In vitro and in vivo characterization of a Mycobacterium tuberculosis mutant deficient in glycosyltransferase Rv1500

In Mycobacterium marinum, the homologue of Rv1500 of M. tuberculosis encodes a glycosyltransferase. Initially, it was suggested that this gene is involved in the synthesis of phosphatidylinositol mannosides (PIMs), generating Ac2PIM7 from Ac2PIM5. Phosphatidylinositol mannoside and its related compounds lipomannan (LM) and lipoarabinomannan (LAM) have been shown to modulate the host response to an infection with M. tuberculosis. Here, we generated a deletion mutant of Rv1500 in M. tuberculosis H37Rv, and analyzed the mutant using a biochemical approach as well as in vitro and in vivo infection models. Inactivation of Rv1500 did not lead to an altered expression pattern of PIMs in M. tuberculosis H37Rv. We found phosphatidylinositol (PI), PIM2, AcPIM2, Ac2PIM2, and AcPIM6 in both strains, but were unable to detect Ac2PIM7 or Ac2PIM5 either in the wild type or the mutant strain. Uptake and growth of H37Rv and Rv1500 mutant strains in murine bone marrow-derived macrophages was identical, and TNFα and IL-12p40 production in mouse macrophages and dendritic cells was induced to similar levels following infection with either strain. Aerosol challenge of mice showed that wild type and Rv1500 mutant strains had identical growth rates in infected organs over time. We verified mRNA expression of Rv1500 in H37Rv and conclude that Rv1500 must serve a redundant role in viability and virulence of M. tuberculosis.