The enhancement of conjugal plasmid pBHR1 transfer between bacteria in the presence of extracellular metabolic products produced by Microcystis aeruginosa

Conjugal plasmid transfer from Escherichia coli S17-1 (pBHR1) to Pseudomonas stutzeri was investigated in the presence of a cyanophyta Microcystis aeruginosa. The plasmid transfer frequency increased with higher densities or ill. aeruginosa. The extracellular metabolic products (EMPs) from M. aeruginosa were found to enhance the plasmid transfer between bacteria. Furthermore. the plasmid transfer frequency in medium containing EMI's was significantly higher than that in culture medium with or without glucose. These results suggest that M. aeruginosa enhances conjugal plasmid transfer between bacteria through its EMPS, and that identity of the carbon Source is ail important factor affecting conjugal plasmid transfer in aquatic environments. (C) 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.