First report on the metabolic characterization of Sterigmatocystin production by select Aspergillus species from the Nidulantes section in Foeniculum vulgare

Inhibitor of Chromosome Segregation in Pseudomonas aeruginosa from Fungal Extracts

Chromosome segregation is an essential cellular process that has the potential to yield numerous targets for drug development. This pathway is presently underutilized partially due to the difficulties in the development of robust reporter assays suitable for high throughput screening. In bacteria, chromosome segregation is mediated by two partially redundant systems, condensins and ParABS. Based on the synthetic lethality of the two systems, we developed an assay suitable for screening and then screened a library of fungal extracts for potential inhibitors of the ParABS pathway, as judged by their enhanced activity on condensin-deficient cells. We found such activity in extracts of Humicola sp. Fractionation of the extract led to the discovery of four new analogues of sterigmatocystin, one of which, 4-hydroxy-sterigmatocystin (4HS), displayed antibacterial activity. 4HS induced the phenotype typical for parAB mutants including defects in chromosome segregation and cell division. Specifically, bacteria exposed to 4HS produced anucleate cells and were impaired in the assembly of the FtsZ ring. Moreover, 4HS binds to purified ParB in a ParS-modulated manner and inhibits its ParS-dependent CTPase activity. The data describe a small molecule inhibitor of ParB and expand the known spectrum of activities of sterigmatocystin to include bacterial chromosome segregation.

Glass bead system to study mycotoxin production of Aspergillus spp. on corn and rice starches

Mycotoxin production by aflatoxin B1 (AFB1) -producing Aspergillus flavus Zt41 and sterigmatocystin (ST) -hyperproducer Aspergillus creber 2663 mold strains on corn and rice starch, both of high purity and nearly identical amylose-amylopectin composition, as the only source of carbon, was studied. Scanning electron microscopy revealed average starch particle sizes of 4.54 ± 0.635 µm and 10.9 ± 2.78 µm, corresponding to surface area to volume ratios of 127 1/µm for rice starch and 0.49 1/µm for corn starch. Thus, a 2.5-fold difference in particle size correlated to a larger, 259-fold difference in surface area. To allow starch, a water-absorbing powder, to be used as a sole food source for Aspergillus strains, a special glass bead system was applied. AFB1 production of A. flavus Zt41 was determined to be 437.6 ± 128.4 ng/g and 90.0 ± 44.8 ng/g on rice and corn starch, respectively, while corresponding ST production levels by A. creber 2663 were 72.8 ± 10.0 µg/g and 26.8 ± 11.6 µg/g, indicating 3-fivefold higher mycotoxin levels on rice starch than on corn starch as sole carbon and energy sources. KEY POINTS: • A glass bead system ensuring the flow of air when studying powders was developed. • AFB1 and ST production of A. flavus and A. creber on rice and corn starches were studied. • 3-fivefold higher mycotoxin levels on rice starch than on corn starch were detected.

StcU-2 Gene Mutation via CRISPR/Cas9 Leads to Misregulation of Spore-Cyst Formation in Ascosphaera apis

Ascosphaera apis is the causative agent of honey bee chalkbrood disease, and spores are the only known source of infections. Interference with sporulation is therefore a promising way to manage A. apis. The versicolorin reductase gene (StcU-2) is a ketoreductase protein related to sporulation and melanin biosynthesis. To study the StcU-2 gene in ascospore production of A. apis, CRISPR/Cas9 was used, and eight hygromycin B antibiotic-resistant transformants incorporating enhanced green fluorescent protein (EGFP) were made and analyzed. PCR amplification, gel electrophoresis, and sequence analysis were used for target gene editing analysis and verification. The CRISPR/Cas9 editing successfully knocked out the StcU-2 gene in A. apis. StcU-2 mutants had shown albino and non-functional spore-cyst development and lost effective sporulation. In conclusion, editing of StcU-2 gene has shown direct relation with sporulation and melanin biosynthesis of A. apis; this effective sporulation reduction would reduce the spread and pathogenicity of A. apis to managed honey bee. To the best of our knowledge, this is the first time CRISPR/Cas9-mediated gene editing has been efficiently performed in A. apis, a fungal honey bee brood pathogen, which offers a comprehensive set of procedural references that contributes to A. apis gene function studies and consequent control of chalkbrood disease.