Alpuche Aranda C M, Swanson J A, Loomis W P, Miller S I
Infectious Disease Unit, Massachusetts General Hospital, Boston 02114.
Proc Natl Acad Sci U S A. 1992 Nov 1;89(21):10079-83. doi: 10.1073/pnas.89.21.10079.
Survival of Salmonella typhimurium within macrophage phagosomes requires the coordinate expression of bacterial gene products. This report examines the contribution of phagosomal pH as a signal for expression of genes positively regulated by the S. typhimurium virulence regulators PhoP and PhoQ. Several hours after bacterial phagocytosis by murine bone marrow-derived macrophages, PhoP-activated gene transcription increased 50- to 77-fold. In contrast, no difference in PhoP-activated gene expression was observed after infection of cultured epithelial cells, suggesting that the membrane sensor PhoQ recognized signals unique to macrophage phagosomes. The increase in PhoP-regulated gene expression was abolished when macrophage culture medium contained NH4Cl or chloroquine, weak bases that raise the pH of acidic compartments. Measurements of pH documented that S. typhimurium delayed and attenuated acidification of its intracellular compartment. Phagosomes containing S. typhimurium required 4-5 hr to reach pH < 5.0. In contrast, within 1 hr vacuoles containing heat-killed bacteria were measured at pH < 4.5. The eventual acidification of phagosomes to pH < 5.0 correlated with the period of maximal PhoP-dependent gene expression. These observations implicate phagosome acidification as an intracellular inducer of PhoP-regulated gene expression and suggest that Salmonella survival is dependent on its ability to attenuate phagosome acidification.
鼠伤寒沙门氏菌在巨噬细胞吞噬小体内的存活需要细菌基因产物的协同表达。本报告研究了吞噬体pH作为鼠伤寒沙门氏菌毒力调节因子PhoP和PhoQ正向调控基因表达信号的作用。小鼠骨髓来源的巨噬细胞吞噬细菌数小时后，PhoP激活的基因转录增加了50至77倍。相比之下，感染培养的上皮细胞后，未观察到PhoP激活的基因表达有差异，这表明膜传感器PhoQ识别巨噬细胞吞噬体特有的信号。当巨噬细胞培养基中含有NH4Cl或氯喹（可提高酸性区室pH的弱碱）时，PhoP调控的基因表达增加被消除。pH测量表明，鼠伤寒沙门氏菌延迟并减弱了其细胞内区室的酸化。含有鼠伤寒沙门氏菌的吞噬体需要4至5小时才能达到pH < 5.0。相比之下，含有热灭活细菌的液泡在1小时内pH就降至< 4.5。吞噬体最终酸化至pH < 5.0与PhoP依赖性基因表达的高峰期相关。这些观察结果表明吞噬体酸化是PhoP调控基因表达的细胞内诱导因子，并表明沙门氏菌的存活取决于其减弱吞噬体酸化的能力。
