HETEROGENEITY IN THE ATTACHMENT AND UPTAKE MECHANISMS OF THE LEGIONNAIRES-DISEASE BACTERIUM, LEGIONELLA-PNEUMOPHILA, BY PROTOZOAN HOSTS

Invasion and intracellular replication of Legionella pneumophila withi n protozoa in the environment plays a major role in the transmission o f Legionnaires' disease. Intracellular replication of L. pneumophila w ithin protozoa occurs in a rough endoplasmic reticulum (RER)-surrounde d phagosome (Y. Ahu Kwaik, Appl. Environ. Microbiol. 62:2022-2028, 199 6). Since the subsequent fate of many intracellular pathogens is deter mined by the route of entry, we compared the mechanisms of attachment and subsequent uptake of L. pneumophila by the two protozoa Hartmannel la vermiformis and Acanthamoeba polyphaga. Our data provide biochemica l and genetic evidence that tie mechanisms of attachment and subsequen t uptake of L. pneumophila by the two protozoan hosts are, in part, di fferent. First, uptake of L. pneumophila by H. vermiformis is complete ly blocked by the monovalent sugars galactose and N-acetyl-D-galactosa mine, but these sugars partially blocked A. polyphaga. Second, attachm ent of L. pneumophila to H. vermiformis is associated with a time-depe ndent and reversible tyrosine dephosphorylation of multiple host prote ins. In contrast, only a slight dephosphorylation of a 170-kDa protein of A. polyphaga is detected upon infection. Third, synthesis of H., v ermiformis proteins but not of A. polyphaga proteins is required for u ptake of L. pneumophila. Fourth, we have identified L. pneumophila mut ants that are severely defective in attachment to A. polyphaga but whi ch exhibit minor reductions in attachment to H. vermiformis and, thus, provide a genetic basis for the difference in mechanisms of attachmen t to both protozoa. The data indicate a remarkable adaptation of L. pn eumophila to attach and invade different protozoan hosts by different mechanisms, yet invasion is followed by a remarkably similar intracell ular replication within a RER-surrounded phagosome and subsequent kill ing of the host cell.