Ecological implications of the release of genetically engineered microorganisms (GEMs) into aquatic ecosystems

The recent development of recombinant DNA techniques enables the genetic engineer to manipulate genetic information to produce new microorganisms with novel phenotypes. The commercialization of this technology has led to the development of recombinant organisms specifically designed to be released into natural environments.; The fate of genetically engineered bacteria and their ability to cause perturbations on ecosystem structure and function is the focus of this study. Microcosm studies were designed to evaluate the fate of model engineered Pseudomonas putida strains in an oligotrophic freshwater system. By monitoring bacterial survival and plasmid stability, the effects of low-organic nutrient environments on the fate of an introduced organism and its foreign DNA were determined. Results of this study suggested that strain-specific postrelease adaptations tend to increase the fitness of GEMS for survival and establishment of populations in aquatic ecosystems. In addition, the effects of nutrient availability on horizontal gene transfer were also evaluated using laboratory donor strains and indigenous bacterial isolates. Results of this study suggested that rates of plasmid transfer in aquatic ecosystems may be higher in microenvironments of higher nutrient availability such as particle surfaces.; The final approach of this study was to determine the effects of a recombinant marine bacterium on phosphorus cycling in marine ecosystems. An indigenous marine bacterium, genetically modified to constitutively produce alkaline phosphatase, was released into seawater microcosms. By amending microcosms with various organophosphorus and nitrogen concentrations, the effect of the introduced GEM on the mineralization of dissolved organic phosphorus compounds was determined under both limiting and non-limiting inorganic nitrogen conditions. In addition the impact of the GEM on higher trophic levels, particularly the indigenous phytoplankton community, was determined. GEM- specific increases in the concentration of inorganic phosphate were observed during incubation in natural seawater. Secondary GEM-specific effects were observed in the phytoplankton community as determined by increases in chlorophyll a concentrations.