RP4 Plasmid Transfer Among Strains of Pseudomonas in a Biofilm Reactor

EPA Grant Number: U914730
Title: RP4 Plasmid Transfer Among Strains of Pseudomonas in a Biofilm Reactor
Investigators: Ehlers, Laura J.
Institution: The Johns Hopkins University
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 1995 through January 1, 1996
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1995) Recipients Lists
Research Category: Biology/Life Sciences , Fellowship - Microbiology , Academic Fellowships


The objective of this research project is to observe and quantify conjugation between bacteria growing in a biofilm reactor.


The reactor was chosen for its experimental flexibility and simple mathematical description. Several environmental parameters were varied to determine their influence on transfer frequencies. Finally, a predictive biofilm model was evaluated for its ability to accurately represent plasmid transfer events.

Expected Results:

Conjugation of the broad host range plasmid RP4 between two strains of Pseudomonas occured in the biofilm reactor at high frequencies. The most important environmental parameter was the shear stress at the biofilm-liquid interface. Conjugation was only observed below a shear of 0.0851 N/m2, corresponding to a laminar flow regime. Increasing temperature from 15°C to 28°C increased conjugation frequencies 10,000-fold. Conjugation frequency was unchanged in experiments conducted with 3.5, 7, and 35 mg/L acetate, although total cell concentration in the biofilm increased as expected. Finally, the addition of a sublethal kanamycin concentration affected both the recipient and transconjugant populations, either by enhancing conjugation or providing a selective advantage for transconjugant growth. These data suggest ways to manipulate environmental parameters to increase or decrease plasmid transfer rates among biofilm bacteria.

Supplemental Keywords:

fellowship, biofilm reactor, environmental parameters, DNA, genetically engineered microorganisms, GEMs, environment, conjugation, bacteria, Pseudomonas., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Genetics, Monitoring/Modeling, Environmental Microbiology, Biology, model-based analysis, biofilm dynamics, bacteria monitoring, plasmid transfer, conjugation, biochemistry

Progress and Final Reports:

  • Final