Legionella pneumophila invades protozoa with an "accidental" ability to cause pneumonia upon transmission to humans. To support its nutrition during intracellular residence, L. pneumophila relies on host amino acids as the main source of carbon and energy to feed the TCA cycle. Despite the apparent lack of a requirement for glucose for L. pneumophila growth in vitro and intracellularly, the organism contains multiple amylases, which hydrolyze polysaccharides into glucose monomers. Here we describe one predicted putative amylase, LamB, which is uniquely present only in L. pneumophila and L. steigerwaltii among the ~60 species of Legionella. Our data show that LamB has a strong amylase activity, which is abolished upon substitutions of amino acids that are conserved in the catalytic pocket of amylases. Loss of LamB or expression of catalytically-inactive variants of LamB results in a severe growth defect of L. pneumophila in Acanthamoeba polyphaga and human monocytes-derived macrophages. Importantly, the lamB null mutant is severely attenuated in intra-pulmonary proliferation in the mouse model and is defective in dissemination to the liver and spleen. Our data show an essential role for LamB in intracellular replication of L. pneumophila in amoeba and human macrophages and in virulence in vivo.

中文翻译：

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嗜肺军团菌淀粉酶对于人类巨噬细胞和阿米巴原虫的细胞内复制至关重要。

嗜肺军团菌侵入原生动物，具有“意外”能力，在传播给人类时引起肺炎。为了支持其在细胞内停留期间的营养，嗜肺军团菌依赖宿主氨基酸作为碳和能量的主要来源来供给TCA循环。尽管嗜肺军团菌在体外和细胞内生长明显缺乏葡萄糖需求，但该生物体含有多种淀粉酶，可将多糖水解成葡萄糖单体。在这里，我们描述了一种预测的推定淀粉酶 LamB，它仅存在于约 60 种军团菌中的嗜肺军团菌和斯氏军团菌中。我们的数据表明，LamB 具有很强的淀粉酶活性，当淀粉酶催化口袋中保守的氨基酸被取代时，该活性就会被消除。LamB 的缺失或 LamB 催化失活变体的表达会导致棘阿米巴和人单核细胞衍生的巨噬细胞中嗜肺军团菌的严重生长缺陷。重要的是，lamB 无效突变体在小鼠模型中的肺内增殖严重减弱，并且在传播到肝脏和脾脏方面存在缺陷。我们的数据显示 LamB 在阿米巴和人类巨噬细胞中嗜肺军团菌的细胞内复制以及体内毒力中发挥着重要作用。