In recent years substantial research has been applied to biodegradation. This has resulted in improved knowledge of key issues ranging from the biochemistry and genetics of degradation pathways to bacterial ecology, physiology, inoculation techniques and contaminant bioavailabilty. However, little of this knowledge has been put into practice so far. Bioremediation bacteria have been engineered, but mostly for the degradation of model compounds with little industrial relevance. In addition, industrial exploitation of these strains was prevented due to poor inoculant survival, low bioavailability of contaminants and the economic cost of soil/incocula mixing.
This project will address a number of these difficulties, and seek to overcome the problems associated with previous bioremediation practices, through the exploitation of integrated plant/microbe systems for contained degradation.
The proposed project will exploit the experiences of recent and current research, including EU-funded R&D work, to deliver innovative plant/microbe systems for effective soil bioremediation. The systems will utilize existing rhizosphere-competent bacterial isolates for the colonization of selected plant species. These bacterial strains will be genetically modified to highly express various degradation genes in response to signals from root exudates. This will be achieved by fusing existing plant exudate-responsive bacterial promoters to promoter-less degradation gene cassettes. In addition, the same promoters will be used for the development of rhizosphere-specific containment systems, whereby inoculant survival will be dependent on the presence of the host plant.
The proposed in situ technology will make use of crop plants (Beta vulgaris, Medicago sativa) or trees (Salix spp.), combined with these novel GEMs. Plant seeds or cuttings will be inoculated with the GEMs, employing standard incoculation techniques, and planted in contaminated soil. The growing plant roots, being colonized by the GEMs, will act as an inexpensive yet efficient vehicle for distributing the degrading bacteria in the soil volume, thus avoiding the requirement for mechanical distribution. In addition, the plant roots will, through their water consumption, cause massflow of contaminants to the bacteria. In essence the integrated system will behave as an " in situ degradation bioreactor".
The genetic modifications will exploit well described genetic regulatory systems from several microbial genera that are available within the partnership. These include bph, nah and tom gene cassettes, plant regulated bacterial promoters and existing engineered strains that are available for field testing. Several independent plant/GEM models will be evaluated, using microbial constructs with interchangable degradation genes, so that the system can be applied to a number of different soil contaminants, including PCBs, PAHs and TCE, in this project. The best-performing system(s) will be field-evaluated.
The project partnership includes leading European and American laboratories experienced in the disciplines of biodegradation genetics, bacterial rhizosphere ecology, molecular ecology and soil microbial ecology. In addition, several partners are well-acquainted with the European administrative mechanisms of deliberately releasing GEMs, and with strain testing procedures required prior to receiving such permits. The level of industrial interest in this proposal is reflected by the involvement of a number of industrial partners from the bioremediation sector and seed industry. During the course of the project the industrial partners will act as advisors for the research and development effort, to focus the project towards field application, and as a liaison with endusers.
Funding SchemeCSC - Cost-sharing contracts