Antagonistic interactions subdue inter-species green-beard cooperation in bacteria

Area of Science:

• Microbial Ecology
• Evolutionary Biology
• Bacterial Cooperation

Background:

• The green-beard mechanism theoretically promotes cooperation by linking cooperative traits with recognition markers.
• This mechanism is proposed to facilitate cooperation even among genetically unrelated individuals.

Purpose of the Study:

• To investigate the green-beard mechanism for cooperation between two unrelated bacterial species, Pseudomonas aeruginosa and Burkholderia cenocepacia.
• To determine if shared iron-scavenging siderophore (pyochelin) production and uptake can foster interspecies cooperation.

Main Methods:

• Co-culture experiments were performed with P. aeruginosa and B. cenocepacia under iron-limited conditions.
• Analysis of pyochelin exchange and its fitness benefits in cell-free supernatants and co-cultures.
• Assessment of competitive interactions and dominance dynamics within the mixed communities.

Main Results:

• Pyochelin was mutually exchanged between species, providing fitness benefits under iron limitation in isolation.
• In co-culture, cooperative benefits were negated, with P. aeruginosa dominating the community.
• P. aeruginosa exhibited interference competition, suppressing B. cenocepacia growth.

Conclusions:

• Interspecies cooperation mediated by the green-beard mechanism (pyochelin sharing) was undermined by competition.
• Genome-level conflicts and interference competition overruled aligned interests at the cooperative locus.
• The evolution and maintenance of interspecific siderophore cooperation are challenging due to competitive interactions.