Tuesday, November 14, 2006

Microbial Populations and Enzyme Activities in Soil in situ under Transgenic Corn Expressing Cry Proteins from Bacillus thuringiensis.

Isik Icoz1, Deepak Saxena1, David Andow2, Claudia Zwahlen2, and Guenther Stotzky1. (1) NYU, Dept of Biology, Laboratory of Microbial Ecology, New York, NY 10003, (2) Univ of Minnesota, Dept of Entomology, St. Paul, MN 55108

Transgenic Bt crops produce insecticidal Cry proteins that are released into soil via root exudates and plants residues and may affect soil microorganisms. As a continuation of studies in the laboratory and plant-growth room, a field study is being conducted at the Rosemount Experiment Station of the University of Minnesota. Four Bt corn varieties [(Novartis N45-A6, Novartis Attribute GSS-0966, and Pioneer 38A25 that express Cry1Ab protein, which is toxic to the European corn borer (Ostrinia nubilalis), and DeKalb DKC46-24 that expresses Cry3Bb1 protein, which is toxic to the corn rootworm complex (Diabrotica sp.)] and their near-isogenic non-Bt varieties (N45-T6, PrimePlus, 38A24, and DKC46-28, respectively) are being evaluated for their effects on microbial diversity and enzyme activities in soil. Soils collected in August 2003, August 2004, three times in 2005 (before planting, midseason, and after harvest), and April 2006 were analyzed by classical dilution plating and molecular biology (PCR/DGGE) techniques. In general, there were no consistent statistically significant differences in the numbers of different groups of microorganisms, the activities of some enzymes involved in the degradation of plant biomass, and pH between soils planted with Bt and non-Bt corn. The numbers and types of microorganisms and enzyme activities differed with season, but these differences were not related to the presence of the Cry proteins in soil. Cry1Ab protein was detected in most soils during the three years, whereas Cry3Bb1 protein was not detected in rhizosphere or bulk soil of Bt corn expressing cry3Bb1. Cry3Bb1 protein was detected in root exudates of Bt corn in sterile hydroponic culture and in nonsterile rhizosphere soil in the laboratory only at very low levels in contrast to Cry1Ab protein, which was detected at higher levels, suggesting that Cry3Bb1 protein does not persist as long as Cry1Ab protein in soil.

Handout (.ppt format, 6618.0 kb)