Endophytic degrader bacteria for improving phytoremediation of organic xenobiotics: Final Report DRAFT

This project represented a completely new approach towards improving the technology of phytoremediation of soil and groundwater contaminated with water soluble and volatile compounds. It endeavoured to tackle the problem of inefficient degradation of these compounds during phytoremediation by improving their degradation during transport in the plant vascular system. Introducing endophytic degrader bacteria into the plants’ vascular system was proposed as a tool to achieve this goal.
As a scientific necessity, the project comprised the thorough ecological and genetic investigation of endophytic bacteria, and the isolation of a large number of natural endophytic strains. The project delivered on this goal by providing a large collection of 150 novel characterized endophytic bacteria from poplar and willow, two plant species commonly used for phytoremediation, and from Flag Iris, a plant used for the novel technology of constructed wetlands. Several of these bacteria were engineered to degrade specific organic contaminants, including BTEX, TCE, 2,4-D and naphthalene.
Central to the whole project was the goal to reveal the potential of endophytic inoculants for improving phytoremediation in terms of
■ plant survival (decreased phytotoxicity of the pollutant) and contaminant removal (bacterial degradation), resulting in reduced accumulation of contaminants, their metabolites (misrouting products), or their release in the environment via plant transpiration.
Work completed with the Yellow Lupin / Burkholderia cepacia / toluene model
demonstrates clearly that ! the inoculated endegrader (endophytic bacterial degrader) protects the plant from chemical toxicity, by degrading the toxic compound (the phytoprotection aspect of the “ENDEGRADE concept”),
■ the inoculated endegrader strongly reduces the emission of the chemical from the test system, by a more complete degradation of the compound (the environmental remediation aspect of the “ENDEGRADE concept”),
■ the observed effects are not due to rhizosphere colonising or soil inhabiting bacteria.
Thereby the project delivered on its central goal, and confirmed the somewhat daring project hypothesis, for which there had been only scarce evidence at the time the project was conceived.
As an unexpected result of the project, now we better understand the limitations of phytoremediation:
■ TBT does not get taken up by plants,
■ TCE and toluene do not get degraded by plant tissues.
These findings explain some of the hitherto inexplicable problems that phytoremediation researchers have had with these two compounds.
A spin-off of the project was the unexpected transfer of a mathematical uptake model, developed for intact plants, to human tissues and cancer cells. It appears that—as a byproduct of this project—the design of new chemotherapeutic drugs can be accelerated significantly, because using a mathematical uptake model will avoid lengthy screening steps with human tumor cell cultures. This invention was not patented and can be utilised free of charge.
Another potential spin-off of the project was the unexpected generation of constitutive TCE degraders, i.e., bacteria that do not require toluene or phenol for induction of cometabolic TCE degradation. Genetic engineering methods were not involved in the generation of this metabolic trait. The business potential of this new biotechnology is under evaluation.