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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #176539
Title: BACTERIAL DIVERSITY OF RHIZOSPHERES OF NON-TRANSGENIC AND TRANSGENIC CORN

Author
item FANG, MIN - UMC
item Kremer, Robert
item MOTAVALLI, PETER - UMC
item DAVIS, GEORGIA - UMC

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2005
Publication Date: 7/1/2005
Citation: Fang, M., Kremer, R.J., Motavalli, P.P., Davis, G. 2005. Bacterial diversity of rhizospheres of non-transgenic and transgenic corn. Applied and Environmental Microbiology. 71(7):4132-4136.

Interpretive Summary: Corn genetically modified (GM) for resistance to insect pests (Bt) or for resistance to the herbicide Roundup (Roundup Ready) is planted on about 30% of the corn production area of the United States. Although GM corn has received attention regarding human health concerns, its impact on the soil environment and soil ecology has been studied only to a limited extent. Effects on resident soil organisms responsible for important biological processes in the corn root zone (rhizosphere) have been largely neglected in environmental assessments of GM corn. Our objective was to determine the impacts of growing GM corn on the biodiversity of the complex bacterial populations that typically reside in the corn rhizosphere. In our study, biodiversity is an expression of the variety of viable bacteria in the rhizosphere based on the number and types of substrates (food sources) used and on the number of different bacterial groups detected by genetic analysis (DNA profiles). We found that the two GM corn varieties did not affect bacterial biodiversity, measured either by substrate use or DNA profiling, when compared to identical but non-GM corn varieties. Bacterial diversity changed slightly during the corn growing season, which is expected because corn roots release different substrates into soil as the plant develops. The greatest effect on changes in bacterial diversity was due to differences in soil texture, regardless of corn variety growing in the soil. Bacterial diversity was lowest in the coarse-textured sandy loam and highest in the finer-textured silt loam. The overall results indicate that when grown on the same soil, GM corn likely does not alter bacterial diversity in the rhizosphere relative to growth of non-GM corn. Because we only investigated two GM corn varieties, follow-up research is required to verify that these results are representative of the hundreds of GM varieties currently available for production in different soils and environments. Also, our results suggest only that the composition of the bacterial community was not affected; we did not study effects on specific biological processes mediated by rhizosphere bacteria, which should be pursued in the future. Nevertheless, the current information has important implications for scientists, extension personnel, producers, and environmental stakeholders because it demonstrates that growth of GM corn (Bt and Roundup Ready) has little effect on bacteria associated with roots and, thus does not disrupt this aspect of the soil environment.

Technical Abstract: Bacterial diversity was determined in transgenic and non-transgenic corn rhizospheres for three soils. In greenhouse and field studies, metabolic profiling and molecular analysis of 16S rRNAs differentiated bacterial communities among soil textures but not between corn varieties. We conclude that bacteria in corn rhizospheres are affected more by soil texture than by cultivation of transgenic varieties