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Published on: July 22, 2011
Secretion of Salmonella Pathogenicity Island 1-Encoded Type III Secretion System Effectors by Outer Membrane Vesicles
Seul I Kim1, Seongok Kim1, Eunsuk Kim1
1Department of Molecular Science and Technology, Ajou University, Suwon, South Korea.
Abstract:
Outer membrane vesicles (OMVs) are spherical membranous structures released by Gram-negative bacteria. Several bacterial pathogens utilize OMVs as vehicles for the delivery of virulence factors into host cells. Results of our previous study on proteomic analysis revealed that OMVs isolated from Salmonella enterica serovar Typhimurium had virulence effectors that are known to be translocated by Salmonella pathogenicity island 1 (SPI-1)-encoded type III secretion system (T3SS1) into the host cell. In the present study, immunoblot analysis confirmed the secretion of the six T3SS1 effector proteins, namely SipB and SipC (translocators of T3SS1), and SipA, SopA, SopB, and SopE2 (effectors translocated by T3SS1), by OMVs. Results of proteinase K treatment revealed the localization of these T3SS1 effector proteins on the outer surface of OMVs. SipC and SopE2 were secreted by OMVs independent of the three secretion systems T3SS1, T3SS2, and flagella, signifying OMVs to be an alternative delivery system to T3SSs. T3SS1 effectors SipA, SipC, and SopE2 were internalized into the cytoplasm of the host cell by OMVs independent of cellular Salmonella-host cell contact. In epithelial cells, addition of OMVs harboring T3SS1 effectors stimulated the production of F-actin, thereby complementing the attenuated invasion of ΔsopE2 into host cells. These results suggest that S. Typhimurium might exploit OMVs as a long-distance vehicle to deliver T3SS1 effectors into the cytoplasm of the host cell independent of bacteria-host cell interaction.
Insights
Salmonella Typhimurium outer membrane vesicles (OMVs) deliver type III secretion system 1 (T3SS1) effectors to host cells. These OMVs act as an alternative delivery system, independent of bacterial contact, to enhance host cell invasion.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Cell Biology
Background:
- Gram-negative bacteria release outer membrane vesicles (OMVs) that can deliver virulence factors.
- Salmonella Typhimurium utilizes the Salmonella pathogenicity island 1 (SPI-1)-encoded type III secretion system 1 (T3SS1) to translocate effectors into host cells.
- Previous studies indicated OMVs from S. Typhimurium contain T3SS1 effectors.
Purpose of the Study:
- To confirm the presence and localization of T3SS1 effector proteins in S. Typhimurium OMVs.
- To investigate the secretion mechanism and host cell delivery function of OMVs carrying T3SS1 effectors.
- To explore OMVs as an alternative delivery system for bacterial virulence factors.
Main Methods:
- Immunoblot analysis to detect T3SS1 effector proteins (SipB, SipC, SipA, SopA, SopB, SopE2) in OMVs.
- Proteinase K treatment to determine the surface localization of effector proteins on OMVs.
- Cell culture experiments using epithelial cells to assess OMV-mediated effector internalization and host cell actin rearrangement.
Main Results:
- Immunoblotting confirmed the presence of six T3SS1 effector proteins on the surface of S. Typhimurium OMVs.
- Secretion of SipC and SopE2 by OMVs occurred independently of T3SS1, T3SS2, and flagellar systems.
- OMVs delivered T3SS1 effectors SipA, SipC, and SopE2 into host cell cytoplasm without direct bacterial contact, stimulating F-actin production and complementing invasion defects.
Conclusions:
- S. Typhimurium utilizes OMVs as an alternative secretion pathway to deliver T3SS1 effectors into host cells.
- OMV-mediated effector delivery is independent of bacterial-host cell contact, suggesting a 'long-distance' virulence mechanism.
- OMVs represent a significant virulence factor, contributing to host cell manipulation and invasion.
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