Microbial Species Coexistence Depends on the Host Environment

Area of Science:

• Microbiology
• Ecology
• Symbiosis

Background:

• Organisms and their microbial communities form complex ecosystems where bacterial composition impacts host health.
• The processes driving microbial community structure and stability remain largely unknown.
• The freshwater polyp Hydra harbors a simple microbiome, making it an ideal model for studying microbial interactions.

Purpose of the Study:

• To investigate the environmental factors influencing microbial community composition and stability.
• To deconstruct the microbiome of Hydra and understand the interactions between its dominant bacterial associates, Curvibacter and Duganella.
• To determine if host-specific environments are necessary for stable microbial coexistence.

Main Methods:

• Comparative analysis of Curvibacter and Duganella performance in germfree Hydra hosts versus two in vitro environments.
• Tracking species frequencies and abundances over time under different conditions.
• Investigating the role of direct contact and secretions in microbial competition.

Main Results:

• Stable coexistence of Curvibacter and Duganella was observed exclusively in the host environment.
• Duganella outcompeted Curvibacter in both in vitro conditions, regardless of initial frequencies.
• Duganella's competitive advantage involved secretions from Curvibacter and direct contact, with spatial distribution potentially mitigating competition in the host.

Conclusions:

• Host-specific environments are critical for maintaining stable microbial community structures and species coexistence.
• In vitro systems may not accurately replicate the complex interactions governing natural microbiomes.
• Rare microbial members may play a significant role in achieving native community composition and carrying capacity.