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Applied and Environmental Microbiology, November 2005, p. 6719-6729, Vol. 71, No. 11
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.11.6719-6729.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Impact of Bt Corn on Rhizospheric and Soil Eubacterial Communities and on Beneficial Mycorrhizal Symbiosis in Experimental Microcosms

M. Castaldini,1 A. Turrini,2 C. Sbrana,3 A. Benedetti,4 M. Marchionni,4 S. Mocali,4 A. Fabiani,1 S. Landi,1 F. Santomassimo,1 B. Pietrangeli,5 M. P. Nuti,2,3 N. Miclaus,1 and M. Giovannetti2,3*

Istituto Sperimentale per lo Studio e la Difesa del Suolo, C. R. A., Piazza Massimo D'Azeglio 30, 50121 Florence, Italy,1 Dipartimento di Biologia della Piante Agrarie, Via del Borghetto 80, 56124 Pisa, Italy,2 Istituto di Biologia e Biotecnologia Agraria C. N. R., Sezione di Pisa, Via del Borghetto 80, 56124 Pisa, Italy,3 Istituto per la Nutrizione delle Piante, C. R. A., Via della Navicella 2/4, 00184 Rome, Italy,4 Istituto Superiore per la Prevenzione e la Sicurezza del lavoro, Via Urbana 167, 00184 Rome, Italy5

Received 14 April 2005/ Accepted 27 June 2005

A polyphasic approach has been developed to gain knowledge of suitable key indicators for the evaluation of environmental impact of genetically modified Bt 11 and Bt 176 corn lines on soil ecosystems. We assessed the effects of Bt corn (which constitutively expresses the insecticidal toxin from Bacillus thuringiensis, encoded by the truncated Cry1Ab gene) and non-Bt corn plants and their residues on rhizospheric and bulk soil eubacterial communities by means of denaturing gradient gel electrophoresis analyses of 16S rRNA genes, on the nontarget mycorrhizal symbiont Glomus mosseae, and on soil respiration. Microcosm experiments showed differences in rhizospheric eubacterial communities associated with the three corn lines and a significantly lower level of mycorrhizal colonization in Bt 176 corn roots. In greenhouse experiments, differences between Bt and non-Bt corn plants were detected in rhizospheric eubacterial communities (both total and active), in culturable rhizospheric heterotrophic bacteria, and in mycorrhizal colonization. Plant residues of transgenic plants, plowed under at harvest and kept mixed with soil for up to 4 months, affected soil respiration, bacterial communities, and mycorrhizal establishment by indigenous endophytes. The multimodal approach utilized in our work may be applied in long-term field studies aimed at monitoring the real hazard of genetically modified crops and their residues on nontarget soil microbial communities.

* Corresponding author. Mailing address: Dipartimento di Biologia della Piante Agrarie, Università di Pisa, Via del Borghetto 80, 56124 Pisa, Italy. Phone: 39 050 9719324. Fax: 39 050 571562. E-mail: mgiova{at}agr.unipi.it.

Applied and Environmental Microbiology, November 2005, p. 6719-6729, Vol. 71, No. 11
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.11.6719-6729.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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