Transgenic maize expressing Bacillus thuringiensis (Bt) insecticidal crystal (Cry) proteins may contribute to a decreased need for chemical pesticides, providing benefits for human health and the environment. However, there is public concern regarding the environmental safety of transgenic crops, which relates also to potential adverse effects on plant-microbe interactions by affecting the plant-associated, endophytic microflora. Thus, we compared the endophytic bacterial communities in plants of the three transgenic Bt maize lines MON89034 (cry3Bb1), MON88017 (cry1A.105 and cry2Ab2) and the stacked event MON88017xMON89034 (cry1A.105 and cry2Ab2, cry3Bb1), with those of the respective near-isogenic line, and with those in plants of three additional, conventional maize lines. The maize plants were grown in a containment system on two different soils which were commonly used for maize cultivation in Lower Austria.

We obtained 700 bacterial endophytes and characterized them regarding their phylogenetic diversity and specific plant growth promoting functions, including the production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and indole-3-acetic acid (IAA). Both the soil environment and the plant cultivar had an effect on the phylogenetic diversity of the endophytic communities, but there were no specific effects of the transgenic varieties. Diversity measures of endophytic isolates were not different in Bt- versus non-Bt maize varieties. A variable number of isolates showed ACC deaminase activity irrespective of the soil and plant cultivar. Generally, the number of high IAA producers appeared to be affected by the soil environment but not by the plant cultivar. Cultivation-independent profiling via terminal restriction fragment polymorphism (T-RFLP) analysis of the 16S rRNA gene revealed that maize root endophytes were differentially composed dependent on soil type and plant cultivar, but they were not discriminated with respect to Bt- versus non-Bt varieties. In conclusion, maize endophyte communities studied were highly diverse and showed a high potential for plant growth promotion, emphasizing their importance in modern agricultural systems irrespective of the maize cultivar, including Bt-modifications.