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EC-sponsored Research on Safety of Genetically Modified Organisms - A Review of Results
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image Transfer, survival and spread of genetically manipulated organisms (GMOs) in river sediments, soils and agricultural environments

Background and objectives

Genetically engineered micro-organisms (GEMs) are likely to be accidentally released to, or deliberately used in, aquatic or terrestrial habitats. Potential environmental uses of GEMs include waste treatment, detoxification, control of agricultural pests and plant growth stimulation. Little is currently known about gene flow or inoculant survival in natural populations of bacteria so the fate of GEMs or their DNA is unknown. Studies on plasmid transfer and inoculant survival in soil and water are therefore necessary.

This research aimed to study the transfer of natural plasmids, isolated from soil and water, and of recombinant plasmid vectors between species of Escherichia coli, Pseudomonas and Alcaligenes. Heavy metal resistance genes and lactose-utilisation genes were used as markers.

Approach and methodology

Plasmids are self-replicating units of DNA. We investigated the roles of the key genetical and environmental factors that might limit their transfer. Laboratory microcosms were designed to investigate their transfer and survival in water and soil. The survival and mobility of genetically marked plant beneficial pseudomonads was studied in soil microcosms and lysimeters, to simulate an agricultural soil environment. To ensure the validity of the results recently isolated, natural strains of bacteria and plasmids were used. Laboratory and field results were compared whenever possible.

Main findings and outcome

Plasmids were found to transfer actively in the conditions pertaining in soil and river epilithon. Transfer between a wide variety of bacteria, including heterotrophs, sulphate reducing bacteria and cyanobacteria, was shown to be possible. Retrotransfer allowed movement of small recombinant plasmids directly into natural bacterial communities. Plasmids from aquatic bacteria were clearly shown to be able to capture recombinant DNA by retrotransfer. Similarity was demonstrated between plasmid transfer on stones in a stream microcosm and in situ in the river studies. Survival and mobility studies of plant growth beneficial pseudomonads demonstrated that bacteria could survive well in agricultural soils, especially when a dry inoculum was used. Pseudomonad mutants with impaired survival were isolated and shown to have the potential for DNA containment.


Important methodological advances were made in this study. These included a gene escape model which used a transfer proficient E. coli containing a heavy-metal resistance gene cassette, and an efficient marker system for soil pseudomonads with a novel lactose utilisation DNA insert.

The potential for retrotransfer in aquatic bacteria was shown. Likewise, a stream microcosm for simulating plasmid transfer between GEMs on river stones was developed.

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Contract number

January 1989 – December 1990

Follow-up of the project:
This project was continued in EC project: BIOT-CT91-0284



M. Mergeay
Laboratory of Genetics & Biotechnology (SCK/VITO)
Mol (BE)

M.J.T. Carrondo
Instituto de Biologia Experimental e Tecnologica (IBET)
Oeiras (PT)

J.C. Fry
University of Wales
College of Cardiff (UK)

W. Verstraete
University of Ghent (BE)

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