Microbial diversification is maintained in an experimentally evolved synthetic community.

Area of Science:

• Microbial Ecology
• Evolutionary Biology
• Bacteriology

Background:

• Bacteria in nature exist in complex communities and engage in interactions like cross-feeding.
• The impact of these interactions on bacterial diversification patterns is not well understood.

Purpose of the Study:

• To investigate how cross-feeding interactions with *Acinetobacter johnsonii* influence the diversification of *Pseudomonas putida*.
• To compare the evolutionary trajectories of *P. putida* in monoculture versus co-culture.

Main Methods:

• Experimental evolution of *P. putida* in monoculture and co-culture with *A. johnsonii* for 200 generations.
• Genomic analysis to identify mutations, including those in the *fleQ* gene.
• Invasion experiments and evolutionary 'replay' experiments to assess coexistence dynamics.

Main Results:

• *P. putida* diversified into two morphotypes in co-culture, differing by single-point mutations, including in *fleQ*.
• Mutations leading to altered motility and biofilm formation, such as in *fleQ*, swept to fixation in monocultures but not in co-cultures.
• *Acinetobacter johnsonii* presence stabilized the coexistence of the two *P. putida* morphotypes.

Conclusions:

• Interspecies interactions, specifically cross-feeding, significantly shape microbial diversification patterns.
• The presence of a cross-feeding partner can prevent the fixation of certain mutations and promote the stable coexistence of distinct lineages.
• These findings highlight the importance of considering species interactions in understanding microbial community evolution.