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Abstract
The transfer of genetic information between distantly or even unrelated organisms
during evolution had been inferred from nucleotide sequence comparisons. These studies
provided circumstantial evidence that in rare cases genes had been laterally transmitted
amongst organisms of the domains bacteria, archaea and eukarya. Laboratory-based studies
confirmed that the gene pools of the various domains of organisms are linked. Amongst
the bacterial gene exchange mechanisms transduction, transformation and conjugation,
the latter was identified as the mechanism with potentially the broadest host range
of transfer. Previously, the issue of horizontal gene transfer has become important
in the context of biosafety. Gene transfer studies carried out under more natural
conditions such as in model ecosystems or in the environment established that all
gene transfer mechanisms worked under these conditions. Moreover, environmental hot-spots
were identified where favourable conditions such as nutrient enrichment increased
the probability of genetic exchange among bacteria. In particular, the phytosphere
was shown to provide conducive conditions for conjugative gene exchange. Concern has
been expressed that transfer of recombinant DNA (e.g. antibiotic resistance genes)
from genetically modified organisms (GMOs) such as transgenic plants to phytosphere
bacteria may occur and thus contribute to the undesirable spread of antibiotic resistance
determinants. Studies which were performed to address this issue clearly showed that
such a transfer occurs, if at all, at extremely low frequency.