Substrate Concentration and Plasmid Transfer Frequency between Bacteria in a Model Rhizosphere.

Area of Science:

• Microbial genetics
• Environmental microbiology
• Molecular biology

Background:

• Plasmid transfer is crucial for bacterial adaptation and evolution.
• Understanding factors influencing horizontal gene transfer (HGT) in environments like the rhizosphere is essential.
• Substrate availability can significantly impact microbial interactions and genetic exchange.

Purpose of the Study:

• To investigate the effect of substrate (glucose) concentration on plasmid transfer frequency.
• To elucidate the relationship between nutrient availability and the efficiency of horizontal gene transfer in a controlled model system.
• To determine if plasmid transfer is stimulated by nutrient scarcity or inhibited by nutrient abundance.

Main Methods:

• Utilized a physical model simulating the rhizosphere with hollow fiber membranes.
• Varied substrate (glucose) concentrations to assess impact on plasmid transfer.
• Quantified transconjugant numbers and calculated plasmid transfer frequency.
• Analyzed dependency on donor to recipient ratio, strain distribution, and inoculum density.

Main Results:

• Absolute transconjugant numbers increased with rising glucose concentration.
• Plasmid transfer frequency decreased exponentially with increasing glucose concentration (from 4.4 × 10(-3) to 1.35 × 10(-5)).
• Transfer frequency was dependent on donor/recipient ratio and strain distribution, but independent of inoculum density.

Conclusions:

• High substrate concentrations inhibit plasmid transfer frequency.
• Plasmid transfer appears to be stimulated by scarce growth-limiting nutrients.
• These findings suggest nutrient availability is a key regulator of horizontal gene transfer in microbial communities.