Abstract
Bacterial outer membrane vesicle (OMV) is a kind of spherical lipid bilayer nanostructure naturally secreted by bacteria, which has diverse functions such as intracellular and extracellular communication, horizontal gene transfer, transfer of contents to host cells, and eliciting an immune response in host cells. In this review, several methods including ultracentrifugation and precipitation for isolating OMVs were summarized. The latest progresses of OMVs in biomedical fields, especially in vaccine development, cancer treatment, infection control, and bioimaging and detection were also summarized in this review. We highlighted the importance of genetic engineering for the safe and effective application and in facilitating the rapid development of OMVs. Finally, we discussed the bottleneck problems about OMVs in preparation and application at present and put forward our own suggestions about them. Some perspectives of OMVs in biomedical field were also provided.
Highlights
Living organisms tend to secrete factors such as proteins, molecules, polysaccharides, and other substances directly or indirectly to sustain their physiological activities (Brown et al 2015; Schwechheimer and Kuehn2015)
outer membrane vesicle (OMV) obtained from Escherichia coli (E. coli) was first reported in the 1960s, but the existent OMV produced by Gram-positive bacteria (Bacillus subtilis and Bacillus cereus) was first mentioned in literature in 1990, which may be caused by the different structure of cell wall between Gram-negative and Gram-positive bacteria (Bishop and Work 1965; Dorward and Garon 1990)
The saturation of the salt solution may increase after the precipitation, which was proven by Oishi et al When OMVs are collected, the saturation of salt solution increases from 40% to 75%, indicating that there are some free extracellular proteins released from bacteria that may non- bind to the salt (Oishi et al 2010)
Summary
Living organisms tend to secrete factors such as proteins, molecules, polysaccharides, and other substances directly or indirectly to sustain their physiological activities Based on the phenomenon that knockout or repression of VacJ/Yrb, two genes associated with phospholipid transporter, will increase OMV production in some Gram-negative bacteria, the forth model is proposed (Roier et al 2016) In this model, phospholipid will accumulate in the outer leaflet of the outer membrane when vacJ and/or yrb genes are silenced or deleted, which results in an asymmetric expansion of the outer leaflet and subsequently promotes an outward bulging of the outer membrane. The enrichment of positive and negative curvature induced by phospholipids facilitates the budding of the outer membrane, which pinches off to form an OMV (Fig. 2) This model can act in concert with all other three OMV formational models proposed hereinbefore and can almost perfectly represent the mechanism of secretion of OMV by Gram-negative bacteria. This review will demonstrate some significant progresses of OMVs, especially the genetically modified OMVs, which have made in vaccine development, tumor treatment, bacterial infection, and biological detection in recent years
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