National Science Foundation     |     Directorate for Engineering  (ENG)
Division of Chemical, Bioengineering, Environmental, & Transport Systems  (CBET)
CBET Award Achievements 
Notable Accomplishments from CBET Awards
Engineering Plant-Microbe Symbiosis for Rhizoremediation
Wilfred Chen  -  University of California-Riverside

Background:   Many superfund sites are currently contaminated with heavy metals.  The use of plants for rehabilitation of polluted environments (phytoremediation) is an emerging area of interest because it provides an ecologically sound and safe method for restoration and remediation.  Although a number of plant species are capable of hyperaccumulation of heavy metals, the levels of removal are not effective for large-scale cleanup.
Symbiosis, from the Greek word sumbios, is defined as 'together living'.  From an ecological perspective, this occurs when several mutually beneficial species co-exist in complementary niches.  A clever alternative to phytoremediation is to combine the advantages of natural microbe-plant symbiosis into an effective cleanup technology.  It is known that many bacterial species are adapted to colonize the niche environment created by plant roots, or rhizosphere, which utilize the enzymes and nutrients exuded by the plant roots.  With the aid of biomolecular engineering, the Principle Investigators at the University of California-Riverside have harnessed this symbiotic relationship for in situ bioremediation of cadmium contamination.

Results:   The research group has successfully incorporated cadmium-binding peptides into a robust and versatile anti-fungal rhizosphere bacterium, enabling not only enhanced cadmium binding but also protection of the engineered bacteria and the colonized sunflower plants against the toxic effects of cadmium.
The versatility in adapting this strategy to different plant hosts and the ease in molecular manipulation of rhizobacteria prove to be invaluable attributes for designing plant-microbe remediation systems.  Specific biodegradation genes and plant species can be selected in accordance to the pollutants present and plant growth conditions at the toxic sites.

Winfred Chen 1     Figure 1.  Schematic of rhizoremediation

Winfred Chen 2
    Figure 2.  Rhizosphere cadmium binding experiments.  The plant morphology of 27-day old sunflower seedlings 3 days after being subjected to cadmium.  Treatments 1 and 5 were uncontaminated controls grown, while 80 mM CdCl2 were added to treatments 2 (without inoculation), 3 (incoculated with rhizobacteria), and 4 (inoculated with rhizobacteria with cadmium-binding peptides)
Credit for both Images:  Wilfred Chen, University of California-Riverside

Scientific Uniqueness:  Although the symbiotic relationship between bacteria and plants has been exploited for in situ bioremediation of a wide range of organic pollutants, very few reports today have attempted to address heavy metal remediation using this symbiotic relationship.  The most attractive feature of using rhizoremediation is the flexibility of utilizing different engineered rhizobacteria to remediate mixed-waste contaminated soil, as many superfund sites are co-contaminated with a myriad of organics and heavy metals.  The rhizosphere bacterial community can be specifically engineered to target various pollutants at co-contaminated sites in order to provide a customized rhizoremediation system.

This NSF-funded research is notable because this is the first reported rhizoremediation system, which results in an engineered symbiosis where rhizobacteria significantly reduce the toxic effects of cadmium on the growth of sunflower seedlings while it colonizes the root effectively.

This project addresses the NSF Strategic Outcome Goals, as described in the NSF Strategic Plan 2006-2011, as follows:
- 1 -   Primary Strategic Outcome Goal:      (1) Discovery:  This project employs a multi-disciplinary approach for rhizoremediation.
- 2 -   Secondary Strategic Outcome Goal:  (2) Learning:  This project provides an integrated perspective on modern biomolecular engineering to the trainees.

This Award Achievement represents Transformative Research.  It combines the field of plant sciences, biomolecular engineering and microbiology into a low-cost remediation method that integrates metabolic engineering strategies with testing in real soil settings.  This represents a unique effort that expands the fundamental development of metabolic engineering into a practical remediation technology.

Impact on Industry and/or Society:  Rhizoremediation is environmentally friendly and provides an ecologically sound and safe method for restoration and remediation.  This strategy, if successful, will provide a low-cost and environmentally benign technology for in situ heavy metal removal.  Graduate students and postdoctoral researchers participating in this research will gain an integrated perspective of the important interfaces and synergies connecting biochemistry, modern genetics, and process engineering.

Potential Economic Impact:  The current prospect for cleanup of superfund sites by physiochemical methods, standard excavation or dredging approaches are very expensive, dangerous, and intensely disruptive to the site.  The total cost of Superfund cleanup was estimated recently to be about 265 billion dollars.  Rhizoremediation is a low-cost and effective alternative since plant roots can infiltrate soils with up to 300 million miles of roots per hectare and provide remediation at much great depth without standard excavation.

Program Director:
Frederick Heineken
CBET Program Director - Biotechnology, Biochemical, and Biomass Engineering
NSF Award Number:   0331416
Award Title:   Metabolic Engineering of Root-Colonizing Bacteria for Rhizoremediation of Chlorinated Ethanes and Heavy Metals
PI Name:   Wilfred Chen
Institution Name:   University of California-Riverside
Program Element Code:   1491
CBET Award Achievement:

  FY 2008

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This Award Achievement was Updated on 14 March 2011.