Intact soil-core microcosms for evaluating the fate and ecological impact of the release of genetically engineered microorganisms.

Intact soil-core microcosms were studied to determine their applicability for evaluating the transport, survival, and potential ecosystem effects of genetically engineered microorganisms before they are released into the environment. Soil-core microcosms were planted with wheat and maize seeds and inoculated with Azospirillum lipoferum SpBr17 and SpRG20a Tn5 mutants, respectively. Microcosm leachate, rhizosphere soil, plant endorhizosphere, insects, and xylem exudate were sampled for A. lipoferum Tn5 mutant populations. A. lipoferum Tn5 populations, determined by most-probable-number technique-DNA hybridization, varied from below detection to 10 g of dry root in the rhizosphere, with smaller populations detected in the endorhizosphere. Intact soil-core microcosms were found to maintain some of the complexities of the natural ecosystem and should be particularly useful for initial evaluations of the fate of plant-associated genetically engineered bacteria.