Our research group has focused on the molecular microbial ecology of plant-associated bacteria. While relatively un-studied, microorganisms that live on plant surfaces are enormously important in that this habitat serves as a reservoir of microbes that can infect the plants on which they live, can injure plants by acting as catalysts for ice formation (ice nucleation activity), and by producing plant hormones that can alter the normal pattern of plant development. As model systems I have focused much of this effort on the plant pathogenic bacterium Pseudomonas syringae, and the saprophytic bacterium Erwinia herbicola (Pantoea agglomerans) on plant surfaces. These are two of the bacteria that are most commonly found on plants. They offer the opportunity to compare and contrast the growth and survival tactics employed by pathogenic and non-pathogenic bacteria on the surface of healthy plants.
More recently the lab is also addressing the endophytic growth of bacteria within plants. In these studies we are comparing the strategies used by P. syringae, a facultative pathogen of plants that can multiply within the intercellular spaces of plant tissues without causing disease symptoms with that of Xylella fastidiosa, an obligate colonist of xylem vessels. To address these questions my program has developed and applied a variety of molecular genetic tools for the study of these bacteria while in their natural habitats in and on plants. Our studies of plant-associated bacteria have revealed that the interactions between the bacteria and the plant are, in fact, strongly conditioned by bacterial traits that were a result of their interaction with each other. We now have several major projects that address a variety of cell density-dependent traits in bacteria that mediate their growth and survival in and on plants. This exciting new research area promises to provide a new perspective on the way we visualize plant-microbe interactions and to provide new strategies to manage the diseases caused by plant pathogenic bacteria