Signals affecting the urease status of plant-associated bacteria, Methylobacterium spp

This research focused on furthering our understanding of the interactions between PinkPigmented Facultative Methylotrophic bacteria (PPFMs) and plants. PPFMs (Methylobacterium spp.) have been found to be the most abundant microorganisms among phylloplane microflora, and have been recovered from all plants examined. I focused on the plant influence on production of active PPFM urease. Arabidopsis thaliana and Glycine max (soybean) are two dicots which provide valuable ureasenegative mutants. However, while genetic and genomic analysis of each plant are advancing, little is known about the identity of the PPFMs with which they associate. I established phylogenetic relationships of various PPFM isolates recovered from plants and elsewhere. I examined the ability of resident PPFMs to mimic the urease-negative phenotype of two mutant classes of urease-negative soybean hosts. The working model is that there is a signal from the plant that either inhibits the production of the urease gene products in the associated bacteria or inhibits the function or transport of Ni 2+ from the plant to the bacteria. This signal could be a nitrogenous signal (ureides, urea, ammonia) or simply a block in Ni 2+ transport from the plant or plant cell to the associated bacteria. Examination of urease expression in planta or in culture requires knowledge of the urease genes and the regulation of urease in the PPFMs. Urease expression is directly related to