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Unintended Effects of Genetic Manipulation
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Bt maize had changed lipid composition in stems; also, lipid composition in soil was altered, and soil respiration was reduced.

Manipulated Organism: Maize (Zea mays).

Inserted Transgenes: crylAb gene from Bacillus thuringiensis (Bt). This gene gives transgenic Bt maize (also called Bt corn) the ability to produce insecticidal delta-endotoxin that can kill the larvae of the European corn borer and other insect pests feeding on the corn. The gene was fused to the cauliflower mosaic virus (CaMV-35S) promoter so that the Bt gene would be expressed in all parts of the plant.

Goal of This Study: Examine whether Bt maize differs from its nontransgenic conventional counterpart in respect to (1) extractable lipids in the plant stems, (2) extractable lipids in the soil in which the plants had been cultivated, and (3) soil respiration in soils in which the plants had been cultivated and which also contained plant residues. Soil respiration is an indicator of the intensity of the breakdown of organic matter, mainly through microbial soil organisms. The researchers used a commercial variety of Bt maize (Pioneer 38W36) and compared it to its non-genetically modified conventional counterpart (Pioneer 3893).

Results of This Study: The researchers found:
  • Significant differences in the concentrations of different extractable lipids in the stems (shoots) of Bt and conventional maize. "Bt shoots were significantly lower in alkenes but richer in n-alkanes, n-fatty and unsaturated fatty acids than non-Bt shoots" (p. 217). Some of the specific differences included:
    • Concentrations of total alkenes (unsaturated hydrocarbons) in conventional maize stems was 47.9% higher than in Bt maize stems.
    • One alkene type was missing altogether in Bt stems. A different alkene made up half of the total alkene content in Bt maize and only 13% in conventional maize.
    • In Bt maize there was also a shift in concentrations of the different n-alkanes (saturated hydrocarbons); for example, one type made up 25% of the n-alkanes in Bt maize stems while the same n-alkane made up only 3% of total n-alkanes in conventional maize stems.
  • Significant differences in the concentrations of different extractable lipids in soils in which Bt maize and conventional maize had been grown. "Bt soils were lower in alkenes and unsaturated fatty acids but richer in n-alkanes and n-fatty acids than non-Bt soils" (p. 217). Some of the specific differences included:
    • Total alkane concentrations were 21.3% higher in soils in which conventional maize grew.
    • "One striking feature was the dominance of unsaturated fatty acids in non-Bt soils.... [while in] Bt soils n-fatty acid concentrations were twice as high as those in non-Bt soils" (p.216 and p. 217).
  • Significant differences in soil respiration. Respiration decreased by 30.5% under Bt crops. This "soil respiration study strongly suggests that the chemical nature of the Bt maize shoots and their biological reactivity, as indicated by the extractable lipids, are changed following gene modifications.... Cultivation of Bt maize appears to significantly increase the saturated to unsaturated lipid relation in soils and so affect soil microbial activity. Loss of unsaturated lipids from Bt soils may lower the chemical reactivities of these soils" (p. 218).
The authors conclude: "The concerns raised by our data are serious enough to emphasize the need to further research the impact of Bt maize on short- and long-term soil quality" (p. 218).

Source: Dinel, H., M. Schnitzer, M. Saharinen, F. Meloche et al. (2003). "Extractable Soil Lipids and Microbial Activity as Affected by Bt and Non Bt Maize Grown on a Silty Clay Loam Soil," Journal of Environmental Science and Health Part B vol. B38 pp. 211-19.

Author Affiliations: Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada; University of Potenza, Italy.

Funding: Not mentioned.

Product Status: Bt maize has been commercially grown since the late 1990s.

Copyright 2008 The Nature Institute.

This document: http://natureinstitute.org/nontarget/reports/maize_006.php

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