Serine protease inhibitors (PIs) are involved in several physiological processes, such as regulation of endogenous proteinases and defence against phytophageous insects. Transgenic modifications have enhanced protease inhibitor expression to develop insect resistant cultivars in several important crops. The fate of protease inhibitors released from genetically engineered plants is an important issue because of possible inhibition of soil proteases and effects of the insecticidal protein and its codifying sequence on soil microorganisms. The persistence of transgenic sequence mustard trypsin inhibitor-2 in soil and its hypothetical acquisition by soil microorganisms by horizontal gene transfer and the effect of transgenic plant material on soil microbial community structure and soil protease activity were investigated. With the aim to simulate the effects of plant litter on soil microorganisms, a microcosm experimental model was used. Despite the persistence of transgenic DNA sequences, no recombination event was detected between plant DNA and soil bacteria; molecular analysis of bacterial community also showed no significant influence on the dominant members of the bacterial community and soil protease activity was not inhibited by the release of constitutively over-expressed protease inhibitor.

