Plasmid Conjugation in an Activated Sludge Microbial Community

Abstract Horizontal genetic transfer (HGT) events are thought to play an important role in the development of microbial species capable of degrading toxic contaminants. The goal of the present study was to determine the effect of relative cell density between the donor and recipient cells for HGT conjugation events in a mixed microbial community. Specifically, the transfer of the TOL plasmid pWWO from Pseudomonas putida BBC443 to micro-organisms present in the activated sludge obtained from a wastewater treatment plant in Durham, NC was investigated. Inocula with cell concentrations ranging from 1:1 to 20:1 (activated sludge to P. putida BBC443) were investigated. The TOL plasmid pWWO contains a gene encoding a green fluorescent protein (gfp), which is only expressed following a conjugation event. Thus, fluorescence measurements can be used to estimate plasmid proliferation. HGT rates were monitored by flow cytometry while toluene degradation profiles were obtained by gas chromatography. Conjugation rates...