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Fruiting body-associated Pseudomonas contact triggers ROS-mediated perylenequinone biosynthesis in Shiraia mycelium
Yan Jun Ma1, Xin Ping Li2, Jia Hui Li1
1College of Life Sciences, Northwest Normal University, Lanzhou, China.
Abstract:
Perylenequinones (PQs) from Shiraia fruiting bodies serve as potent photosensitizers for anticancer and antimicrobial photodynamic therapy (PDT). Although these fruiting bodies harbor diverse endophytic bacteria, their interactions with the host fungus remain poorly understood. In this study, we used an in vitro confrontation bioassay to investigate the interaction between Shiraia sp. S9 and dominant Pseudomonas isolates, analyzing fungal transcriptional responses and PQ biosynthesis. Comparative assessment of co-cultures with freely suspended live P. fulva SB1 versus dialysis membrane-separated bacteria revealed that direct physical contact is essential for eliciting fungal PQ production, particularly extracellular secretion of hypocrellin A (HA), HC, and elsinochrome A-C. Bacterial elicitation with P. fulva SB1 at 400 cells/mL stimulated both intracellular PQ biosynthesis and extracellular secretion, resulting in a total PQ yield of 362.2 mg/L, a 2.4-fold increase over axenic cultures. RNA-seq analysis after 24 h of co-culture identified 646 differentially expressed genes (DEGs), with 445 upregulated and 201 downregulated, showing significant enrichment in oxidative stress defense, carbohydrate metabolism, and membrane transport functions. Bacterial contact induced reactive oxygen species (ROS) generation, specifically O2·- and H2O2, which mediated increased membrane permeability and enhanced HA production. This was achieved through upregulation of key genes involved in central carbon metabolism, polyketide synthase (PKS) for PQ biosynthesis, and major facilitator superfamily (MFS) transporter for PQ exudation. Our work provides the first evidence that the contact-dependent ROS signaling by endophytes within fruiting bodies regulates fungal secondary metabolism, offering novel insights into bacterial-fungal interactions and establishing an effective co-culture strategy for enhanced production of bioactive PQs.
Insights
Bacterial contact with Shiraia fungus triggers perylenequinone (PQ) production via reactive oxygen species (ROS). This interaction enhances PQ biosynthesis and secretion, offering a new strategy for producing these valuable compounds.
Area of Science:
- Microbiology
- Mycology
- Biochemistry
Background:
- Perylenequinones (PQs) are potent photosensitizers used in photodynamic therapy (PDT).
- Shiraia fungi produce PQs, but their biosynthesis is influenced by endophytic bacteria, though interactions are poorly understood.
Purpose of the Study:
- To investigate the interaction between Shiraia sp. S9 and Pseudomonas bacteria.
- To analyze fungal transcriptional responses and PQ biosynthesis regulation by bacteria.
- To establish an effective co-culture strategy for enhanced PQ production.
Main Methods:
- In vitro confrontation bioassay comparing direct contact vs. separated co-cultures.
- Quantification of PQ production (hypocrellin A, HC, elsinochrome A-C).
- RNA-sequencing (RNA-seq) to analyze fungal gene expression.
- Measurement of reactive oxygen species (ROS) generation.
Main Results:
- Direct bacterial contact is essential for eliciting fungal PQ production and extracellular secretion.
- Co-culture with Pseudomonas fulva SB1 increased total PQ yield by 2.4-fold.
- Bacterial contact induced ROS (O2•−, H2O2), upregulating genes for metabolism, PQ biosynthesis (PKS), and transport (MFS).
Conclusions:
- Contact-dependent ROS signaling by endophytes regulates fungal secondary metabolism (PQ production).
- This study provides novel insights into bacterial-fungal interactions.
- An effective co-culture strategy for enhanced bioactive PQ production was established.
