Source-sink plasmid transfer dynamics maintain gene mobility in soil bacterial communities

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Horizontal gene transfer is crucial for bacterial adaptation, with conjugative plasmids mediating gene exchange.
• Plasmids can be unstable in certain bacterial species, leading to loss.
• Alternative hosts can facilitate plasmid persistence through interspecific transfer.

Purpose of the Study:

• To investigate the role of alternative hosts in plasmid population dynamics.
• To understand how interspecific plasmid transfer affects plasmid stability and bacterial evolution.
• To examine the impact of mercury resistance (Hg(R)) plasmid pQBR57 in soil microcosm communities.

Main Methods:

• Established soil microcosm communities with Pseudomonas fluorescens, Pseudomonas putida, and the Hg(R) plasmid pQBR57.
• Utilized both with and without mercury (Hg(II)) selection.
• Employed mathematical modeling and experimental analysis.

Main Results:

• Plasmid pQBR57 was stable in P. fluorescens but lost or chromosomally integrated in P. putida monocultures.
• Interspecific conjugation from P. fluorescens enabled pQBR57 persistence in P. putida via source-sink dynamics.
• Co-culturing slowed the replacement of pQBR57 by chromosomal Hg(R) in P. putida.

Conclusions:

• Interspecific transfer is vital for plasmid survival in hosts that cannot maintain them alone.
• This process broadens community access to the plasmid-borne accessory gene pool.
• Facilitates bacterial evolvability by maintaining gene flow across species.