A transgene-centred approach to the biosafety of transgenic plants: overview of selection and reporter genes

Marker rescue studies of the transfer of recombinant DNA to Streptococcus gordonii in vitro, in foods and gnotobiotic rats

A plasmid marker rescue system based on restoration of the nptII gene was established in Streptococcus gordonii to study the transfer of bacterial and transgenic plant DNA by transformation. In vitro studies revealed that the marker rescue efficiency depends on the type of donor DNA. Plasmid and chromosomal DNA of bacteria as well as DNA of transgenic potatoes were transferred with efficiencies ranging from 8.1 x 10(-6) to 5.8 x 10(-7) transformants per nptII gene. Using a 792-bp amplification product of nptII the efficiency was strongly decreased (9.8 x 10(-9)). In blood sausage, marker rescue using plasmid DNA was detectable (7.9 x 10(-10)), whereas in milk heat-inactivated horse serum (HHS) had to be added to obtain an efficiency of 2.7 x 10(-11). No marker rescue was detected in extracts of transgenic potatoes despite addition of HHS. In vivo transformation of S. gordonii LTH 5597 was studied in monoassociated rats by using plasmid DNA. No marker rescue could be detected in vivo, although transformation was detected in the presence of saliva and fecal samples supplemented with HHS. It was also shown that plasmid DNA persists in rat saliva permitting transformation for up to 6 h of incubation. It is suggested that the lack of marker rescue is due to the absence of competence-stimulating factors such as serum proteins in rat saliva.

Effect of Food Processing on the Fate of DNA with Regard to Degradation and Transformation Capability in Bacillus subtilis

Soymilk, tofu, corn masa, and cooked potato were produced from transgenic raw materials and the effect of processing on the degradation of DNA was studied. Major degrading factors were for soymilk and tofu the mechanical treatment of soaked soybeans and for corn masa and cooked potatoes the thermal treatment. In the processed foods no DNA fragments > 1.1 kb were detected. We included in our studies the effect of the size of donor DNA and length of the homologous sequence on the marker rescue transformation of B. subtilis LTH 5466, which was monitored by restoration of deleted nptII. When DNA fragments (168, 414, 658, and 792 bp) of nptII and linearized plasmid DNA (pGEM-T-1, 3168 bp and pGEM-T-2, 3792 bp) containing the 168 bp or 792 bp fragments, respectively, were used as donor DNA, it was observed that the efficiency of marker rescue decreased with decreasing length of homologous sequence. The use of a larger plasmid (pMR2, 5786 bp) containing the 792 bp fragment revealed higher efficiency of marker rescue compared to pGEM-T-2. The nptII fragments resulted in lower efficiencies compared to plasmid DNA containing the same fragment. For the 792 bp fragment and the linearized plasmid pMR2 a first-order dependency of the frequency of marker rescue transformation on the DNA concentration was observed. Based on the acquired data, the hypothetical frequency of transformation of transgenic DNA to B. subtilis in cooked potatoes was calculated to be equal to 8.5 x 10(-19) and 1.2 x 10(-27) for homologous and illegitimate recombination, respectively. These data permit to roughly estimate the time after which a person (10(8) years) or the world population (15 days) is exposed to one transformant generated by homologous recombination event, when the daily consumption per person is 130 g of cooked potatoes.

The release of genetically modified crops into the environment. Part II. Overview of ecological risk assessment

Despite numerous future promises, there is a multitude of concerns about the impact of GM crops on the environment. Key issues in the environmental assessment of GM crops are putative invasiveness, vertical or horizontal gene flow, other ecological impacts, effects on biodiversity and the impact of presence of GM material in other products. These are all highly interdisciplinary and complex issues. A crucial component for a proper assessment is defining the appropriate baseline for comparison and decision. For GM crops, the best and most appropriately defined reference point is the impact of plants developed by traditional breeding. The latter is an integral and accepted part of agriculture. In many instances, the putative impacts identified for GM crops are very similar to the impacts of new cultivars derived from traditional breeding. When assessing GM crops relative to existing cultivars, the increased knowledge base underpinning the development of GM crops will provide greater confidence in the assurances plant science can give on the risks of releasing such crops.

Assessment of the food safety issues related to genetically modified foods

International consensus has been reached on the principles regarding evaluation of the food safety of genetically modified plants. The concept of substantial equivalence has been developed as part of a safety evaluation framework, based on the idea that existing foods can serve as a basis for comparing the properties of genetically modified foods with the appropriate counterpart. Application of the concept is not a safety assessment per se, but helps to identify similarities and differences between the existing food and the new product, which are then subject to further toxicological investigation. Substantial equivalence is a starting point in the safety evaluation, rather than an endpoint of the assessment. Consensus on practical application of the principle should be further elaborated. Experiences with the safety testing of newly inserted proteins and of whole genetically modified foods are reviewed, and limitations of current test methodologies are discussed. The development and validation of new profiling methods such as DNA microarray technology, proteomics, and metabolomics for the identification and characterization of unintended effects, which may occur as a result of the genetic modification, is recommended. The assessment of the allergenicity of newly inserted proteins and of marker genes is discussed. An issue that will gain importance in the near future is that of post-marketing surveillance of the foods derived from genetically modified crops. It is concluded, among others that, that application of the principle of substantial equivalence has proven adequate, and that no alternative adequate safety assessment strategies are available.

Transformation of Acinetobacter sp. strain BD413(pFG4DeltanptII) with transgenic plant DNA in soil microcosms and effects of kanamycin on selection of transformants

Here we show that horizontal transfer of DNA, extracted from transgenic sugar beets, to bacteria, based on homologous recombination, can occur in soil. Restoration of a 317-bp-deleted nptII gene in Acinetobacter sp. strain BD413(pFG4) cells incubated in sterile soil microcosms was detected after addition of nutrients and transgenic plant DNA encoding a functional nptII gene conferring bacterial kanamycin resistance. Selective effects of the addition of kanamycin on the population dynamics of Acinetobacter sp. cells in soil were found, and high concentrations of kanamycin reduced the CFU of Acinetobacter sp. cells from 10(9) CFU/g of soil to below detection. In contrast to a chromosomal nptII-encoded kanamycin resistance, the pFG4-generated resistance was found to be unstable over a 31-day incubation period in vitro.