-Containing Vacuoles Capture PtdIns(4)-Rich Vesicles Derived from the Golgi Apparatus.

is the causative agent of a pneumonia termed Legionnaires' disease. The facultative intracellular bacterium employs the Icm/Dot type IV secretion system (T4SS) and a plethora of translocated "effector" proteins to interfere with host vesicle trafficking pathways and establish a replicative niche, the -containing vacuole (LCV). Internalization of the pathogen and the events immediately ensuing are accompanied by host cell-mediated phosphoinositide (PI) lipid changes and the Icm/Dot-controlled conversion of the LCV from a PtdIns(3)-positive vacuole into a PtdIns(4)-positive replication-permissive compartment, which tightly associates with the endoplasmic reticulum. The source and formation of PtdIns(4) are ill-defined. Using dually labeled amoebae and real-time high-resolution confocal laser scanning microscopy (CLSM), we show here that nascent LCVs continuously capture and accumulate PtdIns(4)-positive vesicles from the host cell. Trafficking of these PtdIns(4)-positive vesicles to LCVs occurs independently of the Icm/Dot system, but their sustained association requires a functional T4SS. During the infection, PtdIns(3)-positive membranes become compacted and segregated from the LCV, and PtdIns(3)-positive vesicles traffic to the LCV but do not fuse. Moreover, using eukaryotic and prokaryotic PtdIns(4) probes (2×PH-green fluorescent protein [2×PH-GFP] and P4C-GFP, respectively) along with Arf1-GFP, we show that PtdIns(4)-rich membranes of the -Golgi network associate with the LCV. Intriguingly, the interaction dynamics of 2×PH-GFP and P4C-GFP are spatially separable and reveal the specific PtdIns(4) pool from which the LCV PI originates. These findings provide high-resolution real-time insights into how exploits the cellular dynamics of membrane-bound PtdIns(4) for LCV formation. The environmental bacterium causes a life-threatening pneumonia termed Legionnaires' disease. The bacteria grow intracellularly in free-living amoebae as well as in respiratory tract macrophages. To this end, forms a distinct membrane-bound compartment called the -containing vacuole (LCV). Phosphoinositide (PI) lipids are crucial regulators of the identity and dynamics of host cell organelles. The PI lipid PtdIns(4) is a hallmark of the host cell secretory pathway, and decoration of LCVs with this PI is required for pathogen vacuole maturation. The source, dynamics, and mode of accumulation of PtdIns(4) on LCVs are largely unknown. Using amoebae producing different fluorescent probes as host cells, we show here that LCVs rapidly acquire PtdIns(4) through the continuous interaction with PtdIns(4)-positive host vesicles derived from the Golgi apparatus. Thus, the PI lipid pattern of the secretory pathway contributes to the formation of the replication-permissive pathogen compartment.