A subscription to JoVE is required to view this content. Sign in or start your free trial.
Bacterial vesicles play important roles in pathogenesis and have promising biotechnological applications. The heterogeneity of vesicles complicates analysis and use; therefore, a simple, reproducible method to separate varying sizes of vesicles is necessary. Here, we demonstrate the use of size exclusion chromatography to separate heterogeneous vesicles produced by Aggregatibacter actinomycetemcomitans.
The cell wall of Gram-negative bacteria consists of an inner (cytoplasmic) and outer membrane (OM), separated by a thin peptidoglycan layer. Throughout growth, the outer membrane can bleb to form spherical outer membrane vesicles (OMVs). These OMVs are involved in numerous cellular functions including cargo delivery to host cells and communication with bacterial cells. Recently, the therapeutic potential of OMVs has begun to be explored, including their use as vaccines and drug delivery vehicles. Although OMVs are derived from the OM, it has long been appreciated that the lipid and protein cargo of the OMV differs, often significantly, from that of the OM. More recently, evidence that bacteria can release multiple types of OMVs has been discovered, and evidence exists that size can impact the mechanism of their uptake by host cells. However, studies in this area are limited by difficulties in efficiently separating the heterogeneously sized OMVs. Density gradient centrifugation (DGC) has traditionally been used for this purpose; however, this technique is time-consuming and difficult to scale-up. Size exclusion chromatography (SEC), on the other hand, is less cumbersome and lends itself to the necessary future scale-up for therapeutic use of OMVs. Here, we describe a SEC approach that enables reproducible separation of heterogeneously sized vesicles, using as a test case, OMVs produced by Aggregatibacter actinomycetemcomitans, which range in diameter from less than 150 nm to greater than 350 nm. We demonstrate separation of "large" (350 nm) OMVs and "small" (<150 nm) OMVs, verified by dynamic light scattering (DLS). We recommend SEC-based techniques over DGC-based techniques for separation of heterogeneously sized vesicles due to its ease of use, reproducibility (including user-to-user), and possibility for scale-up.
Gram-negative bacteria release vesicles derived from their outer membrane, so-called outer membrane vesicles (OMVs), throughout growth. These OMVs play important roles in cell-to-cell communication, both between bacteria and host as well as between bacterial cells, by carrying a number of important biomolecules, including DNA/RNA, proteins, lipids, and peptidoglycans1,2. In particular, the role of OMVs in bacterial pathogenesis has been extensively studied due to their enrichment in certain virulence factors and toxins3,4,5,6,7,8,9,10,11.
OMVs have been reported to range in size from 20 to 450 nm, depending on the parent bacteria and the growth stage, with several types of bacteria releasing heterogeneously sized OMVs8,12,13,14, which also differ in their protein composition and mechanism of host cell entry12. H. pylori released OMVs ranging in diameter from 20 to 450 nm, with the smaller OMVs containing a more homogeneous protein composition than the larger OMVs. Importantly, the two populations of OMVs were observed to be internalized by host cells via different mechanisms12. In addition, we have demonstrated that Aggregatibacter actinomycetemcomitans releases a population of small (<150 nm) OMVs along with a population of large (>350 nm) OMVs, with the OMVs containing a significant amount of a secreted protein toxin, leukotoxin (LtxA)15. While the role of OMV heterogeneity in cellular processes is clearly important, technical difficulties in separating and analyzing distinct populations of vesicles has limited these studies.
In addition to their importance in bacterial pathogenesis, OMVs have been proposed for use in a number of biotechnological applications, including as vaccines and drug delivery vehicles16,17,18,19,20. For their translational use in such approaches, a clean and monodisperse preparation of vesicles is required. Thus, effective and efficient methods of separation are necessary.
Most commonly, density gradient centrifugation (DGC) is used to separate heterogeneously sized vesicle populations from cellular debris, including flagellae and secreted proteins21; the method has also been reported as an approach to separate heterogeneously sized OMV subpopulations12,13,14. However, DGC is time-consuming, inefficient, and highly variable user-to-user22 and is, therefore, not ideal for scale-up. In contrast, size exclusion chromatography (SEC) represents a scalable, efficient, and consistent approach to purify OMVs21,23,24. We have found that a long (50-cm), gravity-flow, SEC column, filled with gel filtration medium is sufficient for efficiently purifying and separating subpopulations of OMVs. Specifically, we used this approach to separate A. actinomycetemcomitans OMVs into "large" and "small" subpopulations, as well as to remove protein and DNA contamination. Purification was completed in less than 4 h, and complete separation of the OMV subpopulations and removal of debris was accomplished.
1. Preparation of buffers
2. Preparation of OMV sample
3. Packing the S-1000 column
4. Loading the sample and collecting fractions
5. Sample analysis
A schematic of the protocol is shown in Figure 1.
Figure 1: Schematic of SEC procedure. The column is packed with degassed gel filtration medium carefully to avoid bubbles and discontinuities, then washed with two column volumes of elution buffer. Next, the sample is carefully pipetted onto the top of the gel, without disrupting gel packing. The column is opened and run until the sample completely enters the gel. At this point, buffer is placed on the top of the column, and the first 20 mL of eluate is collected. Next, a series of 1-mL fractions is collected. These fractions are then placed in a 96-well plate or 96-well immuno-plate for analysis of lipid and protein content. Please click here to view a larger version of this figure.
Figure 2 shows representative results from this method. OMVs produced by A. actinomycetemcomitans strain JP2 were first purified from the culture supernatant using ultracentrifugation15. We previously found that this strain produces two populations of OMVs, one with diameters of about 300 nm and one with diameters of about 100 nm15. To separate these OMV populations, we purified the sample using the SEC protocol described above. E...
Here, we have provided a protocol for the simple, fast, and reproducible separation of bacterial OMV subpopulations. Although the technique is relatively straight-forward, there are some steps that must be performed extremely carefully to ensure that efficient separation occurs in the column. First, it is essential that the gel be loaded into the column carefully and slowly to avoid air bubbles. We have observed that leaving the gel at room temperature for several hours before loading the column allows the gel to equilib...
The authors have no conflicts of interest to report.
This work was funded by the National Science Foundation (1554417) and National Institutes of Health (DE027769).
Name | Company | Catalog Number | Comments |
1-Step Ultra TMB-ELISA | Thermo Scientific | 34028 | |
Amicon 50 kDa filters | Millipore Sigma | UFC905024 | |
Bovine Serum Albumin (BSA) | Fisher Scientific | BP9704-100 | |
ELISA Immuno Plates | Thermo Scientific | 442404 | |
FM 4-64 | Thermo Scientific | T13320 | 1.5 x 50 cm |
Glass Econo-Column | BioRad | 7371552 | |
Infinite 200 Pro Plate Reader | Tecan | ||
Potassium Chloride (KCl) | Amresco (VWR) | 0395-500G | |
Potassium Phosphate Monobasic Anhydrous (KH2PO4) | Amresco (VWR) | 0781-500G | |
Sephacryl S-1000 Superfine | GE Healthcare | 17-0476-01 | |
Sodium Chloride (NaCl) | Fisher Chemical | S271-3 | |
Sodium Phosphate Dibasic Anhydrous (Na2HPO4) | Amresco (VWR) | 0404-500G | |
Tris Base | VWR | 0497-1KG | |
Tween(R) 20 | Acros Organics | 23336-2500 |
Request permission to reuse the text or figures of this JoVE article
Request PermissionThis article has been published
Video Coming Soon
Copyright © 2025 MyJoVE Corporation. All rights reserved