This study was led by Professor Yi Wang and Professor Weiming Zhu from the School of Medicine and Pharmacy, Ocean University of China. Chengfeng Hou, a graduated PhD candidate, and Deng Yu, a current PhD candidate from the same institution, are the co-first authors of the paper with equal contribution.
Monascus pigments (MPs) are important natural polyketide colorants widely used in the food, cosmetic, and daily chemical industries, with additional antibacterial, lipid-lowering, and other bioactivities. However, the industrial application of MPs has long been hindered by three key bottlenecks: unstable yield, poor environmental stability, and the risk of contamination by citrinin, a toxic fungal secondary metabolite. To address these challenges, the team adopted an epigenetic derepression strategy to unlock the hidden biosynthetic potential of MPs in Talaromyces purpurogenus OUCMDZ-019.
Through genome mining, the team first found that the genome of T. purpurogenus OUCMDZ-019 harbors about 80 biosynthetic gene clusters (BGCs) for secondary metabolites, most of which are silent or lowly expressed under standard laboratory culture conditions. The team focused on Ash2, a core subunit of the COMPASS complex responsible for histone H3K4 methylation, a key epigenetic modification regulating gene transcription. They successfully constructed an Ash2 deletion mutant via homologous recombination.
Integrated transcriptomic and metabolomic analysis revealed that Ash2 deletion triggered genome-wide transcriptional reprogramming in the fungus, with a significantly higher number of upregulated genes than downregulated ones. Most critically, the key genes in the MPs-related BGC were markedly upregulated. The metabolic profile of the mutant was drastically remodeled, with MPs-related compounds becoming the dominant differential metabolites, accompanied by a distinct bright red phenotypic change of the strain visible to the naked eye.
To systematically characterize the MPs family activated by Ash2 deletion, the team combined genome mining, transcriptomics, and GNPS molecular networking to construct a global molecular network of the metabolites from the mutant. This allowed them to precisely locate the characteristic metabolite cluster of MPs, and clarify the structural diversification pattern of these compounds centered on orange MPs. Guided by this network-based targeted isolation strategy, the team successfully obtained 12 MPs and related derivatives, including four previously undescribed azaphilone compounds named talarpurpurones A–D. The complete structures and absolute configurations of these new compounds were determined via high-resolution mass spectrometry, multi-dimensional nuclear magnetic resonance spectroscopy, and quantum chemical ECD calculations.
The "congener compositional drift" during MPs fermentation, which causes unstable batch-to-batch product quality, has long been a major pain point for the industry. Using the isolated representative orange MPs as substrates, the team systematically conducted azaphilic addition transformation experiments under varying pH, reaction time, and solvent systems, and clarified the pH-dependent rule of this key reaction. The results showed that the azaphilic addition reaction proceeded much faster under neutral/weak alkaline conditions, while it was significantly inhibited under strong acidic conditions. The team further elucidated the stepwise molecular mechanism of this reaction, providing key experimental evidence for explaining the dynamic changes of pigment components during fermentation.
The team conducted a systematic evaluation of the physicochemical properties and bioactivities of the isolated MPs. The results showed that the new compound talarpurpurone A had an ultra-high color value of 27,520 U/g with outstanding tinting strength. More importantly, it maintained a stable bright red color across an ultra-wide pH range from 3.0 to 11.0, with tinting performance and environmental stability significantly outperforming commercial MPs products. Bioactivity assays revealed that these pigments exhibited moderate inhibitory activity against Gram-positive bacteria including Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and Bacillus subtilis, and some compounds also showed moderate lipid-lowering activity. Notably, both bioinformatic analysis and fermentation experiments confirmed that T. purpurogenus OUCMDZ-019 has no citrinin biosynthetic capacity, eliminating the risk of mycotoxin contamination from the source.
"This study provides a high-quality fungal strain and technical support for the safe industrial production of Monascus pigments, and also establishes an integrated research framework combining epigenetic regulation, multi-omics analysis, and molecular networking for the discovery of novel fungal natural products," the team noted. The findings lay a solid foundation for the green and safe industrialization of natural pigments, and also offer new insights into the epigenetic regulation of fungal secondary metabolism.
See the article:
Chromatin-mediated upregulation of Monascus pigments in Talaromyces purpurogenus OUCMDZ-019 via disruption of Ash2
