Cooperation and conflict in microbial biofilms.

Area of Science:

• Microbiology
• Evolutionary Biology
• Biophysics

Background:

• Biofilms are microbial communities where cells adhere to surfaces and secrete extracellular polymeric substances (EPS).
• EPS is considered a shared resource, implying that biofilm formation relies on high levels of cooperation among cells.
• The evolutionary drivers and social dynamics of EPS production in biofilms remain incompletely understood.

Purpose of the Study:

• To investigate the evolutionary outcome of competition between biofilm strains with varying polymer production levels.
• To determine if cooperation is a necessary factor for the evolution of polymer production in biofilms.
• To model the impact of polymer secretion on biofilm structure and competitive dynamics.

Main Methods:

• Utilized a detailed individual-based simulation of biofilm development.
• Incorporated a biochemical model of carbon fluxes for growth and polymer production.
• Explicitly calculated diffusion-reaction dynamics and solute gradients within the simulated biofilm.

Main Results:

• Extracellular polymer production was found to have a strong evolutionary advantage.
• Polymer secretion, while benefiting a cell's own lineage by improving resource access, can harm neighboring non-producer cells through suffocation.
• This phenomenon, akin to vertical growth, confers a competitive advantage within mixed-genotype biofilms, negating the need for global cooperation.

Conclusions:

• Biofilm polymer secretion is driven by individual lineage advantage rather than group-level cooperation.
• The presence of multiple strains within a biofilm is likely to promote, not inhibit, polymer secretion.
• These findings necessitate a re-evaluation of how biofilms respond to changing social environments and competitive pressures.