Metabolism of phytate and inositol by Legionella and implications for bacterial virulence

嗜肺军团菌是一种环境细菌，可引起严重的肺炎，称为“军团病”。嗜肺乳杆菌是一种兼性细胞内病原体，生长在营养液中，也生长在肺中自由生活的变形虫和巨噬细胞中。氨基酸被认为是嗜肺乳杆菌的主要碳和能量来源。然而，基因组序列、转录组数据和代谢研究表明，嗜肺乳杆菌具有广泛的代谢能力，也利用碳水化合物。为了在细胞内复制，嗜肺乳杆菌向宿主细胞分泌靶向磷酸肌肽（PI）脂质的“效应蛋白”。易位的PI磷酸酶在结构上与植酸酶（肌醇六磷酸磷酸酶）相关，这增加了双重功能酶直接与嗜肺乳杆菌的代谢和毒力相关的可能性。在这个应用中，我们建议分析(i)嗜肺乳杆菌在细胞外和细胞内以植酸盐和肌醇作为磷、碳和/或能量来源的生长，（ii）嗜肺乳杆菌PI磷酸酶的活性和分泌，（iii）嗜肺乳杆菌突变株缺乏参与植酸盐或肌醇代谢的基因，（iv）受感染变形虫体内植酸盐或肌醇代谢的亚细胞区隔化。(v)嗜肺乳杆菌降解[13C]植酸盐和[13C]肌醇的同位素谱。

The environmental bacterium Legionella pneumophila causes a severe pneumonia termed “Legionnaires’ disease”. L. pneumophila is a facultative intracellular pathogen that grows in nutrient broth, as well as in free-living amoebae and macrophages in the lung. Amino acids are regarded the prime carbon and energy source of L. pneumophila. However, the genome sequence, transcriptome data and metabolism studies indicate that L. pneumophila possess broad metabolic capacities and also utilizes carbohydrates. To replicate intracellularly, L. pneumophila secretes into host cells “effector proteins” that target phosphoinositide (PI) lipids. A translocated PI phosphatase is structurally related to phytases (myo-inositol hexakisphosphate phosphatases), raising the possibility that a dual function enzyme directly links metabolism and virulence of L. pneumophila. In this application, we propose to analyze (i) extra- and intracellular growth of L. pneumophila on phytate and inositol as a source of phosphorus, carbon and/or energy, respectively, (ii) phytase activity and secretion of an L. pneumophila PI phosphatase, (iii) L. pneumophila mutant strains lacking genes involved in phytate or inositol metabolism, (iv) subcellular compartmentalization of phytate or inositol metabolism in infected amoebae, and (v) the isotopologue profiles of [13C]phytate and [13C]inositol degradation by L. pneumophila.