Plasmids do not consistently stabilize cooperation across bacteria but may promote broad pathogen host-range

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Horizontal gene transfer (HGT) via plasmids is hypothesized to promote bacterial cooperation by converting 'cheats' into cooperators.
• Previous theoretical, genomic, and experimental studies have provided some support for this hypothesis.

Purpose of the Study:

• To investigate the association between genes for extracellular proteins (potential cooperative public goods) and plasmid carriage in bacteria.
• To determine if cooperative genes are more prevalent on higher-transfer-rate plasmids.
• To explore the role of HGT in the long-term maintenance of bacterial cooperation.

Main Methods:

• Comparative analysis of gene distribution across 51 diverse bacterial species.
• Theoretical modeling of HGT dynamics and cooperation.
• Examination of plasmid-borne extracellular protein genes in relation to pathogenicity and host range.

Main Results:

• Genes for extracellular proteins were not more likely to be found on plasmids compared to chromosomes.
• These genes were not preferentially located on plasmids with higher transfer rates.
• Theoretical modeling indicated HGT aids initial invasion but has less impact on long-term cooperation maintenance.
• Extracellular protein genes were more frequently plasmid-borne in pathogenic bacteria with broad host ranges, particularly when encoding virulence traits.

Conclusions:

• HGT via plasmids is not a primary driver for the widespread maintenance of bacterial cooperation.
• Plasmid carriage of extracellular protein genes is associated with bacterial pathogenicity and virulence, rather than general cooperative behaviors.
• The role of plasmids in bacterial evolution appears more linked to virulence factor dissemination in specific ecological niches.