Salmonella enterica serovar Typhimurium (STM) is an invasive, facultative intracellular pathogen that resides in a specialized membrane-bound compartment termed Salmonella-containing vacuole (SCV). Essential for survival and proliferation in the SCV is Salmonella pathogenicity island II (SPI2) that encodes a type III secretion system (T3SS). The SPI2-T3SS and the effector translocation maintain SCV integrity and formation of specific tubular membrane compartments, called Salmonella-induced filaments (SIFs). The SCV/SIF continuum allows STM to bypass nutritional restriction in the intracellular environment by acquiring nutrients from the host cell. Phosphate is one of the most abundant elements in living organisms and in STM, inorganic phosphate (Pi) homeostasis is mediated by the two-component regulatory system PhoBR, resulting in expression of the high affinity phosphate transporter pstSCAB-phoU. Using fluorescent protein reporters, we investigate Pi availability for STM at single cell level over time within the intracellular habitats of different host cells. We observed that the pstSCAB-phoU encoded phosphate uptake system is essential for intracellular replication of STM because there is a Pi ion concentration less 10 micromolar within the SCV. Additionally, the demand and consumption of Pi correlates with intracellular proliferation of STM and we identify a dependency of SPI2 activity and Pi starvation.

中文翻译：

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单细胞分析显示磷酸盐的可利用性是哺乳动物宿主细胞内沙门氏菌营养的关键因素

肠炎沙门氏菌鼠伤寒沙门氏菌（STM）是一种侵入性，兼性的细胞内病原体，位于称为“含沙门氏菌的液泡”（SCV）的专门膜结合区室中。SCV中生存和增殖必不可少的是沙门氏菌致病岛II（SPI2），它编码III型分泌系统（T3SS）。SPI2-T3SS和效应器易位可维持SCV完整性并形成称为沙门氏菌诱导的细丝（SIF）的特定管状膜区室。SCV / SIF连续体允许STM通过从宿主细胞获取营养来绕过细胞内环境中的营养限制。磷酸盐是活生物体中含量最丰富的元素之一，在STM中，无机磷酸盐（Pi）稳态是由两组分调节系统PhoBR介导的，导致高亲和力磷酸盐转运蛋白pstSCAB-phoU的表达。使用荧光蛋白报道基因，我们研究了不同宿主细胞的细胞内生境中单个细胞水平上STM的Pi可用性。我们观察到pstSCAB-phoU编码的磷酸摄取系统对于STM的细胞内复制至关重要，因为SCV中的Pi离子浓度小于10微摩尔。此外，Pi的需求和消耗与STM的细胞内增殖相关，我们确定了SPI2活性和Pi饥饿的依赖性。我们观察到pstSCAB-phoU编码的磷酸盐吸收系统对于STM的细胞内复制至关重要，因为SCV中的Pi离子浓度小于10微摩尔。此外，Pi的需求和消耗与STM的细胞内增殖相关，我们确定了SPI2活性和Pi饥饿的依赖性。我们观察到pstSCAB-phoU编码的磷酸盐摄取系统对于STM的细胞内复制至关重要，因为SCV中的Pi离子浓度小于10微摩尔。此外，Pi的需求和消耗与STM的细胞内增殖相关，我们确定了SPI2活性和Pi饥饿的依赖性。