2004 IRISH SCIENTIST YEAR BOOK

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Institute of Technology Carlow
Institute of Technology Carlow
GM-Rhizoremediation – Developing sustainable biological solutions for the treatment of soil pollutants

(Figure 1) Schematic basis of biosensor for detecting bio-availability and degradation of PCBs. The bph operon encodes genes necessary for the metabolism of PCBs. The end products of this process are chlorobenzoates, which can act as inducers of the Pm-gfp reporter by way of the regulator XylS. The response can be observed at the single cell level by epi-fluorescent of CFSL microscopy.

The Institute of Technology Carlow is currently co-ordinating an EU Research and Technological Development project 'Testing Integrated GM-Rhizoremediation systems for soil bioremediation (GM-Rhizoremediation)' that involves eight partners from six countries (Table 1).


This interdisciplinary project intends to advance rhizoremediation – the combined application of plants and rootzone bacteria for soil cleaning – in two essential aspects. Firstly, bacteria engineered for in situ PCB (polychlorinated biphenyl) degradation will be further developed as biosensor strains, i.e., to signal the bio-availability of the pollutant in plant and soil, the efficacy of the bioremediation strains, the formation of the intermediate product chlorobenzoates (CBA), and determination of the end point of degradation.

In a second, complementary approach, molecular detection methods for tracking degrader bacteria in the environment will be developed to detect and quantify the GM strains under environmental conditions, and to monitor effects on microbial community structure in the polluted soil. Mathematical environmental modelling of the process and a detailed risk assessment is also under development.


Single cell biosensors

One of the most exciting aspects of the project is the development of integrated biosensor strains to facilitate in situ monitoring of PCB remediation (Figure 1). The system developed allows the detection of bio-available PCBs at levels as low as 100nM. In particular, these tools will allow efficacy monitoring of bioremediation inoculants in real situations. The findings will lead to a better understanding of those measures to be applied for optimisation of phytobioremediation technology.


Molecular detection systems

Novel molecular tools have been developed for the identification and unambiguous quantification of genetically modified (GM) bacterial strains in the environment. In addition, the impact of the inoculant on microbial community composition is being investigated by molecular approaches. Extensive testing of the system in willow plants (Figure 2) and other plant species is near completion. The role of plant in addition to bacterial enzymes is also being assessed. A detailed impact assessment on the use of the GM strains has been undertaken and modelled. We are currently preparing guidelines on the safe use, advantages and limitations of this bioremediation technology.


(Figure 2) Inoculation of Willow plants with degrader bacterial to test Rhizoremediation. Willow stems are first rooted in water and then inoculated with the PCB-degrader bacteria. Plants and bacteria are planted in soil contaminated with PCBs. The microcosm is evaluated over a five month period for various parameters including: degraders, microbial population make-up, plant health, and PCBs and their end-products.


Future directions

Although working with a model system, the project has generated results that are of general interest that can be applied to bioremediation and environmental protection. These include:

  • Characterised rhizosphere/soil strain(s) to degrade PCBs: principle can be extended to other target compounds

  • Inoculant technologies to introduce strains to the contaminated soil/ rhizosphere environment

  • Biosensor-functionality of strains for monitoring in situ activity: could be extended to other compounds e.g. MTB, TBT

  • High-level gene expression system for Pseudomonas (based on Sinorhizobium nod Box)

Risk assessment – GMMs, metabolic end products, and mathematical modelling.

Contact: Dr David Dowling, Project Co-ordinator, Institute of Technology Carlow;
E-mail: [email protected] ; Web: http://www.itcarlow.ie/gmrhizo/index.html