Impact of transgenic potatoes expressing anti-bacterial agents on bacterial endophytes is comparable with the effects of plant genotype, soil type and pathogen infection

1. Blackleg and soft rot disease of potatoes Solanum tuberosum L., mainly caused by the bacterial pathogen Erwinia carotovora ssp. atrospetica (Eca), lead to enormous yield losses world-wide. Genetically modified (GM) potatoes producing anti-bacterial agents, such as cecropin/attacin and T4 lysozyme, may offer effective future pathogen control strategies. Because of concerns about undesirable ecological side-effects of GM crops, it is important to analyse the potential environmental impact of GM crops carefully. The objective of this study was to investigate the effect of GM potatoes with anti-bacterial activity on the diversity and functional abilities of bacteria colonizing the intercellular spaces and vascular tissues (endosphere) of potato plants. 2. A greenhouse experiment was performed to analyse the effect of GM potatoes expressing either attacin/cecropin or T4 lysozyme on endophytic bacterial communities. Endophytic bacteria colonizing the GM potato lines as well as their nearly isogenic wild types were analysed at two vegetation stages. In order to compare GM-related variations with impacts caused by changing environmental conditions, potatoes were cultivated in two different soil types, and challenged with the pathogen Eca. Endophytic diversity was assessed by 16S rRNA-based terminal-restriction fragment length polymorphism (T-RFLP) analysis. Cultivated community members were identified by 16S rRNA gene analysis and screened for a range of plant growth-promoting and plant pathogen-antagonistic abilities. 3. Both genetic transformation events induced a differentiation in the community structures of associated bacterial populations and in the related functional abilities of cultivated bacterial endophytes. In comparison with the other factors analysed, the impact of both genetic modification types was minor or comparable with the variations caused by plant genotype, vegetation stage, pathogen exposure and soil type. 4. Synthesis and applications. This study has shown that the expression of anti-bacterial proteins may affect bacterial endophytes; however, the impacts were no greater than those of other factors analysed. Future risk assessment studies of GM crops should consider different environmental factors. This study contributes to the ongoing risk assessment of GM crops and provides valuable baseline information for prospective GM crop assays