Transgenic Bt crops produce insecticidal Cry proteins that are
released to soil in plant residues, root exudates, and pollen and that may
affect soil microorganisms.
As a continuation of studies in the lab. and a plant-growth room, a
field study was conducted at the Rosemount Expt. Station of the University
of Minnesota.

Three Bt corn varieties that express the Cry1Ab protein, which is
toxic to the European corn borer (Ostrinia nubilalis Hubner), and one Btcorn
variety that expresses the Cry3Bb1 protein, which is toxic to the corn
rootworm complex (Diabrotica spp.), and their near-isogenic non-Bt varieties
were evaluated for their effects on microbial diversity by classical diln.
plating and mol. (polymerase chain reaction-denaturing gradient gel
electrophoresis) techniques and for the activities of some enzymes
(arylsulfatases, acid and alk. phosphatases, dehydrogenases, and proteases)
involved in the degrdn. of plant biomass.

After 4 consecutive years of corn cultivation (2003-2006), there were,
in general, no consistent statistically significant differences in the nos.
of different groups of microorganisms, the activities of the enzymes, and
the pH between soils planted with Bt and non-Bt corn. Nos. and types of
microorganisms and enzyme activities differed with season and with the
varieties of corn, but these differences were not related to the presence of
the Cry proteins in soil. The Cry1Ab protein of Bt corn (events Btl1 and
MON810) was detected in most soils during the 4 yr, whereas the Cry3Bb1
protein was not detected in soils of Bt corn (event MON863) expressing the
cry3Bb1 gene.

Reference
Icoz, I., Saxena, D., Andow, D. A., Zwahlen, C., Stotzky, G. (2008).
Microbial Populations and Enzyme Activities in Soil in Situ Under Transgenic
Corn Expressing Cry Proteins from Bacillus Thuringiensis. Journal of
Environmental Quality37(2): 647-662.
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