Estudio de la implicación de los genes Rv0576-Rv0577 en la tinción con rojo neutro y la virulencia de Mycobacterium tuberculosis

Abstract

The identification of Mycobacterium tuberculosis virulence factors is necessary to develop new drugs and vaccines, urgently needed to fight an infectious disease that causes 1.7 million deaths annually. A unique feature of the virulent strains of M. tuberculosis is their ability to fix the neutral red stain in its acid form. Although sulfolipid (a component of the cell envelope) was first recognized as the molecule responsible for the neutral red uptake, recent studies have refuted this relationship, and have established that the Rv0577 gene, which constitutes a single operon together with the putative transcriptional regulator Rv0576, provides M. smegmatis (a saprophytic mycobacteria) with the neutral red positive phenotype characteristic of M. tuberculosis virulent strains. In the present work, by means of transcriptional fusions and microarray analysis, we have proved that the Rv0576 gene indeed behaves as a transcriptional regulator that represses the expression of the Rv0576-Rv0577 operon. However, studies of mutant and complemented strains in these genes have shown that none of them is necessary either for the neutral red reaction of M. tuberculosis or for virulence in the murine infection-model. We have also proved that, in vitro, M. tuberculosis forms heterogeneous cell populations regarding the neutral red character and the synthesis of phthiocerol dimycocerosates, a cell-wall lipid related to the virulence of the bacillus. Reversion of the spontaneous neutral red mutants to the wild-type phenotype occurs at certain frequency, whereas reversion of the mutants in the synthesis of phthiocerol dimycocerosates has not been detected and they accumulate with successive cultures of M. tuberculosis, becoming the bulk of the population. As both the neutral red character and phthiocerol dimycocerosates are related to M. tuberculosis virulence, it would be prudent to check these phenotypes before analyzing the virulence of a certain strain or mutant of M. tuberculosis.

Date of Award	25 May 2007
Original language	Undefined/Unknown
Supervisor	Isidre Gibert Gonzalez (Director)