The report consists of a generic part (A) and a special part (B). Part (A) of this literature study gives an overview of the ecological significance of micoorganisms in general. A further focus is the discussion of existing attempts at assessing and evaluating ecological risks which may occur following the release of bacteria with certain properties, e.g. genetically modified bacteria (GMOs). As a possible alternative approach a quantitative evaluation strategy, which is oriented in analogy to the PEC/PNEC-approach for chemicals or pesticides was worked up. The evaluation strategy is characterized mostly that the fate of microorganisms or genes as well as their effect on ecosystem structures and processes for different environmental compartments is quantitied separately. The assessment of the risk for the environment occurs then on the basis of compartment specific dose-effect relationships. Special emphasis was placed here also on the possibilities for standardizable experimental determination of effects (effects on the environment). For this also the existing test guidelines for the ecotoxicological testing of chemicals and pesticides as well as microbial pesticides with respect to their applicability of the testing of GMOs was evaluated. Part (B) of the literature study is a compendium about the ecology of six bacteria species whose release in the context of agricultural or biotechnical application has already occurred or is expected from the stand of research: Bacillus thuringiensis, B. subtilis, Pseudomonas fluorescens, P. putida, Rhizobium leguminosarum and Sinorhizobium meliloti. The information concerning the ecology of these organisms applies to specific living spaces as well as the distribution of the bacteria, their influence on the nutrient status in nature and their role within the biotic system. (orig.)Available from TIB Hannover: RN 8422(1998,64) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Umwelt, Naturschutz und Reaktorsicherheit, Bonn (Germany)DEGerman