Secretion of Salmonella Pathogenicity Island 1-Encoded Type III Secretion System Effectors by Outer Membrane Vesicles in Salmonella enterica Serovar Typhimurium

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.

Bacterial Actin-Specific Endoproteases Grimelysin and Protealysin as Virulence Factors Contributing to the Invasive Activities of Serratia

“…These interactions activate receptor-mediated cell signaling cascades and lead to bacterial uptake [2,4,60,61,86]. Recent data showed however that the virulence components transported via the type III secretion system of pathogenic bacteria can be also translocated into the eukaryotic cells by the bacterial outer membrane vesicles (OMVs) [87]. Importantly, OMVs can be produced by opportunistic bacteria as well as by pathogenic ones [88][89][90][91][92], thus smoothing the difference between pathogenic bacteria and facultative bacterial pathogens.…”

Intracellular Pathogens: Host Immunity and Microbial Persistence Strategies

“…Persistent bacterial pathogens have developed a secretion system to deliver virulence factors such as toxins and effectors interfering with apoptosis into the host cell, thereby enhancing intracellular survival. Out of seven such secretion systems, type III (T3SS) (used by Chlamydia trachomatis and Salmonella typhimurium) and type IV secretion systems (T4SS) (used by Legionella and Brucella ) are the most widely studied [192, 193, 239]. M. tuberculosis uses a specialized secretion system, Esx secretion systems (ESX-1, ESX-3, and ESX-5), to deliver major T cell antigens ESAT-6 and CFP-10 into the host [191].…”

The Serratia grimesii outer membrane vesicles‐associated grimelysin triggers bacterial invasion of eukaryotic cells

“…Outer membrane vesicles released from Gram‐negative bacteria may function as a vehicle in the delivery of virulence factors to host cells (Kim et al, 2018). As we have previously shown, Gram‐negative bacteria S. grimesii produce metalloprotease grimelysin characterized by a specific proteolytic activity toward actin (E. Bozhokina et al, 2008).…”

“…Specifically, OMVs have been found to deliver active toxins to host cells, including the enterotoxigenic Escherichia coli heat‐labile enterotoxin, the enterohemorrhagic E. coli pore‐forming cytotoxin cytolysin A, and the H. pylori VacA protein (Gankema, Wensink, Guinee, Jansen, & Witholt, 1980; Horstman and Kuehn 2000; Horstman & Kuehn 2002). It is also shown that OMVs isolated from Salmonella enterica translocate the virulence proteins known to be injected into host cells using a type III secretion system, thus being a long‐distance vehicle to deliver virulence effectors into the cytoplasm of the host cell independent of bacteria–host cell interaction (Kim, Kim, Kim, Hwang, & Yoon, 2018).…”