Chemically-Mediated Interactions Between Macroalgae, Their Fungal Endophytes, and Protistan Pathogens

Area of Science:

• Marine Biology
• Mycology
• Phycology
• Chemical Ecology

Background:

• Filamentous fungi are common endophytes in macroalgae, but their ecological functions are poorly understood.
• The interactions between macroalgae, their fungal endophytes, and protistan pathogens are complex and warrant further investigation.

Purpose of the Study:

• To investigate the protective role of fungal endophyte metabolites against protistan pathogens in macroalgae.
• To identify and characterize bioactive compounds from fungal endophytes with antimicrobial properties.

Main Methods:

• Isolation and identification of cultivable fungal endophytes from four brown algal species using LSU and SSU sequencing.
• Testing fungal metabolomes for their efficacy in reducing pathogen infection in the algal model *Ectocarpus siliculosus*.
• Chemical characterization of active metabolomes and isolation of key inhibitory compounds.

Main Results:

• Metabolites from *Phaeosphaeria* sp. AN596H, specifically pyrenocines, demonstrated broad-spectrum inhibition against oomycetes (*Eurychasma dicksonii*, *Anisolpidium ectocarpii*) and a phytomixid (*Maullinia ectocarpii*).
• These pyrenocines also effectively inhibited infections by *Olpidiopsis pyropiae* and *Pythium porphyrae* in *nori* (*Pyropia yezoensis*).

Conclusions:

• Fungal endophytes associated with brown algae produce bioactive metabolites that confer protection against a range of protistan pathogens.
• These findings suggest a significant role for endophyte-derived compounds in mediating host-pathogen interactions and offer potential applications in marine aquaculture for disease management.