Evaluation of the Galega-Rhizobium galegae system for the bioremediation of oil-contaminated soil

The bioremediation potential of a nitrogen-fixing leguminous plant, Galega orientalis, and its microsymbiont Rhizobium galegae was evaluated in BTX (b enzene, toluene, xylene)-contaminated soils in microcosm and mesocosm scale . To measure the intrinsic tolerance of the organisms to m-toluate, a model compound representing BTX, G. orientalis and R. galegae were cultivated un der increasing concentrations of m-toluate alone and in association with Ps eudomonas putida pWWO, a bacterial strain able to degrade toluene-derived c ompounds. The test plants and rhizobia remained viable in m-toluate concent rations as high as 3000 ppm. Plant growth was inhibited in concentrations h igher than 500 ppm, but restituted when plants were transferred into m-tolu ate-free medium. Nodulation was blocked under the influence of m-toluate, b ut was restored after the plants were transferred into the non-contaminated media. In the mesocosm assay the Galega plants showed good growth, nodulat ion and nitrogen fixation, and developed a strong rhizosphere in soils cont aminated with oil or spiked with 2000 ppm m-toluate. Thus, this legume syst em has good potential for use on oil-contaminated sites (C) 2000 Elsevier S cience Ltd. All rights reserved.