This application will utilize biochemical and molecular genetic approaches to examine the virulence factors of the oral spirochete Treponema denticola. Since the motility of these organisms appears to be an important factor in the pathogenicity of the organisms, the mechanisms of chemotaxis in the spirochete will be investigated. Based upon the recent isolation in this laboratory of two T. denticola genes which are homologous to the methyl-accepting chemotaxis proteins of other bacteria, the respective roles of the two genes in motility will be examined. Mutants defective in each gene will be constructed utilizing a gene inactivation system recently developed in this laboratory and examined for defects in chemotaxis as well as in invasion through the extracellular matrix. Extracellular vesicle formation in gram-negative bacteria, including T. denticola, appears to play a role in invasiveness and nutrition of the organisms. However, little information is currently available concerning the molecular basis for the expression of the vesicles. Therefore, studies are proposed to examine the role of the stringent response in regulating the expression of vesicles in the oral spirochete. The role of the relA gene in this process will be investigated following isolation, characterization, and mutagenesis of the gene. Since a number of virulence-associated spirochetes cannot be readily cultivated in the laboratory, the recent development of a gene transfer system in T. denticola in this laboratory now makes it feasible to clone genes from the former organisms into the oral spirochete. In order to evaluate the potential for the construction of such model systems, selected genes from the syphilitic spirochete Treponema pallidum will be expressed in T. denticola. Such systems can serve as model systems for assessing the virulence potential of organisms which cannot be easily manipulated in vitro.