(614f) Engineering Nitrogen-Fixing Bacteria for the Rhizosphere

The rhizosphere, the soil environment adjacent to plant roots, is home to a wide variety of microorganisms that can greatly impact the physiology of nearby plants. Microbes in the rhizosphere can provide nutrients, secrete signaling compounds, and inhibit pathogens. Using Cas9 genome editing, these abilities can be manipulated to alter the agricultural performance of crops grown for food, energy, or environmental remediation. In particular, decreasing reliance on excess fertilizers can greatly decrease the energy utilization of agriculture, making cropping more efficient.

In this work, we use previously developed tools for genome editing of nitrogen-fixing bacteria to create mutants that respond to plant-relevant chemical signals. We additionally uncover the mechanisms of nitrogen regulation in a variety of different soil microbes, lending insight into robust methods for creating highly active nitrogen-fixing bacteria, even in the presence of extracellular ammonia. Finally, we engineer these bacteria to secrete natural products that decrease the activity of ammonia-oxidizing bacteria present in the soil, decreasing nitrogen leaching for crop applications. The production of excess ammonia was validated via acetylene reduction assays, and the ability of our bacteria to inhibit nitrification was determined using previously estabilished nitrification inhibition assays. These bacteria can ultimately be utilized in crop applications to decrease reliance on synthetically produced fertilizers.