This proposal outlines a career development plan that consists of intensive research experience and didactic training in bacterial pathogenesis. The institutional environment is scientifically rich and well suited for the training of young physician-scientists. The ultimate goal of this period of intensive research training is to train the candidate as an independent investigator on a medical school faculty. Tuberculosis, caused by Mycobacterium tuberculosis, is the single leading cause of death from an infectious disease in the world today. Three million die each year from Tuberculosis and one third of the world's population is infected with M. tuberculosis MTB. The cell envelope of MTB is a complex structure composed of hydrophobic lipids, mycolic acids, cord factors, and Lipoarabinomannan and is thought to contribute to the virulence of the organism. Despite substantial investigation into the ultrastructure and chemical composition of the mycobacterial cell envelope, the contribution of specific cell walls constituents to mycobacterial virulence remains poorly defined. The importance of the cell envelope to the viability of the mycobacterial cell is emphasized by the observation that several antimycobacterial drugs including Isoniazid are thought to exert their bacteriacidal effect through inhibition of cell envelope biosynthesis. This proposal outlines a series of experiments designed to investigate the role of the cell envelope of MTB in pathogenesis through the generation and characterization of mycobacterial mutants deficient in the synthesis of cell envelope constituents. Using a recently developed transposon mutagenesis system, a series of insertional mutants will be generated and screened for alterations in their cell envelope composition. Morphologic, immunologic, and functional approaches to the isolation and characterization of cell envelope altered mutants will be used. Isolation and characterization of such mutants will likely yield important insights into the role of the mycobacterial cell envelope in the pathogenesis of Tuberculosis and the interaction of the tubercle bacillus with host cells.