Characterization of different aspects of Mycobacterium tuberculosis physiology: impact on drug discovery and virulence

Mycobacterium tuberculosis is a remarkably successful human pathogen, which causes nearly two million death annually. Although tuberculosis has been widely studied for more than a century, the mechanisms by which it causes the disease, are poorly understood. Recent progress of molecular genetics beside of completion of its genome sequence, have been providing tools for new approaches to a better understanding of M.tuberculosis biochemistry, physiology and pathogenesis. Here we show a series of studies in which, taking advantage of a genetic approach, we characterized different aspects of M. tuberculosis physiology which might have a strong impact in drug discovery and in the understanding of its virulence mechanism. Producing a knock-down mutant of sigA, encoding the principal sigma factor of M. tuberculosis, we showed that it is essential and posed the basis for the development of a simple in vitro test to select molecules active on dormant bacteria. Similar results were obtained using .a genetic system in which the expression of different toxins belonging to toxin-antitoxin modules can be induced. We also produced an M. tuberculosis mutant in which the gene encoding the alternative sigma factor SigE and its cognate anti-sigma factor RseA were deleted. The SigE-RseA regulatory network is extremely important to stop phagosome maturation and consequently for virulence. This mutant strain will be complemented with the sigE-rseA couple carrying different mutations that will allow the further characterization of this regulatory network. Finally, we also characterized the regulation of the expression of the PE_PGRS30 structural gene and the role of its PGRS domain in virulence. Keywords: M.tuberculosis, sigA, sigE, Toxin-antitoxin, PE_PGRS