The objectives in this research were to assess whether Klebsiella planticola SDF20 could survive in soil and result in ecological effects to soil foodweb organisms and plant growth. Four experiments were conducted using soil microcosms. Klebsiella planticola SDF20 has been genetically engineered to produce ethanol from agricultural waste for use in alternative fuels. Theoretically, after ethanol is removed from fermentors, the remaining residue that includes SDF20 would be spread onto crop fields as organic amendments. The parent strain SDF15 and genetically engineered strain SDF20 were added to sandy and clay soils with varying organic matter content. Alterations to soil foodweb organisms and plant growth were assessed using direct methods. These alterations were considered to be ecological effects if changes in nutrient cycling processes and plant growth would result. Ethanol produced by SDF20 was detected in the headspace of microcosms that demonstrated that SDF20 can survive and express its novel function in high organic matter clay soil. Soil containing higher organic matter and higher clay content may have increased the survival of SDF20 due to less competition with indigenous microbiota for substrates and protection from bacterial predators in clay soil with smaller pore sizes, thereby allowing SDF20 to produce a detectable concentration of ethanol. Significant changes to soil foodweb organisms were not detected using this soil type. However, significant increases in soil nematodes and significant decreases in vescular-arbuscular mycorrhizal colonization of plant roots were detected after the addition of SDF20 to low organic matter clay, low organic matter sandy and high organic matter sandy soils. Significant changes in soil foodweb organisms associated with SDF20 occurred only when living plant roots were present. This indicated the importance of having biotic interactions in test systems to elucidate ecological effects. The effects associated with SDF20 varied with the chemical, physical and biological properties of soils and indicated the importance of assessing the release of genetically engineered microorganisms on a case by case basis. / Graduation date: 1996