An essential two-component signal transduction system in Mycobacterium tuberculosis

The bacterial two-component signal transduction systems regulate adaptation processes and are likely to play a role in Mycobacterium tuberculosis phys iology and pathogenesis, The previous initial characterization of an M. tub erculosis response regulator from one of these systems, mtrA-mtrB, suggeste d its transcriptional activation during infection of phagocytic cells. In t his work, we further characterized the mtrA response regulator from M. tube rculosis H37Rv, Inactivation of mtrA on the chromosome of M. tuberculosis H 37Rv was possible only in the presence of plasmid-borne functional mtrA, su ggesting that this response regulator is essential for M, tuberculosis viab ility. In keeping with these findings, expression of mtrA in M, tuberculosi s H37Rv was detectable during in vitro growth, as determined by S1 nuclease protection and primer extension analyses of mRNA levels and mapping of tra nscript 5' ends, The mtrA gene was expressed differently in virulent M, tub erculosis and the vaccine strain ill. tuberculosis var. bovis BCG during in fection of macrophages, as determined by monitoring of mtrA-gfp fusion acti vity. In M, bovis BCG, mtrA was induced upon entry into macrophages, In hi. tuberculosis H37Rv, its expression was constitutive and unchanged upon inf ection of murine or human monocyte-derived macrophages. In conclusion, thes e results identify mtrA as an essential response regulator gene in ill tube rculosis which is differentially expressed in virulent and avirulent strain s during growth in macrophages.