Harb O S, Venkataraman C, Haack B J, Gao L Y, Kwaik Y A
Department of Microbiology and Immunology, University of Kentucky Chandler Medical Center, Lexington 40536-0084, USA.
Appl Environ Microbiol. 1998 Jan;64(1):126-32. doi: 10.1128/AEM.64.1.126-132.1998.
Invasion and intracellular replication of Legionella pneumophila within protozoa in the environment plays a major role in the transmission of Legionnaires' disease. Intracellular replication of L. pneumophila within protozoa occurs in a rough endoplasmic reticulum (RER)-surrounded phagosome (Y. Abu Kwaik, Appl. Environ. Microbiol. 62:2022-2028, 1996). Since the subsequent fate of many intracellular pathogens is determined by the route of entry, we compared the mechanisms of attachment and subsequent uptake of L. pneumophila by the two protozoa Hartmannella vermiformis and Acanthamoeba polyphaga. Our data provide biochemical and genetic evidence that the mechanisms of attachment and subsequent uptake of L. pneumophila by the two protozoan hosts are, in part, different. First, uptake of L. pneumophila by H. vermiformis is completely blocked by the monovalent sugars galactose and N-acetyl-D-galactosamine, but these sugars partially blocked A. polyphaga. Second, attachment of L. pneumophila to H. vermiformis is associated with a time-dependent and reversible tyrosine dephosphorylation of multiple host proteins. In contrast, only a slight dephosphorylation of a 170-kDa protein of A. polyphaga is detected upon infection. Third, synthesis of H. vermiformis proteins but not of A. polyphaga proteins is required for uptake of L. pneumophila. Fourth, we have identified L. pneumophila mutants that are severely defective in attachment to A. polyphaga but which exhibit minor reductions in attachment to H. vermiformis and, thus, provide a genetic basis for the difference in mechanisms of attachment to both protozoa. The data indicate a remarkable adaptation of L. pneumophila to attach and invade different protozoan hosts by different mechanisms, yet invasion is followed by a remarkably similar intracellular replication within a RER-surrounded phagosome and subsequent killing of the host cell.
嗜肺军团菌在环境中的原生动物内的侵袭和细胞内复制在军团病传播中起主要作用。嗜肺军团菌在原生动物内的细胞内复制发生在粗面内质网（RER）包围的吞噬体中（Y. Abu Kwaik，《应用与环境微生物学》62:2022 - 2028，1996）。由于许多细胞内病原体的后续命运由进入途径决定，我们比较了嗜肺军团菌被两种原生动物——蠕虫状哈特曼氏阿米巴和多食棘阿米巴附着及随后摄取的机制。我们的数据提供了生化和遗传学证据，表明这两种原生动物宿主对嗜肺军团菌的附着及随后摄取机制部分不同。首先，蠕虫状哈特曼氏阿米巴对嗜肺军团菌的摄取被单糖半乳糖和N - 乙酰 - D - 半乳糖胺完全阻断，但这些糖仅部分阻断多食棘阿米巴对嗜肺军团菌的摄取。其次，嗜肺军团菌与蠕虫状哈特曼氏阿米巴的附着与多种宿主蛋白随时间变化且可逆的酪氨酸去磷酸化有关。相比之下，感染时仅检测到多食棘阿米巴一种170 kDa蛋白有轻微去磷酸化。第三，摄取嗜肺军团菌需要蠕虫状哈特曼氏阿米巴蛋白的合成，但不需要多食棘阿米巴蛋白的合成。第四，我们鉴定出了在附着于多食棘阿米巴时严重缺陷但在附着于蠕虫状哈特曼氏阿米巴时附着仅有轻微减少的嗜肺军团菌突变体，从而为两种原生动物附着机制的差异提供了遗传学基础。数据表明嗜肺军团菌通过不同机制显著适应附着并侵入不同原生动物宿主，然而侵入后在RER包围的吞噬体内进行的细胞内复制以及随后对宿主细胞的杀伤却非常相似。
