LACK OF ACIDIFICATION IN MYCOBACTERIUM PHAGOSOMES PRODUCED BY EXCLUSION OF THE VESICULAR PROTON-ATPASE

The success of Mycobacterium species as pathogens depends on their abi lity to maintain an infection inside the phagocytic vacuole of the mac rophage. Although the bacteria are reported to modulate maturation of their intracellular vacuoles, the nature of such modifications is unkn own. In this study, vacuoles formed around Mycobacterium avium failed to acidify below pH 6.3 to 6.5. Immunoelectron microscopy of infected macrophages and immunoblotting of isolated phagosomes showed that Myco bacterium vacuoles acquire the lysosomal membrane protein LAMP-1, but not the vesicular proton-adenosine triphosphatase (ATPase) responsible for phagosomal acidification. This suggests either a selective inhibi tion of fusion with proton-ATPase-containing vesicles or a rapid remov al of the complex from Mycobacterium phagosomes.