Environmental impact of genetically modified Rhizobium leguminosarum bv viciae

Experiments aimed at assessing the effects following the field release of genetically modified microorganisms (GMO) were carried out. Derivatives of different strains of Rhizobium leguminosarum bv. viciae were constructed carrying environmentally-neutral reporter genes or resistance determinants to non-antibiotic compounds, and released in soil in the presence of pea host plants. Genes were chosen that would not confer selective advantage to the GMOs in the environment of choice, in order to evaluate any net impact of a genetic modification per se. Two strains were used as background and tagged with the same modifications, the first was isolated from a location distant from the site of the release, the second represented the dominant pea-nodulating strain within the indigenous populations of the site. These differences of origin played a major role in the ecological outcome of the symbiosis, in that the foreign strain, behaved extremely poorly, both in persistance and in infection, being severely outcompeted by the natural rhizobia, while the autochtonous derivative maintained the competitive dominant attitude of its parental version, occupying the majority of the host nodules. However, monitoring the effects of both releases by viable plate counts of different microbial groups including aerobic bacteria, fungi, actynomycetes, fluorescent pseudomonads, other rhizobia and some representative soil activities, did not reveal any perturbations, confirming that a genetic modification per se, does not inherently produce an impact even when carried by a species that succesfully and extensively colonizes its habitat