Related Experiment Videos
Association of Legionella pneumophila with the macrophage endoplasmic reticulum
1Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
Abstract:
Legionella pneumophila replicates within a membrane-bounded compartment that is studded with ribosomes. In this study we investigated whether these ribosomes originate from the cytoplasmic pool or are associated with host endoplasmic reticulum (ER). Immunofluorescence and electron microscopic localization studies of ER proteins in macrophages infected with L. pneumophila indicated that the bacteria reside in a compartment surrounded by ER. An L. pneumophila mutant that grows slowly in macrophages was slow to associate with host ER, providing genetic evidence in support of the hypothesis that this specialized vacuole is required for intracellular bacterial growth. Ultrastructural studies, in which the ER luminal protein BiP was labeled by immunoperoxidase cytochemistry, revealed that L. pneumophila replication vacuoles resemble nascent autophagosomes. Furthermore, short-term amino acid starvation of macrophages, which stimulated host autophagosomes. Furthermore, short-term amino acid starvation of macrophages, which stimulated host autophagy, increased association of the bacteria with the ER and enhanced bacterial growth. These results are compatible with the hypothesis that L. pneumophila exploits the autophagy machinery of macrophages to establish an intracellular niche favorable for replication.
Insights
Legionella pneumophila bacteria utilize host endoplasmic reticulum (ER) to form a replication niche. This process involves the host
Area of Science:
- Cell Biology
- Microbiology
- Immunology
Background:
- Legionella pneumophila (L. pneumophila) is an intracellular bacterial pathogen that replicates within host cells.
- The replication vacuole of L. pneumophila is known to be associated with host cell organelles, but its precise origin and composition remain under investigation.
- Understanding the host-pathogen interaction at the organelle level is crucial for developing targeted therapeutic strategies.
Purpose of the Study:
- To determine whether ribosomes associated with the L. pneumophila replication vacuole originate from the host's cytoplasmic pool or endoplasmic reticulum (ER).
- To investigate the role of host ER in the formation of the L. pneumophila replication vacuole and its impact on bacterial growth.
- To explore the potential involvement of host autophagy pathways in L. pneumophila intracellular replication.
Main Methods:
- Immunofluorescence and electron microscopy were used to localize ER proteins in L. pneumophila-infected macrophages.
- L. pneumophila mutants with impaired intracellular growth were analyzed for their association with host ER.
- Ultrastructural studies using immunoperoxidase cytochemistry for the ER luminal protein BiP were performed.
- Macrophage autophagy was modulated by amino acid starvation to assess its effect on bacterial association with ER and growth.
Main Results:
- Immunofluorescence and electron microscopy revealed that L. pneumophila resides within a compartment surrounded by host ER.
- A slow-growing L. pneumophila mutant exhibited delayed association with host ER, suggesting ER association is critical for growth.
- Replication vacuoles resembled nascent autophagosomes, and enhanced host autophagy (induced by starvation) increased ER association and bacterial growth.
Conclusions:
- L. pneumophila actively recruits host ER to form its intracellular replication vacuole.
- The ER-associated vacuole, resembling a nascent autophagosome, is essential for efficient intracellular bacterial growth.
- L. pneumophila appears to hijack the host cell's autophagy machinery to create a favorable niche for replication.