Plasmid Transfer in Soil and Rhizosphere

Abstract

Transfer of plasmids pFT30 and RP4 between newly-introduced bacilli and pseudomonads, respectively, is described. In sterile soil, transfer of pFT30 was only detected when exogenous nutrients were added; bentonite clay significantly enhanced the transfer frequency. In nonsterile soil, pFT30 was transferred in the presence but not in the absence of bentonite clay. No transfer was detected in the rhizosphere of wheat. In sterile soil, transfer of RP4 between introduced pseudomonads was detected, and nutrients and bentonite clay both enhanced the transfer frequency. In nonsterile soil, transfer only occurred if exogenous nutrients were added; the transfer frequency was enhanced in bentonite-amended soil. In nutrient-enriched soil, transfer was detected at 15, 20 and 27 °C, but not at 4 and 10 °C. The plasmid transfer frequency was further significantly enhanced in the wheat rhizosphere as compared to transfer in bulk soil.