Genomic characterization and fermentation study of the endophyte Stemphylium sp. (Aa22), a producer of bioactive alkyl-resorcinols

Author: mycolabadmin
9/17/2025
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Summary

Scientists have studied a beneficial fungus called Stemphylium sp. Aa22 that lives inside wormwood plants and produces natural insect-repelling compounds called alkyl-resorcinols. By reading the complete genetic code of this fungus, researchers identified the gene responsible for making these compounds and found that growing the fungus in liquid culture produces more of the desired compounds than growing it on solid rice. This research could lead to developing natural, environmentally-friendly pesticides to protect crops from aphids and other pests.

Background

Endophytic fungi are microorganisms that live within plant tissues without causing damage and produce diverse bioactive metabolites with potential as biopesticides. The endophytic fungus Stemphylium sp. strain Aa22, isolated from wormwood (Artemisia absinthium), has been previously reported to produce bioactive alkyl-resorcinols including stemphol and stempholones A and B with antifeedant properties against aphids.

Objective

This study aimed to characterize the genome of Stemphylium sp. Aa22 to clarify its taxonomic placement and identify biosynthetic gene clusters responsible for alkyl-resorcinol production. Additionally, the research evaluated different fermentation conditions (solid rice media and liquid PDB medium with or without talcum powder) to optimize production of these bioactive compounds.

Results

Phylogenomic analysis placed strain Aa22 close to Stemphylium lycopersici with 100% bootstrap support. A 34.1 Mb near-complete genome was assembled with 96.5% BUSCO completeness. Thirty-eight biosynthetic gene clusters were identified, including a single type III polyketide synthase (T3PKS) likely responsible for alkyl-resorcinol biosynthesis. PDB liquid fermentation produced the highest extract yields with high levels of stempholone A and two unidentified metabolites, while talcum powder addition suppressed stempholone A production and reduced chemical diversity.

Conclusion

The genome sequence and phylogenomic analysis clarified that Stemphylium sp. Aa22 is closely related to S. lycopersici. The identified T3PKS gene is a promising target for future manipulation to enhance production of bioactive alkyl-resorcinols. Liquid PDB fermentation without talcum powder proved optimal for producing the target bioactive compounds, with further optimization needed to maximize biosynthetic potential and enable industrial scale-up.

Published in:PLoS One,
Study Type:Genomic and Fermentation Study,
Source: 10.1371/journal.pone.0323031; PMID: 40961083