Dissecting two contrasting phytoplankton-symbiont interaction modes based on population dynamics and gene expression...

Area of Science:

• Microbiology
• Ecology
• Systems Biology

Background:

• Microbial symbionts are crucial for host health and ecosystem dynamics.
• Understanding host-microbe interactions is key to deciphering microbiome structure.
• Host-microbe interactions can be simplified into unidirectional and bidirectional modes.

Purpose of the Study:

• To investigate how distinct host-microbe interaction modes (unidirectional vs. bidirectional) influence symbiont strategies and microbiome assembly.
• To test the hypothesis that symbionts are maintained via a trade-off between utilizing host-derived dissolved organic matter (DOM) or engaging in feedback interactions.
• To examine the growth and gene expression responses of representative symbionts and their host under different interaction modes.

Main Methods:

• Screening of symbionts isolated from the host *C. sorokiniana*.
• Culturing and analysis of two representative symbionts (*Curvibacter* sp. and *Falsiroseomonas* sp.) and the host under axenic and co-cultured conditions.
• Measurement of symbiont growth and host/symbiont gene expression profiles under unidirectional and bidirectional interaction modes.

Main Results:

• *Curvibacter* sp. thrived via unidirectional interaction, utilizing host-derived DOM.
• *Falsiroseomonas* sp. grew best via bidirectional interaction with live host cells, showing greater gene expression shifts.
• Host response to *Falsiroseomonas* sp. included reduced growth and altered nitrogen-rich amino acid metabolism, potentially benefiting the symbiont.

Conclusions:

• Distinct host-microbe interaction modes drive differential symbiont strategies, impacting microbiome assembly.
• The findings explain how functionally diverse microbial assemblages are maintained within hosts.
• Understanding these interaction modes is fundamental for microbiome research, management, and engineering.