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EC-sponsored Research on Safety of Genetically Modified Organisms - A Review of Results
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image Mobile elements contribution to bacterial adaptability and diversity (MECBAD)

Background and objectives (1)

The transfer of genetic material between organisms is of key importance in understanding the impact of genetically modified organisms on the community and environment. Mobile genetic elements (MGEs) endow their host bacteria with genetic variability and flexibility in response to environmental stress. Horizontal gene exchange by MGEs can be considered as a natural phenomenon for bacterial adaptation and for successful colonization of ecological niches. MGEs are clearly relevant to the issue of introduced genetic information. Despite this, and the importance of MGEs for understanding bacterial diversity and fluctuations of bacterial populations in response to changing environments, our present knowledge is extremely limited, due to an inability to culture the vast majority of bacteria found in the environment.

In this project, groups working on the molecular biology and ecology of MGEs, link their expertise to address the following five key objectives: to gain a better understanding of the diversity and prevalence of MGEs in natural bacterial communities; to improve the basic understanding of what determines the maintenance of MGEs in bacterial populations under environmental conditions; to extend our knowledge of the molecular biology of transfer functions and environmental factors which stimulate or limit transfer of MGEs; to better understand gene acquisition and the spread of novel traits by MGEs; to provide new tools for the biotechnological exploitation of MGEs.

(1) This project was a direct follow-on from the ESF network on molecular biology and ecology of plasmid-mediated gene transfer (network no 44).


Approach and methodology

Detailed descriptions are available at http://mecbad.bba.de. In brief, we used genetically modified host plants and standard molecular biology techniques to identify plasmid transfer and the presence of particular plasmids by plant screening. A particularly important strength of the concerted action is the close link between the molecular biology and ecology of mobile genetic elements. In addition, four workshops are being held focusing on specific aspects which relate to different studies.
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Main findings and outcome

The first MECBAD Symposium (Mont Ste Odile, 23-27 April, 1999) demonstrated very impressively, the large intellectual contribution of the numerous research groups working on the contribution of MGEs to bacterial adaptability and diversity. Several important findings related to biosafety were reported at the meeting.

Firstly, the application of new approaches and tools to study the prevalence and diversity of plasmids has shown that bacteria in different environments carry MGEs which are often difficult to classify with currently available molecular tools. Secondly, genetically modified organisms (GMOs) released into the environment can acquire plasmids in situ and thus contribute to an altered host fitness. Thirdly, plasmids with a broad host range and gene-mobilising capacity could be detected using exogenous isolation techniques in many environments. Fourthly, the application of MGE-specific primers to total DNA from an ecosystem, greatly facilitated the screening of different environments for the presence of specific plasmids, showing an apparent correlation between selective pressure and the prevalence of MGEs, such as IncPß-plasmids. Furthermore, sequencing of newly isolated plasmids showed that replicons often consist of modules which are related to known systems. Sequencing of a cryptic broad-host range plasmid with high gene-mobilising and retromobilising activity was performed. Ecophysiology of the plasmid host was shown to be of importance for the prediction of transfer frequencies under environmental conditions.

Transfer of the Ti plasmid between Agrobacteria is regulated by quorum sensing, creating a need to understand the conditions and signalling involved in different MGE transfer systems. It was also shown that bacteria evolve rapidly where growth rates are relatively high and gene transfer occurs readily. Studies of antibiotic resistance gene dissemination prove that horizontal gene transfer is a highly efficient method for bacteria to acquire advantageous genes. Even when selection pressure is removed, antibiotic resistance genes remain associated with MGE. Broad-host range plasmids such as IncPß-plasmids carrying degradative genes can be introduced to polluted sites to seed catabolic genes amongst the indigenous bacterial populations.

Finally, antibiotic resistance genes used as markers in transgenic crops are unlikely to contribute significantly to the spread of antibiotic resistance in bacterial populations. This is based on the fact that antibiotic resistance genes, often located on MGEs, are already widespread in bacterial populations and that transfer from transgenic plants to bacteria is thought to occur at extremely low frequencies. Control of the antibiotic resistance problem very clearly lies in a reduction of selective pressure by prudent use of antibiotics.
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Conclusions

MGE endow their bacterial host with genetic variability and flexibility, promoting genome plasticity by DNA rearrangements within a bacterium as well as gene exchange between bacteria. Traits specified by MGEs include resistance to antibiotics, heavy metals, radiation, symbiotic or virulence, bidegradation of xenobiotic compounds. Knowledge of MGEs can be exploited by industry, agriculture or medicine. The potential of MGE for biotechnology but also their enormous contribution to bacterial diversity justifies further research on MGE. Environmental factors stimulating horizontal gene transfer processes need to be better understood in order to inhibit gene exchange (e.g. of antibiotic resistance genes or transgenic DNA) or to stimulate the spread of MGE (e.g. to disseminate biodegradative genes in natural populations). A better understanding of the diversity, maintenance and transfer functions of MGE, the acquisition and spread of new phenotypic traits will provide an important scientific basis for future GMO applications and biosafety evaluations and thus will support science-based decision making.


Major publications

Greated A., Thomas C.M., “A pair of PCR primers for IncP-9 plasmids”.
Microbiol., 145, 1999, p. 3003.

Thomas C.M., Smalla K., “Trawling the horizontal gene pool”.
Microbiology-Today,
27, 2000, p. 24.

Smalla K., Krögerrecklenfort E., Heuer H., Dejonghe W., Top E., Osborn M., Niewint J., Tebbe C.C., Barr, Bailey M., Greated A., Thomas C.M., Turner S., Young P., Nikolaopoulou D., Karagouni A., Wolters A., van Elsas J.D., Drønen K., Sandaa R., Borin S., Brabhu J., Grohmann E., Sobecky P., “PCR-based detection of mobile genetic elements in total community DNA”.
Microbiol.,
146, 2000, p. 2.

Hoffmann A., Thimm T., Tebbe C.C., “Fate of plasmid-bearing, luciferase marker gene tagged bacteria after feeding to the soil micro-arthropod Onychiurus fimatus (Collembola)”.
FEMS Microbiol. Ecol.,
30, 1999, p. 125.

Thomas C.M. (ed), The horizontal gene pool: Bacterial plasmids and gene spread, Harwood Academic Publishers, 2000.
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imageConcerted action
 

Contract number
BIO4-CT98-0099

Period
October 1998 - September 2000

Coordinator
K. Smalla
Federal Biological Research Centre for Agriculture and Forestry
Braunschweig (DE)

Project website address
http://mecbad.bba.de

 
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Partners


G. Koraimann
Karl-Franzens-Universität Graz (AT)

M. Thilly-Couturier
Université Libre de Bruxelles (BE)

J. Mahillon
UCL
Louvain-la-Neuve (BE)

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

E. Top
University of Ghent (BE)

J.W. Lengeler
Universität Osnabrück (DE)

G. Muth
Eberhard-Karls-Universität Tübingen (DE)

A. Pühler
Universität Bielefeld (DE)

E. Lanka
Max-Planck-Institut für Molekulare Genetik
Berlin (DE)

M. Strätz
National Research Centre for Biotechnology (GBF)
Braunschweig (DE)

C. Tebbe
Bundesforschungsanstalt für Landwirtschaft (FAL)
Braunschweig (DE)

E. Tietze
Robert Koch Institut
Wernigerode (DE)

K. Gerdes
Odense University (DK)

S. Molin
Technical University of Denmark
Lyngby (DK)

J.C. Alonso
Centro Nacional de Biotecnología (CNB)
Madrid (ES)

F. de la Cruz
Universidad de Cantabria
Santander (ES)

M. Espinosa,
R. Díaz Orejas

Centro de Investigaciones Biológicas
Madrid (ES)

M. Blot
Université Joseph Fourier
Grenoble (FR)

M-C. Lett
Université Louis Pasteur
Strasbourg (FR)

P. Simonet
Université de Lyon
Villeurbanne (FR)

M.J. Bailey
Natural Environment Research Council (NERC)
Oxford (UK)

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

P. Hirsch
IACR-Rothamsted
Harpenden (UK)

P.J. McDermott
Staffordshire University
Stoke on Trent (UK)

R. Pickup
Institute of Freshwater Ecology
Ambleside (UK)

H. Richards
University College London (UK)

J.R. Saunders
University of Liverpool (UK)

C.M. Thomas

The University of Birmingham (UK)

E.M.H. Wellington
University of Warwick
Coventry (UK)

B.M. Wilkins
University of Leicester (UK)

P. Young
The University of York (UK)

C. Drainas
University of Ioannina (GR)

A. Karagouni,
M.A. Typas

University of Athens (GR)

C. Adley,
T. Pembroke

University of Limerick (IE)

L. Dijkhuizen
University of Groningen (NL)

J.D. van Elsas
Plant Research International (formerly IPO-DLO)
Wageningen (NL)

R-A. Sandaa
University of Bergen (NO)

M. Hermansson
Göteborg University (SE)

J. Nesvera
Academy of Sciences of the Czech Republic
Praha (CZ)

P. Ceglowski
Institute of Biochemistry and Biophysics
Warsaw (PL)

M. Wlodarczyk
Warsaw University (PL)

 
 
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