The Science

Microbes deep in the soil influence plant health by releasing potent natural antibiotics. These bacteria thrive on the roots of dryland wheat throughout the Columbia Plateau, a major wheat-producing region in Washington and Oregon. However, their role in this ecosystem has been something of a mystery. Now, a study provides direct evidence for the first time that chemicals formed by bacteria increase the formation of root-associated bacteria that help the wheat grow. These chemicals may also improve the soil.

The Impact

Dry areas like the Columbia Plateau suffer large soil losses from wind erosion, and plants often struggle to survive droughts. The availability of a natural antibiotic called phenazine-1-carboxylic acid (PCA) encourages the development of a biofilm that could combat soil degradation. How? By improving water retention. This biofilm also protects the roots from drying out during droughts. Most importantly, PCA-producing bacteria enhance long-term soil health. Knowing how these bacteria support the ecosystem may prove key to improving agriculture in the Columbia Plateau and in dryland areas around the world.


Researchers set out to discover the mechanisms that control the accumulation of PCA under dryland conditions. Led by Melissa LeTourneau, an Office of Science Graduate Student Research Fellow at Washington State University, the team included researchers from Pacific Northwest National Laboratory, University of Southern Mississippi, India’s Institute of Bioresources and Sustainable Development, U.S. Department of Agriculture Agricultural Research Service, and EMSL, the Environmental Molecular Sciences Laboratory, a Department of Energy Office of Science user facility. The researchers compared the biofilms on roots inoculated with one strain of PCA-producing bacteria to biofilms on roots lacking PCA-producing bacteria. They examined the samples using a suite of highly advanced microscopes, including EMSL’s new-generation ion microprobe, helium ion microscope, and focused ion beam/scanning electron microscope. They found PCA promotes biofilm development in dryland root systems and likely influences crop nutrition and soil health in dryland wheat fields. The results fill the gaps in our understanding of dynamics and effect of PCA in dryland agricultural ecosystems.


This work was supported by the Department of Energy’s (DOE’s) Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science user facility. Additional support was provided by the Harry E. Goldsworthy Wheat Research Fund and the Otto and Doris Amen Dryland Research Endowment administered by Washington State University, the U.S. Department of Agriculture National Institute of Food and Agriculture, the DOE Office of Science Graduate Student Research Program, the DOE Office of Science Office of Workforce Development for Teachers and Scientists, and a DOE Office of Science Early Career Research Award.


M.K. LeTourneau, M.J. Marshall, J.B. Cliff, R.F. Bonsall, A.C. Dohnalkova, D.V. Mavrodi, S.I. Devi, O.V. Mavrodi, J.B. Harsh, D.M. Weller, and L.S. Thomashow, “Phenazine-1-carboxylic acid and soil moisture influence biofilm development and turnover of rhizobacterial biomass on wheat root surfaces.” Environmental Microbiology 20, 2178 (2018). [DOI: 10.1111/1462-2920.14244]