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Title: SOIL MICROBIAL COMMUNITIES GROWN WITH BT AND NON-BT CORN IN THREE SOILS

Author
item Blackwood, Christopher
item Buyer, Jeffrey

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2003
Publication Date: 5/1/2004
Citation: Blackwood, C.B., Buyer, J.S. 2004. Soil microbial communities grown with Bt and non-Bt corn in three soils. Journal of Environmental Quality. 33:832-836.

Interpretive Summary: Transgenic Bt corn has been genetically modified to express an insecticidal protein, Cry endotoxin, originally found in the bacterium Bacillus thuringiensis, in order to control certain insect pests. In order to determine whether the expression of Cry endotoxin by corn has any effects on soil microorganisms, we grew two lines of Bt corn expressing different Cry endotoxins, and their respective non-Bt isolines, in a growth chamber experiment. We used three soil types of differing textures (i.e. relative amounts of sand, silt, and clay). The makeup of the soil microbial community was determined by analysis of phospholipid fatty acids extracted directly from soils. Soil type had a major impact on the phospholipid fatty acid profiles, but the overall patterns were not affected by expression of the Cry endotoxins or corn line. There was a significant reduction in a biomarker specific for eukaryotes due to expression of Cry endotoxin, although it is unclear which groups of eukaryotes were affected. Communities of bacteria and fungi living in proximity to the corn roots were also characterized by their patterns of growth on 95 carbon sources, called community-level physiological profiles. Soil type had a statistically significant, but overall quite small effect on physiological profiles. In the high clay soil only, both expression of Cry endotoxin and corn line had statistically significant but small effects on physiological profiles (accounting for 6.6 and 6.1% of the variability in that soil, respectively). It is concluded that the effects of transgenic Bt corn in this short-term experiment are small, and longer-term investigations are necessary.

Technical Abstract: The effects of expression of Cry endotoxin by transgenic Bacillus thuringiensis (Bt) corn on soil microbial community structure were assessed in a growth chamber experiment. Two lines of transgenic corn expressing different Cry endotoxins were compared to their respective non-transgenic isolines in three soil types with differing textures. Phospholipid fatty acid (PLFA) profiles from bulk soil and community level physiological profiles (CLPP) from the rhizosphere community were used to assess community structure. Differences in PLFA profiles due to soil type were significant, accounting for 73% of the total variability in the dataset. Differences in bacterial and fungal CLPP profiles due to soil type were statistically significant, but probably not biologically important, accounting for 6.3 and 3.8% of the total variability, respectively. Neither expression of Cry endotoxin nor corn line had a significant effect on microbial profiles, except in the high-clay soil where both factors significantly affected bacterial CLPP profiles (accounting for 6.6 and 6.1% of the variability in that soil, respectively). Expression of Cry endotoxin also significantly reduced the presence of eukaryotic PLFA biomarker in bulk soils, although it is unclear which groups of eukaryotes were affected. It is concluded that the effects of transgenic Bt corn in this short-term experiment are small, and longer-term investigations are necessary.