Superfund Research Program
Phytoremediation of Pollutants Using Transgenic Plants
Project Leader: Stuart E. Strand
Grant Number: P42ES004696
Funding Period: 2006-2015
An experiment to compare the abilities of transgenic and wild-type poplar expressing the mammalian cytochrome P450 2E1 (CP4502E1) to phytoremediate groundwater contaminated with trichloroethylene (TCE) under field conditions is ongoing. Planted and control beds were dosed with TCE, and effluent and soil samples were analyzed. During the last season, the researchers found that significantly more TCE was lost in the planted beds than in the unplanted beds, although loss of water in the planted beds was high enough that effluent concentrations were higher than in the unplanted beds. Preliminary data showed that TCE recovery from the transgenic tree beds was lower than the wild-type tree beds, indicating that transgenic trees increased the removal of TCE under field conditions. Dehalococcoides 16S genes were detected, but associated functional genes tceA, vcrA, and bvcA were not found. qPCR analysis of DNA samples showed that functional genes etnC and etnE associated with aerobic oxidation of vinyl chloride were present. These data suggest that TCE was removed by reductive dechlorination of TCE to dichloroethene and vinyl chloride, followed by oxidation to CO2. The researchers are analyzing chloroethenes in soils to obtain a better chloroethenes accounting. They will quantify the presence of dehalogenase genes, 16S genes of dechlorinators, and etnC and etnE functional genes using qPCR.
A second component of this project is an investigation of the insecticide chlorpyrifos. Development of superior tree varieties could help protect riparian zones, preventing the chlorpyrifos from entering water systems. Development of a cost-effective production system for active chlorpyrifos-degrading enzymes could help in onsite emergency treatment of spills.
Seven poplar and willow varieties were screened for uptake of chlorpyrifos. All seven were able to remove the pollutant, but specific willow lines removed the pesticide faster. The plants also translocated chlorpyrifos throughout the plant and degraded it to near completion over several weeks. These results were published this year in the International Journal of Phytoremediation.
Efforts to improve the remediation capacity of poplar using transgenic technologies have not been successful. Although the mammalian genes, PON1 and CYPB6 for chlorpyrifos degradation were inserted in the nuclear genome of poplar and the chloroplast genome of tobacco and these transgenes were effectively transcribed, no active enzyme has been detected. The transgenic plants do not have increased removal of the pesticide from solution or reduced phytotoxicity. The researchers are currently conducting studies to determine where the system is blocked, either protein production or active enzyme formation.
Studies of uptake of volatile organic compounds (VOCs) from the air by transgenic plants. With the help of two talented undergraduate volunteers, the researchers have resumed efforts to engineer CYP4502E1 into a houseplant, pothos ivy, and to determine whether increased stomatal opening increases uptake of VOCs. Transformed pothos is presently regenerating from callus tissue cultures. Arabidopsis mutants with increased stomata have been transformed with the CYP4502E1 gene and are presently being screened.