Ruegeria strains promote growth and morphogenesis of the giant coenocytic alga Bryopsis

Area of Science:

• Marine Biology
• Phycology
• Microbial Ecology

Background:

• Giant coenocytes, like Bryopsis algae, are multinucleated single cells that grow without cell division.
• Understanding their morphogenesis and growth mechanisms is crucial for marine biology.
• Microbial associations are known to influence macroalgal development.

Purpose of the Study:

• To investigate the role of associated bacteria in the growth and morphogenesis of the coenocytic macroalga Bryopsis.
• To identify specific bacterial strains that influence Bryopsis development.
• To explore the specificity of bacterial-algal interactions.

Main Methods:

• Isolation and co-culture of bacterial strains with Bryopsis.
• Analysis of conditioned seawater from Ruegeria cultures.
• Seasonal microbiome analysis of Bryopsis associations.
• Comparative co-culture experiments with different Bryopsis strains.

Main Results:

• Four Ruegeria bacterial strains significantly accelerated Bryopsis growth and induced side-branch formation.
• Conditioned seawater from Ruegeria cultures mimicked these growth-promoting effects.
• Ruegeria was consistently associated with cultured Bryopsis, suggesting a symbiotic relationship.
• Bacterial effects on growth and morphogenesis were observed even without Ruegeria detection in all tested Bryopsis strains.

Conclusions:

• Specific bacterial symbionts, such as Ruegeria, play a vital role in promoting the growth and morphogenesis of the coenocytic alga Bryopsis.
• Bryopsis utilizes associated bacteria for development, similar to multicellular algae, but without strict species-specific requirements.
• These findings highlight the ecological importance of bacterial-algal symbiosis in marine ecosystems.