are a subclass of trichothecenes, and the other producing the less-toxic atranones. To determine the genetic basis for chemotype-specific differences in toxin production, the genomes of four Stachybotrys strains were sequenced and assembled de novo. Two of these strains produce atranones and two produce satratoxins.ResultsComparative analysis of these four 35-Mbp genomes revealed several chemotype-specific gene clusters that are predicted to make secondary metabolites. The largest, which was named the core atranone cluster, encodes 14 proteins that may suffice to produce all observed atranone compounds via reactions that include an unusual Baeyer-Villiger oxidation. Satratoxins are suggested to be made by products of multiple gene clusters that encode 21 proteins in all, including polyketide synthases, acetyltransferases, and other enzymes expected to modify the trichothecene skeleton. One such satratoxin chemotype-specific cluster is adjacent to the core trichothecene cluster, which has diverged from those of other trichothecene producers to contain a unique polyketide synthase.ConclusionsThe results suggest that chemotype-specific gene clusters are likely the genetic basis for the mutually-exclusive toxin chemotypes of Stachybotrys. A unified biochemical model for Stachybotrys toxin production is presented. Overall, the four genomes described here will be useful for ongoing studies of this mold’s diverse toxicity mechanisms.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-590) contains supplementary material, which is available to authorized users.

Diversity and evolution of polyketide biosynthesis gene clusters in the Ceratocystidaceae

“…Despite the fact that PKS-III is not generally known from the fungi, all of the Ceratocystidaceae genomes that were examined here showed a highly conserved cluster that contained a homolog of the gene encoding chalcone synthase A (CHS). This cluster was also very similar to that reported in Stachybotrys chlorohalonata (Semeiks et al 2014). Few studies have examined the role of this enzyme in fungi, but expression analyses have revealed that all of the PKS-III genes examined so far, are responsible for the biosynthesis of polyketide pyrones and resorcinols (Hashimoto et al 2014).…”

Truncated satratoxin gene clusters in selected isolates of the atranone chemotype of Stachybotrys chartarum (Ehrenb.) S. Hughes

“…Comparison of the genomes of three S. chartarum strains representing both chemotypes as well as one strain of S. chlorohalonata revealed the presence of common, but also of chemotype-specific, gene clusters. These were attributed to the biosynthesis of satratoxins and atranones, respectively (Semeiks et al 2014). Two isolates of S. chartarum (IBT 7711 and IBT 40293) produced macrocyclic trichothecenes and contained genes that were suggested to be involved in the respective biosynthetic pathway.…”

Aspergillus hancockii sp. nov., a biosynthetically talented fungus endemic to southeastern Australian soils

“…Relatively few biosynthetic gene clusters for trichothecenes have been described from fungi other than Fusarium species, notable examples being from Trichoderma and Stachybotrys species [49, 50]. The A .…”