Our research group studies different aspects of epiphytic bacteria that live on the surface of healthy plants. We study bacteria active in ice nucleation (Ice+), thereby causing frost damage to plants, as well as plant pathogenic bacteria inhabiting plant surfaces before infection. Our research emphasizes both molecular genetic and ecological approaches to studying how epiphytic bacteria interact with other microorganisms on plants as well with the plants themselves. We seek to better understand the adaptations that epiphytic bacteria have evolved to exploit this unique habitat.

Our work involves both field and laboratory studies. We ascertain the habitat in which epiphytes live and how much they modify this habitat. We produce "biological sensors" consisting of ice nucleation reporter genes driven by environmentally responsive promoters to assess the activity of particular genes in situ. These tools let us examine physical and environmental features of microhabitats in which bacteria live on leaves. In addition, we determine the fitness of random transposon mutants on leaves. We clone and sequence the genetic loci identified as required for survival to determine the phenotypes they confer.

We exploit the gene encoding Green Fluorescent Protein (GFP) as a reporter gene to determine the transcription of particular genes in individual cells in natural habitats. This work involves fluorescent microscopic visualization of cells harboring gene fusions to GFP, followed by quantitative analysis of the fluorescence intensity of individual cells. Thus, we can examine variation in habitat composition and observe microbial activities at the very small scales meaningful for bacterial colonists of plants.

We have developed methods to identify which bacterial genes get expressed only on plant surfaces. We work to characterize these genes since they encode traits important to the epiphytic fitness of bacteria.

More recently, we initiated research to determine the nature and significance of cell-to-cell communication between bacteria on plants. We study the extent to which bacteria sense the presence of neighboring cells via interaction with small diffusible signal molecules. We study which traits bacteria express in a signal density-dependent fashion. We seek environmentally friendly ways to disrupt bacterial signaling to control frost damage and diseases incited by epiphytic bacteria.