Team:UIUC Illinois/Description
MOTIVATION AND DESCRIPTION
Living in the Midwest, pesticides and herbicides used in agriculture have a large impact on our local environment. As of 2016, Illinois was responsible for 8.56% of the total volume of glyphosate applied in the United States. Glyphosate is the main ingredient in formulations such as RoundupTM and has recently been in the news for being classified as a probable carcinogen by the International Agency for Research on Cancer (IARC). The IARC, which is part of the World Health Organization (WHO), has determined in 2015 that glyphosate is a Group 2A carcinogen. This conclusion has been based on extensive research of over 1000 studies. This included experimental studies on cancer as well as cancer-related effects in environmental systems. Additionally, it was determined that the other chemicals in the herbicide formulation are not carcinogenic. Glyphosate has potential to impact the environment given its liberal usage, and its ability to persist after application. In fact, it has a reported half-life of anywhere from two days to twenty years.
The mechanism by which glyphosate has been determined to be problematic due to the fact that it is a glycine derivative. Specifically, glyphosate, or N-phosphonomethyl-glycine, has a phosphonomethyl group in place of one of the hydrogens found in glycine. This alteration affects plant metabolism by blocking the activity of the enzyme enolpyruvylshikimate-3-phosphate-synthase (EPSPS) and its function in the shikimic acid pathway. This enzyme is located in the chloroplasts of plants, and plays a key role in the conversion of glycolysis and pentose pathway carbohydrates/precursors to aromatic amino acids and many other important plant metabolites. Since glyphosate is an inhibitor of EPSP synthase, binding where glycine typically would, it inhibits the shikimic acid pathway, causing a deficiency in aromatic amino acids and ultimately leading to plant death. Since this enzyme is highly conserved in higher plants, glyphosate is a broad-spectrum herbicide. Additional chemicals in the Roundup formulation increase its efficiency by speeding up uptake time via surfactants and increasing overall solubility by turning it into a salt ("Glyphosate: Mechanism of Action").
We decided to research how glyphosate can be degraded into nontoxic components for the basis of our project. Particularly, we focused on the prospects of glyphosate degradation in bodies of water. Glyphosate contamination in sites such as this can be highly problematic because glyphosate shows little propensity toward hydrolytic decomposition (half life >35 days) and there are few microorganisms in water that can degrade it.
Our general project is based on a degradation pathway found in Pseudomonas pseudomallei 22, a pathogenic bacterium naturally found in the soil. Two genes, glpA and glpB, were identified as increasing tolerance to glyphosate and enabling the breakage of the C-N bond, resulting in the formation of AMPA. We plan to clone these genes into E. coli to enable it to degrade glyphosate. In E. coli AMPA can be further broken down into phosphorus and methylamine by a native C-P lyase. Through this, we hope to create E. Coli that can break down glyphosate in different environments such as water or soil.
References "Glyphosate: Mechanism of Action." Glyphosate Facts, 19 June 2013, http://www.glyphosate.eu/glyphosate-mechanism-action.
USGS. "Estimated Agricultural Usage of Glyphosate." 2016 Pesticide Use Maps , 2016, water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2016&map=GLYPHOSATE&hilo=L.
Battaglin, William A, et al. "Common Weed Killer Is Widespread in the Environment." Common Weed Killer Is Widespread in the Environment, 2014, toxics.usgs.gov/highlights/2014-04-23-glyphosate_2014.html.
Penaloza-Vazquez, A., Mena, G. L., Herrera-Estrella, L., & Bailey, A. M. (1995). Cloning and Sequencing of the Genes Involved in Glyphosate Utilization by Pseudomonas pseudomallei. Applied and Environmental Microbiology,61, 538-543.
