The cell envelope of Mycobacterium tuberculosis contains
glycans and
lipids of peculiar structure that play prominent roles in the biology and pathogenesis of
tuberculosis. Consequently, the chemical structure and biosynthesis of the cell wall have been intensively investigated in order to identify novel
drug targets. Here, we validate that the function of phosphatidyl-myo-
inositol mannosyltransferase PimA is vital for M.
tuberculosis in vitro and in vivo.
PimA initiates the biosynthesis of phosphatidyl-myo-
inositol mannosides by transferring a mannosyl residue from
GDP-Man to phosphatidyl-myo-
inositol on the cytoplasmic side of the plasma membrane. To prove the essential nature of
pimA in M.
tuberculosis, we constructed a
pimA conditional mutant by using the TetR-Pip off system and showed that downregulation of
PimA expression causes bactericidality in batch cultures. Consistent with the biochemical reaction catalyzed by
PimA, this phenotype was associated with markedly reduced levels of phosphatidyl-myo-
inositol dimannosides, essential structural components of the mycobacterial cell envelope. In addition, the requirement of
PimA for viability was clearly demonstrated during macrophage
infection and in two different mouse models of
infection, where a dramatic decrease in viable counts was observed upon silencing of the gene. Notably, depletion of
PimA resulted in complete clearance of the mouse lungs during both the acute and chronic phases of
infection. Altogether, the experimental data highlight the importance of the phosphatidyl-myo-
inositol mannoside biosynthetic pathway for M.
tuberculosis and confirm that
PimA is a novel target for future
drug discovery programs.