Biochemical and genetic characterization of mechanisms used by soil bacteria to enhance plant growth

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The area around the roots of plants is rich with microbial life. Some of these microbes naturally colonize seeds and roots, and stimulate root development. This is beneficial for the plants as it increases absorption of water and soil nutrients, and helps to establish young seedlings in soil. These microbes have the potential to be applied to agricultural soil to increase crop yields. The long-term goal of my research program is to understand how beneficial soil bacteria enhance plant growth. Many bacteria produce the plant hormone indoleacetic acid and we have established that this is important for root growth stimulation by some bacteria. However, indoleacetic acid is also produced by soil bacteria that induce tumors and other lesions in plants. Differences in the amount of indoleacetic acid produced by the bacteria may explain their different effects on host plants, and therefore we will determine the environmental and molecular factors that control bacterial indoleacetic acid production. Using molecular identification techniques, we have found that the beneficial soil bacterium Pseudomonas sp. GR12-2 is most closely related to the Pseudomonas syringae group of plant pathogens. The beneficial bacterium likely has genes required for plant growth stimulation that are not present in the related pathogens and therefore we propose to sequence the genome of Pseudomonas sp. GR12-2 and compare the sequence to the known genome sequences of the closely related pathogens. Comparison of the genomes among these bacteria will reveal novel mechanisms of plant growth-promotion and will provide insight into the evolution of plant growth-promoting bacteria.