Bacterial community composition in the rhizosphere of a transgenic, herbicide-resistant maize ( Zea mays) and comparison to its non-transgenic cultivar Bosphore

Abstract

Bacterial communities in rhizospheres of transgenic maize ( Zea mays, with the pat-gene conferring resistance to the herbicide glufosinate; syn. L-phosphinothricin) were compared to its isogenic, non-transgenic cultivar. Total DNA was extracted from bacterial cell consortia collected from rhizospheres of plants grown in an agricultural field. With the use of three different primer pairs binding to evolutionarily conserved regions of the bacterial 16S rRNA gene, partial sequences were amplified by polymerase chain reaction (PCR). The PCR products were subjected to single-strand conformation polymorphism (SSCP) to generate genetic profiles which corresponded to the diversity of the amplified sequences. Genetic profiles of rhizospheres consisted of 40–60 distinguishable bands depending on the chosen primer pairs, and the variability between independent replicates was very low. Neither the genetic modification nor the use of the herbicide Liberty (syn. Basta; active ingredient: glufosinate) affected the SSCP profiles as investigated with digital image analysis. In contrast, PCR–SSCP profiles of bacterial communities from rhizospheres of sugar beet, grown in the same field as a control crop, were clearly different. A less pronounced but significant difference was also observed with rhizosphere samples from fine roots of maize plants collected 35 and 70 days after sowing. Sequencing of the dominant 30 products from one typical SSCP profile generated from transgenic maize rhizospheres indicated the presence of typical soil and rhizosphere bacteria: half of the bands could be attributed to Proteobacteria, mainly of the α- and β-subgroups. Other SSCP bands could be assigned to members of the following phylogenetic groups: Cytophaga– Flavobacterium– Bacteroides, Chlamydiales– Verrucomicrobium, Planctomyces, Holophaga and to Gram-positive bacteria with a high G+C DNA content.