This work was funded by the National Science Foundation (1554417) and National Institutes of Health (DE027769).

1. Preparation of buffers
<ol>
	<li>To prepare the ELISA wash buffer, add 3.94 g Tris-base, 8.77 g NaCl, and 1 g bovine serum albumin (BSA) to 1 L of deionized (DI) water. Add 500 &#181;L polysorbate-20. Adjust the pH to 7.2 using HCl or NaOH.</li>
	<li>To prepare the blocking buffer, add 3.94 g Tris-base, 8.77 g NaCl, and 10 g BSA. Add 500 &#181;L polysorbate-20 to 1 L of DI water. Adjust the pH to 7.2 using HCl or NaOH.</li>
	<li>To prepare the elution buffer (PBS), add 8.01 g NaCl, 2.7 g KCl, 1.42 g Na2HPO4, and 0.24 g KH2PO4 to 1 L DI water. Adjust the pH to 7.4 using HCl or NaOH. 
	&#8203;NOTE: A 10x solution of this buffer can be made and diluted with DI water as needed.</li>
</ol>
2. Preparation of OMV sample
<ol>
	<li>Grow A. actinomycetemcomitans cells to the late exponential phase (optical density at 600 nm of 0.7). Pellet the cells by centrifuging twice at 10,000 x g at 4 &#176;C for 10 min. Filter the supernatant through a 0.45 &#181;m filter.</li>
	<li>Concentrate the bacteria-free supernatant using 50 kDa-molecular weight cut-off filters. Ultracentrifuge the concentrated solution at 105,000 x g at 4 &#176;C for 30 min.&#160;</li>
	<li>Resuspend the pellet in PBS and ultracentrifuge again (105,000 x g at 4 &#176;C for 30 min.) Resuspend the pellet in 2 mL of PBS.</li>
</ol>
3. Packing the S-1000 column
<ol>
	<li>Mix the stock bottle of gel filtration medium with a glass stir rod and pour out into a glass bottle the volume necessary to fill the column, plus approximately 50% excess (about 135 mL). Let these beads sit until they have settled, and then decant off the excess liquid. Resuspend the beads in elution buffer, so that the final solution is approximately 70% (by volume) gel, 30% buffer. Degas the solution under vacuum.</li>
	<li>Mount the glass column vertically using a ring stand and fill with elution buffer to wet the walls of the column. Drain the buffer until there is only about 1 cm of buffer remaining in the column.</li>
	<li>Without creating bubbles, carefully pipette beads into the column, filling the column to the top. Continue to drain excess buffer throughout this process. Be sure to not let the beads settle completely before adding additional beads to the top of the column. The column should be packed to a height of about 2 cm below the bottom of the column reservoir.</li>
</ol>
4. Loading the sample and collecting fractions
<ol>
	<li>Degas the elution buffer under vacuum. Wash the column with two column-volumes (180 mL) of elution buffer.</li>
	<li>Allow the remaining buffer to fully enter the column. Once the buffer has reached the top of the gel layer, carefully pipette a 2-mL sample containing OMVs (at a lipid concentration of approximately 100 - 200 nmol/L) onto the surface of the beads, being careful not to disturb any of the beads at the top of the column. Allow the sample to fully enter the gel, that is, when no liquid remains above the gel layer.&#160;</li>
	<li>Carefully and slowly add elution buffer on top of the gel column. Do not disturb the top layer of the gel, as this will cause sample dilution.</li>
	<li>Place a single 50-mL tube under the column and open the column. Collect the first 20 mL of the eluent. Add additional elution buffer to the top of the column, carefully, as needed to ensure the column is never dry.</li>
	<li>Place a series of 1.5 mL tubes under the column. Start the column and collect a series of 1-mL samples in each tube. As the samples are being collected, continue to add elution buffer to the top of the column, as necessary. Repeat until 96 fractions have been collected. Stop the column. 
	NOTE: The samples should be stored at -20 &#176;C for long-term storage or 4 &#176;C for short-term storage until further analysis.</li>
	<li>To clean the column, run one column volume (90 mL) of 0.1 M NaOH through the column. Run two column volumes (180 mL) of elution buffer through the column.</li>
</ol>
5. Sample analysis
<ol>
	<li>To measure the lipid concentration in each fraction, pipette 50 &#181;L of each fraction into a single well of a 96-well plate. To each well, add 2.5 &#181;L of lipophilic dye. Incubate for 15 s. Measure the fluorescence intensity on a plate reader with an excitation wavelength of 515 nm and an emission wavelength of 640 nm. To calculate the fraction of all lipid in each sample, sum all of the emission intensities and divide each individual intensity by the total.</li>
	<li>To measure the concentration of a particular protein, pipette 100 &#181;L of each fraction into a single well of an ELISA immuno-plate. Incubate at 25 &#176;C for 3 h.
	<ol>
		<li>Decant the samples. Add 200 &#181;L of ELISA wash buffer to each well and decant. Repeat four times for a total of five washes.</li>
		<li>Add 200 &#181;L of blocking buffer to each well and incubate for 1 h at 25 &#176;C. Decant.</li>
		<li>Incubate plates with 100 &#181;L blocking buffer plus primary antibody (1:10,000 for purified antibody; 1:10 for unpurified antibody) overnight at 4 &#176;C. Decant.</li>
		<li>Add 200 &#181;L of ELISA wash buffer to each well and decant. Repeat four times for a total of five washes.</li>
		<li>Add 100 &#181;L of ELISA wash buffer plus secondary antibody (1:30,000) to each well. Incubate for 1 h at 25 &#176;C.</li>
		<li>Add 200 &#181;L of ELISA wash buffer to each well and decant. Repeat four times for a total of five washes.</li>
		<li>Add 100 &#181;L of the 3,3&#39;,5,5&#39;-tetramethylbenzidine (TMB) one-step solution and incubate for 15-30 min or until a blue color develops. Stop the TMB reaction with 50 &#181;L of the stopping solution.</li>
		<li>On a plate reader, read the absorbance of each well at a wavelength of 450 nm.</li>
	</ol>
	</li>
	<li>To measure the total protein concentration, record the absorbance at a wavelength of 280 nm (A280) of each fraction, using a UV-vis spectrophotometer.</li>
</ol>
A schematic of the protocol is shown in Figure 1.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62429/62429fig01.jpg" /> 
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. <a href="https://www.jove.com/files/ftp_upload/62429/62429fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<ol>
	<li>Kuehn, M. J., Kesty, N. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bacterial+outer+membrane+vesicles+and+the+host-pathogen+interaction.">Bacterial outer membrane vesicles and the host-pathogen interaction.</a> Genes and Development. 19, 2645-2655 (2005).</li><li>Kulp, A., Kuehn, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+functions+and+biogenesis+of+secreted+bacterial+outer+membrane+vesicles.">Biological functions and biogenesis of secreted bacterial outer membrane vesicles.</a> Annual Reviews Microbiology. 64, 163-184 (2010).</li><li>Kato, S., Kowashi, Y., Demuth, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Outer+membrane-like+vesicles+secreted+by+Actinobacillus+actinomycetemcomitans+are+enriched+in+leukotoxin.">Outer membrane-like vesicles secreted by Actinobacillus actinomycetemcomitans are enriched in leukotoxin.</a> Microbial Pathogenesis. 32 (1), 1-13 (2002).</li><li>Nice, J. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aggregatibacter+actinomycetemcomitans+leukotoxin+is+delivered+to+host+cells+in+an+LFA-1-independent+manner+when+associated+with+outer+membrane+vesicles.">Aggregatibacter actinomycetemcomitans leukotoxin is delivered to host cells in an LFA-1-independent manner when associated with outer membrane vesicles.</a> Toxins. 10 (10), 414 (2018).</li><li>Haurat, M. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+sorting+of+cargo+proteins+into+bacterial+membrane+vesicles.">Selective sorting of cargo proteins into bacterial membrane vesicles.</a> Journal of Biological Chemistry. 286 (2), 1269-1276 (2011).</li><li>Horstman, A. L., Kuehn, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enterotoxigenic+Escherichia+coli+secretes+active+heat-labile+enterotoxin+via+outer+membrane+vesicles.">Enterotoxigenic Escherichia coli secretes active heat-labile enterotoxin via outer membrane vesicles.</a> The Journal of Biological Chemistry. 275 (17), 12489-12496 (2000).</li><li>Wai, S. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vesicle-mediated+export+and+assembly+of+pore-forming+oligomers+of+the+Enterobacterial+ClyA+cytotoxin.">Vesicle-mediated export and assembly of pore-forming oligomers of the Enterobacterial ClyA cytotoxin.</a> Cell. 115, 25-35 (2003).</li><li>Balsalobre, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Release+of+the+Type+I+secreted+&#945;-haemolysin+via+outer+membrane+vesicles+from+Escherichia+coli.">Release of the Type I secreted &#945;-haemolysin via outer membrane vesicles from Escherichia coli.</a> Molecular Microbiology. 59 (1), 99-112 (2006).</li><li>Donato, G. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Delivery+of+Bordetella+pertussis+adenylate+cyclase+toxin+to+target+cells+via+outer+membrane+vesicles.">Delivery of Bordetella pertussis adenylate cyclase toxin to target cells via outer membrane vesicles.</a> FEBS Letters. 586, 459-465 (2012).</li><li>Kim, Y. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Outer+membrane+vesicles+of+Vibrio+vulnificus+deliver+cytolysin-hemolysin+VvhA+into+epithelial+cells+to+induce+cytotoxicity.">Outer membrane vesicles of Vibrio vulnificus deliver cytolysin-hemolysin VvhA into epithelial cells to induce cytotoxicity.</a> Biochemical and Biophysical Research Communications. 399, 607-612 (2010).</li><li>Maldonado, R., Wei, R., Kachlany, S. C., Kazi, M., Balashova, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cytotoxic+effects+of+Kingella+kingae+outer+membrane+vesicles+on+human+cells.">Cytotoxic effects of Kingella kingae outer membrane vesicles on human cells.</a> Microbial Pathogenesis. 51 (1-2), 22-30 (2011).</li><li>Turner, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Helicobacter+pylori+outer+membrane+vesicle+size+determines+their+mechanisms+of+host+cell+entry+and+protein+content.">Helicobacter pylori outer membrane vesicle size determines their mechanisms of host cell entry and protein content.</a> Frontiers in Immunology. 9, 1466 (2018).</li><li>Zavan, L., Bitto, N. J., Johnston, E. L., Greening, D. W., Kaparakis-Liaskos, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Helicobacter+pylori+growth+stage+determines+the+size,+protein+composition,+and+preferential+cargo+packaging+of+outer+membrane+vesicles.">Helicobacter pylori growth stage determines the size, protein composition, and preferential cargo packaging of outer membrane vesicles.</a> Proteomics. 19 (1-2), 1800209 (2019).</li><li>Rompikuntal, P. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Perinuclear+localization+of+internalized+outer+membrane+vesicles+carrying+active+cytolethal+distending+toxin+from+Aggregatibacter+actinomycetemcomitans.">Perinuclear localization of internalized outer membrane vesicles carrying active cytolethal distending toxin from Aggregatibacter actinomycetemcomitans.</a> Infections and Immunity. 80 (1), 31-42 (2012).</li><li>Nice, J. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aggregatibacter+actinomycetemcomitans+leukotoxin+is+delivered+to+host+cells+in+an+LFA-1-independent+manner+when+associated+with+outer+membrane+vesicles.">Aggregatibacter actinomycetemcomitans leukotoxin is delivered to host cells in an LFA-1-independent manner when associated with outer membrane vesicles.</a> Toxins. 10 (10), 414 (2018).</li><li>Stevenson, T. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunization+with+outer+membrane+vesicles+displaying+conserved+surface+polysaccharide+antigen+elicits+broadly+antimicrobial+antibodies.">Immunization with outer membrane vesicles displaying conserved surface polysaccharide antigen elicits broadly antimicrobial antibodies.</a> Proceedings of the National Academy of Sciences. 115 (14), 3106-3115 (2018).</li><li>Gujrati, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bioengineered+bacterial+outer+membrane+vesicles+as+cell-specific+drug-delivery+vehicles+for+cancer+therapy.">Bioengineered bacterial outer membrane vesicles as cell-specific drug-delivery vehicles for cancer therapy.</a> ACS Nano. 8 (2), 1525-1537 (2014).</li><li>Huang, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+novel+nanoantibiotics+using+an+outer+membrane+vesicle-based+drug+efflux+mechanism.">Development of novel nanoantibiotics using an outer membrane vesicle-based drug efflux mechanism.</a> Journal of Controlled Release. 317, 1-22 (2020).</li><li>Chen, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Delivery+of+foreign+antigens+by+engineered+outer+membrane+vesicle+vaccines.">Delivery of foreign antigens by engineered outer membrane vesicle vaccines.</a> Proceedings of the National Academy of Sciences. 107 (7), 3099-3104 (2010).</li><li>Chen, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Outer+membrane+vesicles+displaying+engineered+glycotopes+elicit+protective+antibodies.">Outer membrane vesicles displaying engineered glycotopes elicit protective antibodies.</a> Proceedings of the National Academy of Sciences. 113 (26), 3609-3618 (2016).</li><li>Singorenko, P. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+membrane+vesicles+from+prokaryotes:+A+technical+and+biological+comparison+reveals+heterogeneity.">Isolation of membrane vesicles from prokaryotes: A technical and biological comparison reveals heterogeneity.</a> Journal of Extracellular Vesicles. 6 (1), 1324731 (2017).</li><li>Zeringer, E., Barta, T., Li, M., Vlassov, A. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strategies+for+isolation+of+exosomes.">Strategies for isolation of exosomes.</a> Cold Spring Harbor Protocols. 2015 (4), 319-323 (2015).</li><li>Benedikter, B. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafiltration+combined+with+size+exclusion+chromatography+efficiently+isolates+extracellular+vesicles+from+cell+culture+media+for+compositional+and+functional+studies.">Ultrafiltration combined with size exclusion chromatography efficiently isolates extracellular vesicles from cell culture media for compositional and functional studies.</a> Science Reports. 7 (1), 15297 (2017).</li><li>Mol, E. A., Goumans, M. J., Doevendans, P. A., Sluijter, J. P. G., Vader, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Higher+functionality+of+extracellular+vesicles+isolated+using+size-exclusion+chromatography+compared+to+ultracentrifugation.">Higher functionality of extracellular vesicles isolated using size-exclusion chromatography compared to ultracentrifugation.</a> Nanomedicine. 13 (6), 2061-2065 (2017).</li><li>Lally, E. T., Golub, E. E., Kieba, I. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+immunological+characterization+of+the+domain+of+Actinobacillus+actinomycetemcomitans+leukotoxin+that+determines+its+specificity+for+human+target+cells.">Identification and immunological characterization of the domain of Actinobacillus actinomycetemcomitans leukotoxin that determines its specificity for human target cells.</a> Journal of Biological Chemistry. 269 (49), 31289-31295 (1994).</li><li>Chang, E. H., Giaquinto, P., Huang, J., Balashova, N. V., Brown, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epigallocatechin+gallate+inhibits+leukotoxin+release+by+Aggregatibacter+actinomycetemcomitans+by+promoting+association+with+the+bacterial+membrane.">Epigallocatechin gallate inhibits leukotoxin release by Aggregatibacter actinomycetemcomitans by promoting association with the bacterial membrane.</a> Molecular Oral Microbiology. 35 (1), 29-39 (2020).</li><li>Klimentov&#225;, J., Stul&#237;k, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+of+isolation+and+purification+of+outer+membrane+vesicles+from+gram-negative+bacteria.">Methods of isolation and purification of outer membrane vesicles from gram-negative bacteria.</a> Microbiological Research. 170, 1-9 (2015).</li><li>Dauros Singorenko, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+membrane+vesicles+from+prokaryotes:+a+technical+and+biological+comparison+reveals+heterogeneity.">Isolation of membrane vesicles from prokaryotes: a technical and biological comparison reveals heterogeneity.</a> Journal of Extracellular Vesicles. 6 (1), 1324731 (2017).</li><li>Mongui&#243;-Tortajada, M., G&#225;lvez-Mont&#243;n, C., Bayes-Genis, A., Roura, S., Borr&#224;s, F. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extracellular+vesicle+isolation+methods:+rising+impact+of+size-exclusion+chromatography.">Extracellular vesicle isolation methods: rising impact of size-exclusion chromatography.</a> Cellular and Molecular Life Sciences. 76 (12), 2369-2382 (2019).</li></ol>

The authors have no conflicts of interest to report.

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...

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 (&#60;150 nm) OMVs along with a population of large (&#62;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&#160;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 &#34;large&#34; and &#34;small&#34; 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.

<table><tbody><tr><td>1-Step Ultra TMB-ELISA</td><td>Thermo Scientific</td><td>34028</td><td></td></tr><tr><td>Amicon 50 kDa filters</td><td>Millipore Sigma</td><td>UFC905024</td><td></td></tr><tr><td>Bovine Serum Albumin (BSA)</td><td>Fisher Scientific</td><td>BP9704-100</td><td></td></tr><tr><td>ELISA Immuno Plates</td><td>Thermo Scientific</td><td>442404</td><td></td></tr><tr><td>FM 4-64</td><td>Thermo Scientific</td><td>T13320</td><td>1.5 x 50 cm</td></tr><tr><td>Glass Econo-Column</td><td>BioRad</td><td>7371552</td><td></td></tr><tr><td>Infinite 200 Pro Plate Reader</td><td>Tecan</td><td></td><td></td></tr><tr><td>Potassium Chloride (KCl)</td><td>Amresco (VWR)</td><td>0395-500G</td><td></td></tr><tr><td>Potassium Phosphate Monobasic Anhydrous (KH&lt;sub&gt;2&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt;)</td><td>Amresco (VWR)</td><td>0781-500G</td><td></td></tr><tr><td>Sephacryl S-1000 Superfine</td><td>GE Healthcare</td><td>17-0476-01</td><td></td></tr><tr><td>Sodium Chloride (NaCl)</td><td>Fisher Chemical</td><td>S271-3</td><td></td></tr><tr><td>Sodium Phosphate Dibasic Anhydrous (Na&lt;sub&gt;2&lt;/sub&gt;HPO&lt;sub&gt;4&lt;/sub&gt;)</td><td>Amresco (VWR)</td><td>0404-500G</td><td></td></tr><tr><td>Tris Base</td><td>VWR</td><td>0497-1KG</td><td></td></tr><tr><td>Tween&lt;sup&gt;(R)&lt;/sup&gt; 20</td><td>Acros Organics</td><td>23336-2500</td><td></td></tr></tbody></table>

size exclusion chromatography to analyze bacterial outer membrane vesicle heterogeneity

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 &#34;large&#34; (350 nm) OMVs and &#34;small&#34; (&#60;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.

Figure 2&#160;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...

Watch this Scientific Journal Video about Size Exclusion Chromatography to Analyze Bacterial Outer Membrane Vesicle Heterogeneity at JoVE.com

Size Exclusion Chromatography to Analyze Bacterial Outer Membrane Vesicle Heterogeneity

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 ...

size-exclusion-chromatography-to-analyze-bacterial-outer-membrane

Research

JoVE Journal

Bioengineering

4.3K Views.  Lehigh University. 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.

Video: Size Exclusion Chromatography to Analyze Bacterial Outer Membrane Vesicle Heterogeneity

Isolating Small Extracellular Vesicles and Extracting Their Peptidome

Identification of Peptides of Small Extracellular Vesicles from Bone Marrow-Derived Macrophages

Small extracellular vesicles (sEVs) are typically secreted by the exocytosis of multivesicular bodies (MVBs). These nanovesicles with a diameter of &lt;200 nm are present in various body fluids. These sEVs regulate various biological processes such as gene transcription and translation, cell proliferation and survival, immunity and inflammation through their cargos, such as proteins, DNA, RNA, and metabolites. Currently, various techniques have been developed for sEVs isolation. Among them, the ultracentrifugation-based method is considered the gold standard and is widely used for sEVs isolation. The peptides are naturally biomacromolecules with less than 50 amino acids in length. These peptides participate in a variety of biological processes with biological activity, such as hormones, neurotransmitters, and cell growth factors. The peptidome is intended to systematically analyze endogenous peptides in specific biological samples by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Here, we introduced a protocol to isolate sEVs by differential ultracentrifugation and extracted peptidome for identification by LC-MS/MS. This method identified hundreds of sEVs-derived peptides from bone marrow-derived macrophages.

Author Spotlight: Peptidome Extraction from Small Extracellular Vesicles Isolated from Bone Marrow-Derived Macrophages 

This protocol describes a procedure to isolate small extracellular vesicles from macrophages by differential ultracentrifugation and extract the peptidome for identification by mass spectrometry.

Small extracellular vesicles (sEVs) are typically secreted by the exocytosis of multivesicular bodies (MVBs). These nanovesicles with a diameter of ...

Biochemistry

Isolation and Characterization of Extracellular Vesicles Produced by Iron-limited Mycobacteria

Mycobacteria, including Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis, naturally release extracellular vesicles (EVs) containing immunologically active molecules. Knowledge regarding the molecular mechanisms of vesicle biogenesis, the content of the vesicles, and their functions at the pathogen-host interface is very limited. Addressing these questions requires rigorous procedures for isolation, purification, and validation of EVs. Previously, vesicle production was found to be enhanced when M. tuberculosis was exposed to iron restriction, a condition encountered by Mtb in the host environment. Presented here is a complete and detailed protocol to isolate and purify EVs from iron-deficient mycobacteria. Quantitative and qualitative methods are applied to validate purified EVs.

Mycobacterium tuberculosis shows increased production and release of extracellular vesicles in response to low iron conditions. This work details a protocol for generating low iron conditions and methods for the purification and characterization of mycobacterial extracellular vesicles released in response to iron deficiency.

Mycobacteria, including Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis, naturally release extracellular vesicles (EVs) ...

Immunology and Infection

Separation of the Cell Envelope for Gram-negative Bacteria into Inner and Outer Membrane Fractions with Technical Adjustments for Acinetobacter baumannii

This method works by partitioning the envelope of Gram-negative bacteria into total, inner, and outer membrane (OM) fractions and concludes with assays to assess the purity of the bilayers. The OM has an increased overall density compared to the inner membrane, largely due to the presence of lipooligosaccharides (LOS) and lipopolysaccharides (LPS) within the outer leaflet. LOS and LPS molecules are amphipathic glycolipids that have a similar structure, which consists of a lipid-A disaccharolipid and core-oligosaccharide substituent. However, only LPS molecules are decorated with a third subunit known as the O-polysaccharide, or O-antigen. The type and amount of glycolipids present will impact an organism&#8217;s OM density. Therefore, we tested whether the membranes of bacteria with varied glycolipid content could be similarly isolated using our technique. For the LPS-producing organisms, Salmonella enterica serovar Typhimurium and Escherichia coli, the membranes were easily isolated and the LPS O-antigen moiety did not impact bilayer partitioning. Acinetobacter baumannii produces LOS molecules, which have a similar mass to O-antigen deficient LPS molecules; however, the membranes of these microbes could not initially be separated. We reasoned that the OM of A. baumannii was less dense than that of Enterobacteriaceae, so the sucrose gradient was adjusted and the membranes were isolated. The technique can therefore be adapted and modified for use with other organisms.

Separation of the Cell Envelope for Gram-negative Bacteria into Inner and Outer Membrane Fractions with Technical Adjustments for Acinetobacter baumannii

Gram-negative bacteria produce two spatially segregated membranes. The outer membrane is partitioned from the inner membrane by a periplasm and a peptidoglycan layer. The ability to isolate the dual bilayers of these microbes has been critical for understanding their physiology and pathogenesis.

This method works by partitioning the envelope of Gram-negative bacteria into total, inner, and outer membrane (OM) fractions and concludes with assays to ...

Mycobacterium tuberculosis Extracellular Vesicle Enrichment through Size Exclusion Chromatography

The role of extracellular vesicles (EVs) in the context of bacterial infection has emerged as a new avenue for understanding microbial physiology. Specifically, Mycobacterium tuberculosis (Mtb) EVs play a role in the host-pathogen interaction and response to environmental stress. Mtb EVs are also highly antigenic and show potential as vaccine components. The most common method for purifying Mtb EVs is density gradient ultracentrifugation. This process has several limitations, including low throughput, low yield, reliance on expensive equipment, technical challenges, and it can negatively impact the resulting preparation. Size exclusion chromatography (SEC) is a gentler alternative method that combats many of the limitations of ultracentrifugation. This protocol demonstrates that SEC is effective for Mtb EV enrichment and produces high-quality Mtb EV preparations of increased yield in a rapid and scalable manner. Additionally, a comparison to density gradient ultracentrifugation by quantification and qualification procedures demonstrates the benefits of SEC. While the evaluation of EV quantity (nanoparticle tracking analysis), phenotype (transmission electron microscopy), and content (Western blotting) is tailored to Mtb EVs, the workflow provided can be applied to other mycobacteria.

Mycobacterium tuberculosis Extracellular Vesicle Enrichment through Size Exclusion Chromatography

This protocol describes size exclusion chromatography, a facile and reproducible technique for enriching Mycobacterium tuberculosis extracellular vesicles from culture supernatants.

The role of extracellular vesicles (EVs) in the context of bacterial infection has emerged as a new avenue for understanding microbial physiology. ...

Size Exclusion Chromatography for Separating Extracellular Vesicles from Conditioned Cell Culture Media

Extracellular vesicles (EVs) are nano-sized lipid-membrane bound structures that are released from all cells, are present in all biofluids, and contain proteins, nucleic acids, and lipids that are reflective of the parent cell from which they are derived. Proper separation of EVs from other components in a sample allows for characterization of their associated cargo and lends insight into their potential as intercellular communicators and non-invasive biomarkers for numerous diseases. In the current study, oligodendrocyte derived EVs were isolated from cell culture media using a combination of state-of-the-art techniques, including ultrafiltration and size exclusion chromatography (SEC) to separate EVs from other extracellular proteins and protein complexes. Using commercially available SEC columns, EVs were separated from extracellular proteins released from human oligodendroglioma cells under both control and endoplasmic reticulum (ER) stress conditions. The canonical EV markers CD9, CD63, and CD81 were observed in fractions 1-4, but not in fractions 5-8. GM130, a protein of the Golgi apparatus, and calnexin, an integral protein of the ER, were used as negative EV markers, and were not observed in any fraction. Further, when pooling and concentrating fractions 1-4 as the EV fraction, and fractions 5-8 as the protein fraction, expression of CD63, CD81, and CD9 in the EV fraction was observed. The expression of GM130 or calnexin was not observed in either of the fraction types. The pooled fractions from both control and ER stress conditions were visualized with transmission electron microscopy and vesicles were observed in the EV fractions, but not in the protein fractions. Particles in the EV and protein fractions from both conditions were also quantified with nanoparticle tracking analysis. Together, these data demonstrate that SEC is an effective method for separating EVs from conditioned cell culture media.

The protocol here demonstrates that extracellular vesicles can be adequately separated from conditioned cell culture media using size exclusion chromatography.

Extracellular vesicles (EVs) are nano-sized lipid-membrane bound structures that are released from all cells, are present in all biofluids, and contain ...

Neuroscience

Isolation and Characterization of Microvesicles from Peripheral Blood

The release of extracellular vesicles (EVs) including small endosomal-derived exosomes (Exos, diameter &#60; 100 nm) and large plasma membrane-derived microvesicles (MVs, diameter &#62; 100 nm) is a fundamental cellular process that occurs in all living cells. These vesicles transport proteins, lipids and nucleic acids specific for their cell of origin and in vitro studies have highlighted their importance as mediators of intercellular communication. EVs have been successfully isolated from various body fluids and especially EVs in blood have been identified as promising biomarkers for cancer or infectious diseases. In order to allow the study of MV subpopulations in blood, we present a protocol for the standardized isolation and characterization of MVs from peripheral blood samples. MVs are pelleted from EDTA-anticoagulated plasma samples by differential centrifugation and typically possess a diameter of 100 - 600 nm. Due to their larger size, they can easily be studied by flow cytometry, a technique that is routinely used in clinical diagnostics and available in most laboratories. Several examples for quality control assays of the isolated MVs will be given and markers that can be used for the discrimination of different MV subpopulations in blood will be presented.

Extracellular vesicles present in blood have been suggested as novel biomarkers for various diseases. Here, we present a protocol for the isolation of large plasma membrane-derived microvesicles from peripheral blood samples and their subsequent analysis by conventional flow cytometry and Western Blotting.

The release of extracellular vesicles (EVs) including small endosomal-derived exosomes (Exos, diameter &#60; 100 nm) and large plasma membrane-derived ...

Biology

Scalable Isolation and Purification of Extracellular Vesicles from Escherichia coli and Other Bacteria

Diverse bacterial species secrete ~20-300 nm extracellular vesicles (EVs), comprised of lipids, proteins, nucleic acids, glycans, and other molecules derived from the parental cells. EVs function as intra- and inter-species communication vectors while also contributing to the interaction between bacteria and host organisms in the context of infection and colonization. Given the multitude of functions attributed to EVs in health and disease, there is a growing interest in isolating EVs for in vitro and in vivo studies. It was hypothesized that the separation of EVs based on physical properties, namely size, would facilitate the isolation of vesicles from diverse bacterial cultures. 
The isolation workflow consists of centrifugation, filtration, ultrafiltration, and size-exclusion chromatography (SEC) for the isolation of EVs from bacterial cultures. A pump-driven tangential flow filtration (TFF) step was incorporated to enhance scalability, enabling the isolation of material from liters of starting cell culture. Escherichia coli was used as a model system expressing EV-associated nanoluciferase and non-EV-associated mCherry as reporter proteins. The nanoluciferase was targeted to the EVs by fusing its N-terminus with cytolysin A. Early chromatography fractions containing 20-100 nm EVs with associated cytolysin A - nanoLuc were distinct from the later fractions containing the free proteins. The presence of EV-associated nanoluciferase was confirmed by immunogold labeling and transmission electron microscopy. This EV isolation workflow is applicable to other human gut-associated gram-negative and gram-positive bacterial species. In conclusion, combining centrifugation, filtration, ultrafiltration/TFF, and SEC enables scalable isolation of EVs from diverse bacterial species. Employing a standardized isolation workflow will facilitate comparative studies of microbial EVs across species.

Scalable Isolation and Purification of Extracellular Vesicles from Escherichia coli and Other Bacteria

Bacteria secrete nanometer-sized extracellular vesicles (EVs) carrying bioactive biological molecules. EV research focuses on understanding their biogenesis, role in microbe-microbe and host-microbe interactions and disease, as well as their potential therapeutic applications. A workflow for scalable isolation of EVs from various bacteria is presented to facilitate standardization of EV research.

Diverse bacterial species secrete ~20-300 nm extracellular vesicles (EVs), comprised of lipids, proteins, nucleic acids, glycans, and other molecules ...

Isolation and Characterization of Cyanobacterial Extracellular Vesicles

Cyanobacteria are a diverse group of photosynthetic, Gram-negative bacteria that play critical roles in global ecosystems and serve as essential biotechnology models. Recent work has demonstrated that both marine and freshwater cyanobacteria produce extracellular vesicles -&#160;small membrane-bound structures released from the outer surface of the microbes. While vesicles likely contribute to diverse biological processes, their specific functional roles in cyanobacterial biology remain largely unknown. To encourage and advance research in this area, a detailed protocol is presented for isolating, concentrating, and purifying cyanobacterial extracellular vesicles. The current work discusses methodologies that have successfully isolated vesicles from large cultures of Prochlorococcus, Synechococcus, and Synechocystis. Methods for quantifying and characterizing vesicle samples from these strains are presented. Approaches for isolating vesicles from aquatic field samples are also described. Finally, typical challenges encountered with cyanobacterial vesicle purification, methodological considerations for different downstream applications, and the trade-offs between approaches are also discussed.

The present protocol providesdetailed descriptions for isolation, concentration,and characterization of extracellular vesicles from cyanobacterial cultures. Approaches for purifying vesicles from cultures at different scales, trade-offs among methodologies, and considerations for working with field samples are also discussed.

Cyanobacteria are a diverse group of photosynthetic, Gram-negative bacteria that play critical roles in global ecosystems and serve as essential ...

Enhanced Bacterial Extracellular Vesicles Isolation for Microbiota Multi-Omics

Isolation and Purification of Bacterial Extracellular Vesicles from Human Feces Using Density Gradient Centrifugation

Bacterial extracellular vesicles (BEVs) are nanovesicles derived from bacteria that play an active role in bacteria-bacteria and bacteria-host communication, transferring bioactive molecules such as proteins, lipids, and nucleic acids inherited from the parent bacteria. BEVs derived from the gut microbiota have effects within the gastrointestinal tract and can reach distant organs, resulting in significant implications for physiology and pathology. Theoretical investigations that explore the types, quantities, and roles of BEVs derived from human feces are crucial for understanding the secretion and function of BEVs from the gut microbiota. These investigations also necessitate an improvement in the current strategy for isolating and purifying BEVs.
This study optimized the isolation and purification process of BEVs by establishing two density gradient centrifugation (DGC) modes: Top-down and Bottom-up. The enriched distribution of BEVs was determined in fractions 6 to 8 (F6-F8). The effectiveness of the approach was evaluated based on particle morphology, size, concentration, and protein content. The particle and protein recovery rates were calculated, and the presence of specific markers was analyzed to compare the recovery and purity of the two DGC modes. The results indicated that the Top-down centrifugation mode had lower contamination levels and achieved a recovery rate and purity similar to that of the Bottom-up mode. A centrifugation time of 7 h was sufficient to achieve a fecal BEV concentration of 108/mg.
Apart from feces, this method could be applied to other body fluid types with proper modification according to the differences in components and viscosity. In conclusion, this detailed and reliable protocol would facilitate the standardized isolation and purification of BEVs and thus, lay a foundation for subsequent multi-omics analysis and functional experiments.

Author Spotlight: Accelerating Research on Bacterial Extracellular Vesicles Separation and Heterogeneity 

This study describes a method to isolate and purify bacterial extracellular vesicles (BEVs) enriched from human feces via density gradient centrifugation (DGC), identifies the physical characteristics of BEVs from morphology, particle size, and concentration, and discusses the potential applications of the DGC approach in clinical and scientific research.

Bacterial extracellular vesicles (BEVs) are nanovesicles derived from bacteria that play an active role in bacteria-bacteria and bacteria-host ...

Size Exclusion Chromatography Based Separation of Bacterial Extracellular Vesicles: A Technique to Separate Heterogenous Population of Gram-Negative Bacterial Outer Membrane Vesicles Based on Their Size

Source: Collins, S. M., et al., <a href="https://www.jove.com/v/62429">Size Exclusion Chromatography to Analyze Bacterial Outer Membrane Vesicle Heterogeneity</a>. J. Vis. Exp. (2021).
In this video, we demonstrate a technique&#8211;size exclusion chromatography&#8211;to separate a heterogenous population of outer membrane vesicles or OMVs derived from bacteria. These vesicles are nanosized spherical structures and are separated into large and small subpopulations based on their size through Size Exclusion Chromatography.

Source: Collins, S. M., et al., Size Exclusion Chromatography to Analyze Bacterial Outer Membrane Vesicle Heterogeneity. J. Vis. Exp. (2021).
In this ...

Size Exclusion Chromatography to Analyze Bacterial Outer Membrane Vesicle Heterogeneity

Summary

Explore More Videos

Chapters in this video

Identification of Peptides of Small Extracellular Vesicles from Bone Marrow-Derived Macrophages

Isolation and Characterization of Extracellular Vesicles Produced by Iron-limited Mycobacteria

Separation of the Cell Envelope for Gram-negative Bacteria into Inner and Outer Membrane Fractions with Technical Adjustments for Acinetobacter baumannii

Mycobacterium tuberculosis Extracellular Vesicle Enrichment through Size Exclusion Chromatography

Size Exclusion Chromatography for Separating Extracellular Vesicles from Conditioned Cell Culture Media

Isolation and Characterization of Microvesicles from Peripheral Blood

Scalable Isolation and Purification of Extracellular Vesicles from Escherichia coli and Other Bacteria

Isolation and Characterization of Cyanobacterial Extracellular Vesicles

Isolation and Purification of Bacterial Extracellular Vesicles from Human Feces Using Density Gradient Centrifugation

Size Exclusion Chromatography Based Separation of Bacterial Extracellular Vesicles: A Technique to Separate Heterogenous Population of Gram-Negative Bacterial Outer Membrane Vesicles Based on Their Size