Release of the recombinant Cry3Bb1 protein of Bt maize MON88017 into field soil and detection of effects on the diversity of rhizosphere bacteria

A three-year experimental field study with a genetically engineered Bt maize (event MON88017) and three conventionally bred cultivars was conducted to quantify the recombinant Cry3Bb1 protein released into soil and detect effects on the diversity of soil bacteria. Protein extraction and an enzyme-linked immunosorbent assay (ELISA) allowed a threshold detection of 0.01 ng Cry3Bb1 g−1 soil. The maximum amount found in field plots with Bt maize was 1.0 ng Cry3Bb1 g−1 rhizosphere soil. Average concentrations during the growing seasons varied between years from 0.07 to 0.29 ng g−1. No accumulation of Cry3Bb1 in soil occurred over the three growing seasons. Four weeks after harvest, the major Cry3Bb1 reservoirs on the field were the remaining root stubbles, but their Cry3Bb1 concentration declined by 98.30–99.99% in the following seven months. During the three consecutive years of study there were never significant differences between the rhizosphere bacterial community structure of the Bt maize and the other cultivars, as detected by cultivation independent profiling of PCR-amplified 16S rRNA genes. The low concentrations of soil extractable Cry3Bb1, its degradation in decaying roots, and the lack of effects on rhizosphere bacteria give no indications of adverse effects of MON88017 cultivation on soil ecology.