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The Chlamydia trachomatis parasitophorous vacuolar membrane is not passively permeable to low-molecular-weight
1Laboratory of Intracellular Parasites, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana 59840-2999, USA. rheinzen@uwyo.edu
Abstract:
Chlamydia trachomatis is an obligately intracellular bacterial parasite of eucaryotic cells that undergoes a biphasic life cycle within a parasitophorous vacuole (PV) called an inclusion. The parasitophorous vacuolar membrane (PVM) constitutes a barrier between the replicating bacteria and the nutrient-rich environment of the host cytoplasm. To determine whether the chlamydial PVM contains pores that allow passive diffusion of metabolites between the host cytoplasm and the PV, fluorescent tracer molecules were introduced directly into the cytoplasm of infected cells by transfection or microinjection. Fluorescence microscopy and laser scanning confocal microscopy were subsequently employed to determine whether equilibration of the fluorescent tracers between the cytoplasm and the PV occurred. No movement of tracer molecules as small as 520 Da from the cytoplasm to the PV was observed. These data suggest that the chlamydial PV is not passively permeable to small molecules through open channels in the PVM.
Insights
Chlamydia trachomatis, an intracellular bacterium, replicates within a vacuole. This study found no evidence of pores in the vacuole membrane allowing nutrient passage, suggesting a barrier to metabolite diffusion.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Chlamydia trachomatis is an obligate intracellular bacterium with a biphasic life cycle.
- It resides within a specialized vacuole (inclusion) inside host cells.
- The vacuole membrane (PVM) separates the bacteria from the host cytoplasm.
Purpose of the Study:
- To investigate whether the chlamydial vacuole membrane (PVM) contains pores.
- To determine if small molecules can passively diffuse between the host cytoplasm and the chlamydial vacuole.
Main Methods:
- Introduction of fluorescent tracer molecules (up to 520 Da) into the cytoplasm of infected host cells via transfection or microinjection.
- Analysis using fluorescence and laser scanning confocal microscopy to detect tracer movement.
Main Results:
- No diffusion of fluorescent tracer molecules from the host cytoplasm into the chlamydial vacuole was observed.
- The PVM did not permit passive permeability to small molecules.
Conclusions:
- The chlamydial vacuole membrane acts as a barrier, preventing passive diffusion of small metabolites.
- The PVM is not perforated by open channels allowing nutrient exchange with the host cytoplasm.