Offense and defense: microbial membrane vesicles play both ways

Macdonald, Ian A.; Kuehn, Meta J.

doi:10.1016/j.resmic.2012.10.020

Cited by 151 publications

(151 citation statements)

References 123 publications

Supporting

Mentioning

147

Contrasting

Unclassified

Order By: Relevance

“…Based on these findings, we hypothesized that the P. aeruginosa PA14-derived exoproteome competes with bacterial binding to NETs. Prior studies revealed that P. aeruginosa spontaneously, or under stress, produces OMVs (29). When comparing the recently identified P. aeruginosa PA14 OMV proteome (30) to the NETassociated proteome, 81 proteins were shared (Fig.…”

Section: Resultsmentioning

confidence: 92%

Distinct Susceptibilities of Corneal Pseudomonas aeruginosa Clinical Isolates to Neutrophil Extracellular Trap-Mediated Immunity

et al. 2014

View full text Add to dashboard Cite

Ocular bacterial keratitis, often associated with Pseudomonas aeruginosa bacterial infection, commonly occurs in contact lens wearers and may lead to vision impairment. In this study, we analyzed the contribution of neutrophil extracellular traps (NETs) to the mediation of protection during ocular keratitis. Both invasive and cytotoxic P. aeruginosa clinical isolates induced NET release by neutrophils. NETs carried the characteristic histone proteins, elastase, lysozyme, myeloperoxidase, and metabolic enzymes. While the invasive P. aeruginosa strains PAO1 (serogroup O5) and 6294 (serogroup O6) were trapped by NETs, the cytotoxic P. aeruginosa strains 6077, 6206 (serogroup O11), and PA14 (serogroup 010) were less sensitive to NET capture. The mechanism of escape by the cytotoxic strains from adhesion to NETs involved the shedding of outer membrane vesicles (OMVs) that outcompeted the cytotoxic P. aeruginosa strains for NET binding. When ocular infection was caused by an invasive strain in vivo, NETs were released at the ocular surface to capture bacteria, limiting their spread. Treatment with MNase I had a dose-dependent effect, with low doses of MNase speeding up bacterial clearance and high doses of MNase having toxic consequences. Cumulatively, our data suggest that NET-mediated immunity is a two-step process. Initially, pathogens attach to NET fragments; subsequently, upon nuclease activity, active serine proteases, which proteolytically degrade NET-associated proteins and promote DNase activity, are released. Therefore, a balance between NET production and NET degradation is needed to achieve maximal NET immunity. Infections caused by Pseudomonas aeruginosa are frequently associated with bacterial ocular keratitis, a condition that carries the risk of vision impairment and occurs in contact lens wearers or after ocular trauma. The majority of bacterial clinical isolates derived from corneal ulcers arising during keratitis can be divided into two functionally distinct groups: invasive and cytotoxic isolates. These two groups have distinct phenotypes; the cytotoxic strains cause rapid cell lysis, whereas the invasive strains replicate in the target cells (1, 2). These differences translate into various severities of disease; in mouse keratitis studies where infection is induced by cytotoxic strains, disease pathology is worse than that caused by invasive strains (3). Consistent with these findings, patients infected with cytotoxic strains have experienced more severe pathology and, consequently, suffered from greater visual impairment after recovery from infection (4). The immune response to both invasive and cytotoxic strains is dominated by dense neutrophil infiltrates, yet the infiltration pattern and responses of polymorphonuclear neutrophils (PMNs) differ depending on the type of strain. Due to the recently described ability of neutrophils to release DNA in the form of neutrophil extracellular traps (NETs) (5) and the presence of extracellular DNA during cytotoxic infections, we questioned whether the cyt...

show abstract

Section: Resultsmentioning

confidence: 92%

Distinct Susceptibilities of Corneal Pseudomonas aeruginosa Clinical Isolates to Neutrophil Extracellular Trap-Mediated Immunity

et al. 2014

View full text Add to dashboard Cite

show abstract

“…OMV cargo proteins are protected against degradation and can be transported over long distances in a concentrated manner (57,60). While OMVs from animal-pathogenic bacteria presumably fuse with the host cell membrane to deliver virulence factors (61), the access of OMVs from plant pathogens to the host cell membrane is presumably hindered by the plant cell wall. To date, OMVs from plant-pathogenic bacteria have only been reported for X. campestris pv.…”

Section: Discussionmentioning

confidence: 99%

Xanthomonas campestris pv. vesicatoria Secretes Proteases and Xylanases via the Xps Type II Secretion System and Outer Membrane Vesicles

et al. 2015

View full text Add to dashboard Cite

Many plant-pathogenic bacteria utilize type II secretion (T2S) systems to secrete degradative enzymes into the extracellular milieu. T2S substrates presumably mediate the degradation of plant cell wall components during the host-pathogen interaction and thus promote bacterial virulence. Previously, the Xps-T2S system from Xanthomonas campestris pv. vesicatoria was shown to contribute to extracellular protease activity and the secretion of a virulence-associated xylanase. The identities and functions of additional T2S substrates from X. campestris pv. vesicatoria, however, are still unknown. In the present study, the analysis of 25 candidate proteins from X. campestris pv. vesicatoria led to the identification of two type II secreted predicted xylanases, a putative protease and a lipase which was previously identified as a virulence factor of X. campestris pv. vesicatoria. Studies with mutant strains revealed that the identified xylanases and the protease contribute to virulence and in planta growth of X. campestris pv. vesicatoria. When analyzed in the related pathogen X. campestris pv. campestris, several T2S substrates from X. campestris pv. vesicatoria were secreted independently of the T2S systems, presumably because of differences in the T2S substrate specificities of the two pathogens. Furthermore, in X. campestris pv. vesicatoria T2S mutants, secretion of T2S substrates was not completely absent, suggesting the contribution of additional transport systems to protein secretion. In line with this hypothesis, T2S substrates were detected in outer membrane vesicles, which were frequently observed for X. campestris pv. vesicatoria. We, therefore, propose that extracellular virulence-associated enzymes from X. campestris pv. vesicatoria are targeted to the Xps-T2S system and to outer membrane vesicles. IMPORTANCEThe virulence of plant-pathogenic bacteria often depends on TS2 systems, which secrete degradative enzymes into the extracellular milieu. T2S substrates are being studied in several plant-pathogenic bacteria, including Xanthomonas campestris pv. vesicatoria, which causes bacterial spot disease in tomato and pepper. Here, we show that the T2S system from X. campestris pv. vesicatoria secretes virulence-associated xylanases, a predicted protease, and a lipase. Secretion assays with the related pathogen X. campestris pv. campestris revealed important differences in the T2S substrate specificities of the two pathogens. Furthermore, electron microscopy showed that T2S substrates from X. campestris pv. vesicatoria are targeted to outer membrane vesicles (OMVs). Our results, therefore, suggest that OMVs provide an alternative transport route for type II secreted extracellular enzymes. Many Gram-negative plant-pathogenic bacteria utilize specialized protein secretion systems to deliver virulence factors, including DNA or bacterial effector proteins, into plant cells (1). The efficient trans-kingdom transport of bacterial effector proteins is often hindered by the rigid plant cell wall, which mainly cons...

show abstract

“…E xtracellular vesicles are produced by all branches of microbial life (1). Most thoroughly studied in Gram-negative bacteria, the functions of these vesicles ranges from disposal of waste products and misfolded proteins to secretion of quorum-sensing signals to delivery of virulence-associated molecules (2). In the fungal kingdom, extracellular vesicles were first described in Cryptococcus neoformans and have subsequently been discovered in a variety of basidio-and ascomycetes (3)(4)(5).…”

mentioning

confidence: 99%

Interaction of Cryptococcus neoformans Extracellular Vesicles with the Cell Wall

et al. 2014

View full text Add to dashboard Cite

bCryptococcus neoformans produces extracellular vesicles containing a variety of cargo, including virulence factors. To become extracellular, these vesicles not only must be released from the plasma membrane but also must pass through the dense matrix of the cell wall. The greatest unknown in the area of fungal vesicles is the mechanism by which these vesicles are released to the extracellular space given the presence of the fungal cell wall. Here we used electron microscopy techniques to image the interactions of vesicles with the cell wall. Our goal was to define the ultrastructural morphology of the process to gain insights into the mechanisms involved. We describe single and multiple vesicle-leaving events, which we hypothesized were due to plasma membrane and multivesicular body vesicle origins, respectively. We further utilized melanized cells to "trap" vesicles and visualize those passing through the cell wall. Vesicle size differed depending on whether vesicles left the cytoplasm in single versus multiple release events. Furthermore, we analyzed different vesicle populations for vesicle dimensions and protein composition. Proteomic analysis tripled the number of proteins known to be associated with vesicles. Despite separation of vesicles into batches differing in size, we did not identify major differences in protein composition. In summary, our results indicate that vesicles are generated by more than one mechanism, that vesicles exit the cell by traversing the cell wall, and that vesicle populations exist as a continuum with regard to size and protein composition.

show abstract

Offense and defense: microbial membrane vesicles play both ways

Cited by 151 publications

References 123 publications

Distinct Susceptibilities of Corneal Pseudomonas aeruginosa Clinical Isolates to Neutrophil Extracellular Trap-Mediated Immunity

Distinct Susceptibilities of Corneal Pseudomonas aeruginosa Clinical Isolates to Neutrophil Extracellular Trap-Mediated Immunity

Xanthomonas campestris pv. vesicatoria Secretes Proteases and Xylanases via the Xps Type II Secretion System and Outer Membrane Vesicles

Interaction of Cryptococcus neoformans Extracellular Vesicles with the Cell Wall

Contact Info

Product

Resources

About