Aerial plant surfaces support diverse populations of epiphytic bacteria including ice-nucleation-active Pseudomonas syringae strains. Previous studies indicate that P. syringae strains compete for the same limiting resource in the phyllosphere, but exhibit differences in their relative competitive ability and their degree of coexistence. One P. syringae strain investigated showed a high degree of coexistence with other epiphytic bacterial species, including Xanthomonas maltophilia and Erwinia herbicola. The proposed research will examine the role of resource partitioning in the coexistence of bacterial epiphytes, particular differential site occupation and different nutrient utilization. The spatial distribution of coexisting epiphytes will be examined using immuno-fluorescence and immuno-electron microscopy. Further, the role of aggregation and site independence will be addressed using a binary sensing system based on bioluminescence and the diffusion of an activator from one strain to another. The role of different nutrient utilization in coexistence will be investigated using naturally occurring P. syringae strain pairs and isogenic P. syringae strains altered in specific metabolic capabilities. The use of manipulated isogenic strains will provide a powerful tool in these investigations of resource partitioning. The investigators will use innovative and carefully-executed molecular techniques to investigate the importance of resource partitioning in determining coexistence in bacterial communities.
