Monitoring Genetically Manipulated Microorganisms in the Environment Clive Edwards, Department of Genetics and Microbiology, University of Liverpool, UK Genetically-manipulated microorganisms (GEMs) have been proposed for a variety of applications that would involve their release into open environments that already harbour a diverse and often highly active microflora. This proposal is controversial, especially in view of the problems in studying the fate and survival of GEMs in natural ecosystems. This book describes methods for the detection of target organisms in heterogeneous populations. The tendency of some species to adopt viable but non-culturable states is addressed. Molecular genetic methods that have the potential to overcome this problem are presented. These are also illustrated by their application as detection methods in aquatic environments. Terrestrial habitats are discussed using a description of a contained microcosm for release and recovery of genetically modified Gram-positive bacteria. Detailed methods for the quantitative extraction of microorganisms from soil are reviewed, along with an overview of experimental systems that have attempted to define the fate of GEMs in soil as well as to assess gene transfer events. The final chapter deals with models that describe microbial interactions in the environment. Although the chapters in this book are principally aimed at those working with genetically manipulated microorganisms there is no doubt that much of what is discussed is equally applicable to increasing our understanding of microbial ecology in general.