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United States Department of Agriculture

Agricultural Research Service

Title: Bacterial Communities of the Rhizosphere and Endorhiza Associated with Field-Grown Cucumber Plants Inoculated with a Plant Growth-Promoting Rhizobacterium Or Its Genetically Modified Derivative

Authors
item Mahaffee, Walter
item Kloepper, J - AUBURN UNIVERSITY

Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 1996
Publication Date: N/A

Interpretive Summary: The manuscript describes experiments on the impact of genetically modified bacterium on the bacterial communities of two habitats (rhizosphere [root surface and adhering soil] and endorhiza [internal tissues of the root]) associated with plant tissues. This work confirmed previous reports from greenhouse, microcosom, and gnotobiotic systems that genetic modification of a bacterial strain does not cause a difference in its environmental impact. A two-year field study was established to examine whether the indigenous bacterial communities of the rhizosphere and endorhiza (internal root tissues) were affected differently by the introduction of an unaltered wild-type and its genetically modified derivative. Treatments consisted of the wild-type PGPR strain Pseudomonas fluorescens 89B-27, and a bioluminescent derivative GEM-8 (89B-27::Tn4431). Cucumber root or seed samples were taken and processed to examine the bacterial communities of both the rhizosphere and endorhiza. Over 7,200 bacterial colonies were isolated from the rhizosphere and endorhiza and identified to genus using the Sherlock System (Microbial ID, Inc.) for fatty acid methyl ester analysis. Community structure at the genus level was assessed using genera richness, and Hill's diversity numbers, N1 and N2. The data indicate that the introduction of the genetically modified derivative of 89B-27 did not pose a greater environmental risk than its unaltered wild-type with respect to aerobic-heterotroph bacterial community structure.

Technical Abstract: The future use of genetically modified microorganisms in the environment will be dependent on the ability to assess potential or theoretical risks associated with their introduction into natural ecosystems. To assess potential risks, several ecological parameters must be examined, including the impact of the introduced genetically modified organism on the microbial communities associated with the environment into which the introduction will occur. A two-year field study was established to examine whether the indigenous bacterial communities of the rhizosphere and endorhiza (internal root tissues) were affected differently by the introduction of an unaltered wild-type and its genetically modified derivative. Treatments consisted of the wild-type PGPR strain Pseudomonas fluorescens 89B-27, and a bioluminescent derivative GEM-8 (89B-27::Tn4431). Cucumber root or seed samples were processed to examine the bacterial communities of both the rhizosphere and endorhiza. Over 7,200 bacterial colonies were isolated from the rhizosphere and endorhiza and identified using the Sherlock System (Microbial ID, Inc.) for fatty acid methyl ester analysis. Community structure at the genus level was assessed using genera richness, and Hill's diversity numbers, N1 and N2. The aerobic-heterotroph bacterial community structure at the genus level did not significantly vary between treatments but did differ temporally. The data indicate that the introduction of the genetically modified derivative of 89B-27 did not pose a greater environmental risk than its unaltered wild-type with respect to aerobic-heterotroph bacterial community structure.

Last Modified: 10/21/2014
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