Survival and ecological effects of genetically engineered Erwinia carotovora in soil and aquatic microcosms

Abstract

The release of genetically engineered organisms into the environment has raised concerns about their potential ecological impact. In this study, genetically engineered Erwinia carotovora strains expressing varying levels of reduced phytopathogenicity and wildtype E. carotovora strains were used in aquatic and soil microcosms to assess the survival, intraspecific competition, and effects upon specific groups of indigenous bacteria. In aquatic microcosms, the densities of Erwinia genetically engineered organisms (GEMs) and wildtype strains declined and fell below the detectable limit of plate counts 15 d after the microcosms were inoculated. In aquatic microcosms, engineered E. carotovora did not exhibit a competitive advantage over the wildtype. The effect of engineered and wildtype E. carotovora on densities of total and selected bacteria was not significantly different. Treatment with engineered E. carotovora did not change biomass values of the receiving community but did cause a transitory increase in metabolic activity. In aquatic microcosms, the inability of genetically engineered E. carotovora to persist, displace resident species, or affect the metabolic activity of aquatic communities indicates the low risk of adverse ecological consequences in aquatic ecosystems. Unlike previous investigations involving soil microcosms, densities of both the genetically engineered and wildtype E. carotovora remained at detectable levels over 60 d in both agricultural clay and forest loam soils. The type of soil significantly affected the survival of the GEM and the wildtype. The sorptive properties of clay particles, as well as low concentrations of soil nutrients and organic matter, may have contributed to the unexpected patterns of GEM and wildtype survival.