|Lerch, Robert - Bob|
Submitted to: North American Agroforestry Conference
Publication Type: Proceedings
Publication Acceptance Date: 5/15/2009
Publication Date: 5/31/2009
Citation: Lin, C., Thompson, B.M., Hsieh, H., Lerch, R.N., Kremer, R.J., Garrett, H.E. 2009. Introduction of Atrazine-Degrading Pseudomonas sp. Strain ADP to Enhance Rhizodegradation of Atrazine. North American Agroforestry Conference, May 31-June 3, 2009, p. 183-190. Interpretive Summary: The corn herbicide atrazine has been widely used for weed control in U.S. corn production for decades. However, public health and ecological concerns have been raised because of contamination of surface and ground water by atrazine and its breakdown products, which may be toxic to humans and aquatic life. Phytoremediation is an environmental mitigation technique in which plants are used to reduce the levels of contaminants in soil. Ongoing research has identified some promising plant species for reducing atrazine in soils, but the plants alone cannot completely breakdown atrazine into harmless byproducts. In an effort to achieve complete atrazine degradation, ARS and University of Missouri researchers investigated the potential of adding a bacterium, Pseudomonas species ADP, to soils along with three plant species known to enhance atrazine degradation. This bacterium was isolated from an atrazine spill site, and it contains a series of genes known to be responsible for complete degradation of atrazine. When added to soil containing atrazine, the Pseudomonas bacterium degraded all atrazine within three days, and 35 to 40% of atrazine was accounted for as carbon dioxide within ten days, indicating complete degradation of the atrazine and its breakdown products. In addition, a newly developed DNA-based method was successfully used in soils to monitor the persistence of the atrazine degrading gene contained in the Pseudomonas bacterium. This research could have a significant benefit as an atrazine remediation technique that will result in decreased contamination of water resources by this commonly used herbicide.
Technical Abstract: The herbicide atrazine (ATR) has been widely applied to fields in the U.S. and Midwestern states, resulting in contamination of surface and ground waters. Public health and ecological concerns have been raised due to the toxicity and potential carcinogenic or endocrine disrupting effects of ATR and its metabolites. Ongoing research has identified plant species that can enhance degradation of ATR in rhizosphere soil. However, the mineralization of ATR and its chlorinated metabolites was limited to <10% under both laboratory and field conditions. Pseudomonas sp. strain ADP (P. ADP) is a bacterium containing a series of genes responsible for complete ring cleavage and rapid mineralization of ATR into carbon dioxide. We investigated the synergistic effect of adding P. ADP to the rhizosphere soil of atrazine degrading plants in an effort to achieve more complete ATR degradation in soils. An experiment was conducted in a walk-in growth chamber with three plant treatments: 1) hybrid poplar clones (Populus deltoides X Populus nigra, clones 80X01038); 2) switchgrass (Panicum virgatum L.) and 3) eastern gammagrass (Tripsacum dactyloides). A control treatment with no plants was also included. Rhizosphere soil was separated from the plants, and 14C-ATR and P. ADP were then added. A treatment without P. ADP was setup as a control for each plant treatment. The herbicide treated soil was then incubated for two weeks at 25oC in the dark. The P. ADP treatments degraded all atrazine within 3 days regardless of plant treatment, and 35 to 40% of the atrazine was accounted for as CO2 within 10 days, indicating complete degradation of the ATR and its metabolites. In addition, a highly sensitive quantitative real-time PCR technique was successfully applied to monitor changes in the copy number of the atzA gene in soils. The addition of P. ADP into the rhizosphere of vegetative buffers could lead to an effective atrazine remediation technique that will result in decreased contamination of water resources by this commonly used herbicide.