Grantee Research Project Results
2000 Progress Report: Development of Novel Bioadsorbents for Heavy Metal Removal
EPA Grant Number: R827227Title: Development of Novel Bioadsorbents for Heavy Metal Removal
Investigators: Chen, Wilfred , Mulchandani, Ashok , Mehra, Rajesh
Institution: University of California - Riverside
EPA Project Officer: Aja, Hayley
Project Period: December 1, 1998 through November 30, 2001
Project Period Covered by this Report: December 1, 1999 through November 30, 2000
Project Amount: $360,818
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management , Sustainable and Healthy Communities
Objective:
The overall objective of this research is to develop high-affinity microbial bioadsorbents for heavy metal removal. Genetically engineered E. coli with surface-expressed peptide analogues (ECs) of phytochelatin will be utilized as microbial bioadsorbents for the removal of heavy metals. A series of synthetic genes encoding ECs ranging two to twenty cysteine will be expressed on the cell surface, enabling metal sequestration in the absence of uptake. Recombinant bacteria which exhibit the best selectivity and affinity for heavy metal accumulation will be co-expressed with the cellulose binding domain (CBD) protein on the cell surface and use for developing bioadsorbent columns with cellulose-based support.Progress Summary:
The effect of pH and temperature on whole cell immobilization via surface-expressed CBD was first investigated. Cells with CBD on the surface bound much stronger to the cellulose fiber than the control cells at a pH higher than 6.0. These results agreed very nicely with the pH binding profile of CBD. In contrast to CBD, which has the highest affinity at 4°C, our results indicated that binding at 37°C actually provided the highest whole cell immobilization. These results suggest that 37°C may be an ideal temperature not only for the metal removal but may also be true for cell immobilization. The number of CBD molecules anchored on the cell surface could also influence that whole cell binding to cellulose. A regulated expression system was employed to fine-tune the expression of CBD to the cell surface. Whole cell binding increased with higher CBD expression until binding is saturated. This result suggests that even a low level of CBD may be sufficient to provide maximum cell immobilization efficiency.
To demonstrate the benefit of expressing ECs on the cell surface, EC20 was expressed intracellularly as a fusion with the maltose-binding protein (MBP-EC20). The expression level of MBP-EC20 fusions (47kDa) was more than 10 times higher than expression on the cell surface; however, the amount of Cd2+ accumulated by cells with EC20 anchored on the surface was almost twice the amount in cells with EC20 expressed intracellularly. This phenomenon may be attributed to the limitation in metal uptake resulting in most of the cysteine binding sites being either vacant or oxidized. To demonstrate that metal uptake is the rate-limiting step, E. coli strains were engineered to coexpress the mercury transport proteins, MerP and MerT, with MBP-EC20. The presence of mercury transport proteins enhanced the accumulation of mercury by almost 5-fold. This result suggests that the coexpression of metal transporter may be an alternative solution to significantly increase the bioaccumulation of heavy metals.
Future Activities:
In the third year, we will focus on co-expression of CBD and EC20 on the cell surface. The goal is to fine-tune the ratio of CBD and EC20 in order to achieve the optimal cell binding and metal binding capability. We will also establish bioreactor column with either immobilized cells or peptides for the continuous removal of heavy metals.Journal Articles on this Report : 2 Displayed | Download in RIS Format
| Other project views: | All 18 publications | 10 publications in selected types | All 10 journal articles |
|---|
| Type | Citation | ||
|---|---|---|---|
|
|
Bae W, Chen W, Mulchandani A, Mehra RK. Enhanced bioaccumulation of heavy metals by bacterial cells displaying synthetic phytochelatins. Biotechnology and Bioengineering 2000;70(5):518-524. |
R827227 (2000) R827227 (Final) |
not available |
|
|
Wang AA, Mulchandani A, Chen W. Whole-cell immobilization using cell surface-exposed cellulose-binding domain. Biotechnology Progress 2001;17(3):407-411 |
R827227 (2000) R827227 (Final) |
Exit Exit |
Supplemental Keywords:
environmental biotechnology, bioremediation, pollution prevention, waste reduction, treatment, bioadsorbant, heavy metal removal, genetic engineering., Air, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Water, Waste, Toxics, National Recommended Water Quality, Engineering, Mercury, Environmental Chemistry, Engineering, Chemistry, & Physics, Bioavailability, Bioremediation, heavy metals, wetland, bioadsorbent, phytochelation, regulatory standards, water quality, organophospherous hydrolase, lead, bioremediation model, cadmium, biological attenuation, aquatic, bioadsorption, fate and transport, synthetic genes, wastewater treatment, waste reduction, chemical transport, chemical speciation, cellulose binding, mercury concentrationsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.