Friday, 13 July 2018 16:26

Can Plants with Microbial Enzymes Help Clean up Excess Chemicals?

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Published in mBiosphere

Microbes and plants have both been studied as means to absorb and clean up specific chemical contaminants in a given ecosystem, a process known as bioremediation. A new Applied and Environmental Microbiology study uses a transgenic plant expressing a bacterial gene to improve the plant bioremediation activity for excess herbicide. This may be one step toward using plant-microbe combinatorial methods to clean other chemical spills. 


AppEnvMicro: Enhanced and Complete Removal of Phenylurea Herbicides by Combinational Transgenic Plant-Microbe Remediation


The research, conducted by first author Xin Yan and senior scientist Jiandong Jiang, started by cloning the Sphingobium N-demethylase pdmAB with a chloroplast transit peptide-coding region into the model plant Arabidopsis thaliana. Chloroplasts are the action site of phenylurea herbicides (PHs), where the PH is converted into an intermediate form that inhibits the chloroplast photosynthesis system and thus inhibits plant growth. 


Schematic showing experiments to test whether microbial, transgenic plants, or a combination of both will best remediate IPU-contaminated soilConceptual framework and experimental design of the transgenic plant-microbe combined remediation systems including (a) definition of 5 different treatments used, (b) testing of soil IPU levels under 5 different treatment, and (c) analysis of the bacterial community structure after each treatment. Source.

Sphingobium is a soil bacterium that can degrade a variety of aromatic compounds, including PHs, and the PdmAB gene alters the active form of the IPU and allows the plants to continuing growing in its presence. Much of the modified compounds are stored in the plant, which can grow as they accumulate, but some is secreted back into the soil. Researchers found that A. thaliana could remove PH and IPU from contaminated soils, and that the addition of Sphingobium to the soil enabled even further breakdown of the modified IPU compound. This combinatorial strategy was more successful than microbial or transgenic plant treatment alone (see schematic, right, for experimental set-up).


Why don’t the researchers simply mix the Sphyingobium or other microbes directly into the soil? While this works in some systems, it can be hard to maintain an introduced microbial population in a nonnative rhizosphere, while different plants can be engineered based on those that grow best in a given ecosystem. The deep root systems of plants also facilitate extensive reach of degradative enzymes, sometimes more than a given microbe’s niche would allow.


The authors suggest a mix of both the transgenic plants and degradative bacteria will be the most efficient way to completely remove pollutants. While the experiments were conducted with PHs, the research lays a foundation for removal of other complex organic compounds, such as those found in other herbicides or pesticides, that can be broken down by microbial enzymes. Future research may help transgenic plants to clean up and increase the safety of contaminated soils. 

Last modified on Monday, 16 July 2018 10:08
Julie Wolf

Julie Wolf is the ASM Science Communications Specialist. She contributes to the ASM social media and blog network and hosts the Meet the Microbiologist podcast. She also runs workshops at ASM conferences to help scientists improve their own communication skills. Follow Julie on Twitter for more ASM and microbiology highlights at @JulieMarieWolf.

Julie earned her Ph.D. from the University of Minnesota, focusing on medical mycology and infectious disease. Outside of her work at ASM, she maintains a strong commitment to scientific education and teaches molecular biology at the community biolab, Genspace. She lives in beautiful New York City.