The Environmental Impact of Genetically Modified Crop Plants on the Microbiology of the Rhizosphere

Author: Diana Joyce Walter

Walter, Diana Joyce, 2005 The Environmental Impact of Genetically Modified Crop Plants on the Microbiology of the Rhizosphere, Flinders University, School of Medicine

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The effect of genetically modified crop plants on the microbiology of the rhizosphere was investigated using the single-gene Bt cotton as a case study. The project compared the rhizosphere microbiota of four Ingard® 1cotton plant varieties that were closely matched with their non-GM parental strains. The plants were grown in three different Australian soils, ie, a vertisol from a cotton-growing region, and two soils, a fine sandy loam and a red sand from South Australia that had not been exposed to cotton. At the time of the commencement of the project, the only commercially available genetically modified plants were cotton and carnations. The cotton industry in Australia is worth $1.5b annually, and care of the soil and the dynamics of its living microbial consortia needs to be understood for optimum management to enable agricultural sustainability. The general outline of the thesis incorporated four main sections: 1. Experimental setup and analysis of the soils and plants to be used, quantification of the Cry1A(c) plant-produced Bt protein, and its persistence in the soil environment. 2. Measurement of the selected microbial populations of bacteria, fungi, AMfungi, protozoans and nematodes, by counting and estimation by dilution and most-probable number methods. 3. Assessment of selected metabolic pathways to determine the effects on the soil microbial community by chemical and other biochemical methods 4. An overall analysis between different group ratios of expression of each of the variables tested, and the summary of the risk analysis and conclusion. The outcome of this work was the acquisition of scientific data to produce an environmental impact report. The findings of this study showed that generally the microbial populations and the products of major metabolic pathways correlated more closely within the non-GM and GM plant rhizospheres of the paired trials than those of separate trials, indicating that soil and plant cultivar had a stronger environmental effect. The results obtained from the paired trials did not show that there were consistent effects on the rhizosphere soil microbiota that could be attributed to the presence of the Cry1A(c) Bt plant protein on the selected strains of cotton plants. The results from the tests of the paired trials correlate highly with previously published work that the risk factors of genetically modified cotton plants on the microbiology of the rhizosphere soil were found be negligible and not consistent across trials. 1 ® Monsanto Co. St Louis, MO.

Keywords: microbiota,gm,cotton,rhizosphere,soil,Bt
Subject: Biotechnology thesis

Thesis type: Doctor of Philosophy
Completed: 2005
School: School of Medicine
Supervisor: Dr Chris. Franco