Genus-wide analysis of Fusarium polyketide synthases reveals broad chemical potential.

The genus Fusarium includes pathogens of global concern to animal and plant health. Natural products (NPs) synthesized by Fusarium can contribute to pathogenesis or competitiveness of the fungus in the environment and to animal diseases, including cancer and neural tube defects. Polyketide synthases (PKSs) are a family of large, multi-domain enzymes that are required for synthesis of most fungal NPs. To gain insight into the NP potential of Fusarium, we retrieved 2974 PKS gene sequences from the genomes of 206 Fusarium species. Phylogenetic analysis resolved these PKSs, along with 118 previously described PKSs from other fungi, into 123 clades. Based on results from previous studies, we propose that PKSs in the same clade generally synthesize the same polyketide, which is structurally distinct from polyketides synthesized by PKSs in other clades. We predict that the 123 clades potentially produce 113 structurally distinct families of polyketide-derived NPs because some NPs (e.g., zearalenone) require two PKSs for their synthesis. Collectively, the clades include PKSs required for synthesis of six NPs whose production has not previously been reported in Fusarium, including two NPs with significant pharmaceutical interest: chaetoviridin and a statin. Our results highlight the NP diversity of Fusarium and the potential of the genus to produce metabolites with medical and other applications.

Fusarium chaquense, sp. nov, a novel type A trichothecene-producing species from native grasses in a wetland ecosystem in Argentina.

The Chaco wetland is among the most biologically diverse regions in Argentina. In collections of fungi from asymptomatic native grasses (Poaceae) from the wetlands, we identified isolates of Fusarium that were morphologically similar to F. armeniacum, but distinct from it by their production of abundant microconidia. All the isolates had identical, or nearly identical, partial sequences of TEF1 and RPB2. But they were distinct from reference sequences from F. armeniacum and Fusarium species closely related to it. Phylogenetic analysis of 34 full-length housekeeping gene sequences retrieved from whole genome sequences of three Chaco wetland isolates, 29 genes resolved the isolates as an exclusive clade within the F. sambucinum species complex. Based on results of the morphological and phylogenetic analysis, we concluded that the Chaco wetland isolates are a distinct and novel species, herein described as Fusarium chaquense, sp. nov., which is closely related to F. armeniacum. F. chaquense in culture can produce the trichothecenes T-2 and HT-2 toxin, neosolaniol, diacetoxyscirpenol, and monoacetoxyscirpenol, as well as beauvericin and the pigment aurofusarin. Genome sequence analysis also revealed the presence of three previously described loci required for trichothecene biosynthesis. This research represents the first study of Fusarium in a natural ecosystem in Argentina.

A PCR method to identify ochratoxin A-producing Aspergillus westerdijkiae strains on dried and aged foods.

Ochratoxins are a group of mycotoxins that frequently occur as contaminants in agricultural commodities and foods, including dry-cured meats and cheeses. The fungus Aspergillus westerdijkiae is frequently isolated from aged foods and can produce ochratoxin A (OTA). However, individual strains of the fungus can have one of two OTA production phenotypes (chemotypes): OTA production and OTA nonproduction. Monitoring and early detection of OTA-producing fungi in food are the most effective strategies to manage OTA contamination. Therefore, we examined genome sequence data from five A. westerdijkiae strains isolated from the surface of cheese from southern Italy to identify genetic markers indicative of the twoOTA chemotypes. This analysis revealed a naturally occurring deletion of the OTA regulatory gene, otaR, in an OTA-nonproducing isolate.We used this information to design a polymerase chain reaction (PCR) method that could identify A. westerdijkiae and distinguish between the two OTA chemotypes. In this method, the PCR primers were complementary to conserved sequences flanking otaR and yielded different-sized amplicons from strains with the different chemotypes. The primers did not yield ota-region-specific amplicons from other OTA-producing species. Because the method is specific to A. westerdijkiae and can distinguish between the two OTA chemotypes, it has potential to significantly improve OTA monitoring programs.