Name: assessing the viability of a synthetic bacterial consortium on the in vitro gut host-microbe interface
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The authors gratefully acknowledge financial support from the Flanders Research Foundation to Marta Calatayud Arroyo (FWO postdoctoral fellowship-12N2815N). Emma Hernandez-Sanabria is a postdoctoral fellow supported by Flanders Innovation and Entrepreneurship (Agentschap voor Innovatie door Wetenschap en Technologie, IWT).

1. Strains and Culture Conditions
NOTE: The synthetic oral community was composed by strains commonly present in the oral microbiome3.
<ol>
	<li>Obtain the following strains from the American Type Culture Collection (ATCC): Aggregatibacter actinomycetemcomitans (ATCC 43718), Fusobacterium nucleatum (ATCC 10953), Porphyromonas gingivalis (ATCC 33277), Prevotella intermedia (ATCC 25611), Streptococcus</e...

<ol>
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U., Egli, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+and+interpretation+of+bacterial+viability+by+using+the+LIVE/DEAD+BacLight+kit+in+combination+with+flow+cytometry.">Assessment and interpretation of bacterial viability by using the LIVE/DEAD BacLight kit in combination with flow cytometry.</a> Applied and Environmental Microbiology. 73, 3283-3290 (2007).</li><li>Props, R., Monsieurs, P., Mysara, M., Clement, L., Boon, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+the+biodiversity+of+microbial+communities+by+flow+cytometry.">Measuring the biodiversity of microbial communities by flow cytometry.</a> Methods in Ecology and Evolution. 7, 1376-1385 (2016).</li><li>Yamashita, Y., Takeshita, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+oral+microbiome+and+human+health.">The oral microbiome and human health.</a> Journal of Oral Science. 59, 201-206 (2017).</li><li>Wade, W. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+oral+microbiome+in+health+and+disease.">The oral microbiome in health and disease.</a> Pharmacological Research. 69, 137-143 (2013).</li><li>Yu, 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=A+resource+for+cell+line+authentication,+annotation+and+quality+control.">A resource for cell line authentication, annotation and quality control.</a> Nature. 520, 307 (2015).</li><li>Pelaseyed, T., 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=The+mucus+and+mucins+of+the+goblet+cells+and+enterocytes+provide+the+first+defense+line+of+the+gastrointestinal+tract+and+interact+with+the+immune+system.">The mucus and mucins of the goblet cells and enterocytes provide the first defense line of the gastrointestinal tract and interact with the immune system.</a> Immunological Reviews. 260, 8-20 (2014).</li><li>Bengoa, A. A., 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=Simulated+gastrointestinal+conditions+increase+adhesion+ability+of+Lactobacillus+paracasei+strains+isolated+from+kefir+to+Caco-2+cells+and+mucin.">Simulated gastrointestinal conditions increase adhesion ability of Lactobacillus paracasei strains isolated from kefir to Caco-2 cells and mucin.</a> Food Research International. 103, 462-467 (2018).</li><li>Kleiveland, C. R., et al., Verhoeckx, 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=.">.</a> The Impact of Food Bioactives on Health: in vitro and ex vivo models. , 197-205 (2015).</li><li>Laparra, J. 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The oral microbiome is a key element in human health as recently reported by several authors20,21. Previous findings suggest that the ingestion of saliva containing large loads of bacteria can influence the microbial ecosystem of the small intestine, which is one of the main sites for immune priming. The combination of a static upper gastrointestinal digestion model with the host interface represented by intestinal epithelial and mucus-secreting cells, served to ...

Humans cohabit with bacteria, which are present at the same number as human cells1. Hence, it is of crucial important to obtain a comprehensive understanding of the human microbiome. The oral cavity is a unique environment in that it is divided into several smaller habitats, thus containing a large variety of bacteria and biofilms in those different locations. Being an open ecosystem, some species in the mouth may be transient visitors. However, certain microorganisms colonize soon after birth and form organized biofilms2. These are found in the teeth surface above the gingival crevice, the subgingival crevice, tongue, mucosal surfaces and dental prosthetics and fillings3. Bacteria can also be present as flocs and planktonic cells in the lumen of the tooth canal, either intermixed with necrotic pulp tissue or suspended in a fluid phase.
There is active, continuous cross-talk between host cells and the resident microbiota4. Bacteria communicate within and between species, and only a small proportion of the natural colonizers can adhere to tissues, while other bacteria attach to these primary colonizers. For instance, cell-cell binding between microorganisms is key for integrating secondary colonizers into oral biofilms, and building complex networks of interacting microbial cells4. Around 70% of bacterial aggregates in a saliva sample are formed by Porphyromonas sp., Streptococcus sp., Prevotella sp., Veillonella sp., and unidentified Bacteroidetes. F. nucleatum is an intermediate colonizer in the subgingival biofilm and aggregates with the late colonizers P. gingivalis, T. denticola, and Tannerella forsythia, which are implicated in periodontitis5. In addition, Streptococcus mitis occupies both mucosal and dental habitats, while S. sanguinis and S. gordonii prefer to colonize teeth3. Thus, S. sanguinis is present in lower incisors and canines, while Actinomyces naeslundii has been found in upper anteriors6.
In addition, the indigenous microbiome plays a role in maintaining human health2. Resident microbiota participates in immune education and in preventing pathogen expansion. This colonisation resistance occurs because the native bacteria may be better adapted at attaching to surfaces, and more efficient at metabolising the available nutrients for growth. Although probiotic strains survive the gastrointestinal passage and remain active, the persistence of autochthonous bacteria swallowed from an upper location of the gastrointestinal tract has not been fully described. Thus, we subjected an artificial community, representative of the oral ecosystem, to simulated gastrointestinal transit conditions. Viability of bacterial cells was assessed using a multicompartment model resembling the gut epithelium. Current gut simulators offer suitable reproducibility in terms of analysis of the luminal microbial community7. However, bacterial adhesion and host-microbe interaction are separately addressed, as combining cell lines with microbial communities is challenging8. In contrast, we present a framework that provides potential mechanistic explanation of successful colonization events reported on the gut interface. Indeed, this model can be jointly used with a static gut model to evaluate the impact of microbial communities on host surface signalling.

<table>
	<tbody>
		<tr>
			<td>STRAINS</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Aggregatibacter actinomycetemcomitans </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 43718</td>
			<td></td>
		</tr>
		<tr>
			<td>Fusobacterium nucleatum </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 10953</td>
			<td></td>
		</tr>
		<tr>
			<td>Porphyromonas gingivalis </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 33277</td>
			<td></td>
		</tr>
		<tr>
			<td>Prevotella intermedia </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 25611</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus mutans </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 25175</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus sobrinus </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 33478</td>
			<td></td>
		</tr>
		<tr>
			<td>Actinomyces viscosus </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 15987</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus salivarius&#160; TOVE-R</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus mitis </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 49456</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus sanguinis </td>
			<td>BCCM/LMG Bacteria Collection</td>
			<td>LMG 14657</td>
			<td></td>
		</tr>
		<tr>
			<td>Veillonella parvula </td>
			<td>Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures</td>
			<td>DSM 2007</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus gordonii </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 49818</td>
			<td></td>
		</tr>
		<tr>
			<td>CELL LINES</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Caco-2 cells</td>
			<td>European Collection of Authenticated Cell Cultures</td>
			<td>86010202</td>
			<td></td>
		</tr>
		<tr>
			<td>HT29-MTX cells</td>
			<td>European Collection of Authenticated Cell Cultures</td>
			<td>12040401</td>
			<td></td>
		</tr>
		<tr>
			<td>REAGENTS AND CONSUMABLES</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Brain Heart Infusion (BHI) broth</td>
			<td>Oxoid</td>
			<td>CM1135</td>
			<td></td>
		</tr>
		<tr>
			<td>Blood Agar 2</td>
			<td>Oxoid</td>
			<td>CM0055</td>
			<td>Blood Agar medium</td>
		</tr>
		<tr>
			<td>Menadione</td>
			<td>Sigma</td>
			<td>M9429</td>
			<td></td>
		</tr>
		<tr>
			<td>Hemin</td>
			<td>Sigma</td>
			<td>H9039</td>
			<td></td>
		</tr>
		<tr>
			<td>5% sterile defibrinated horse blood</td>
			<td>E&#38;O Laboratories Ltd,</td>
			<td>P030</td>
			<td></td>
		</tr>
		<tr>
			<td>InnuPREP PCRpure Kit</td>
			<td>Analytik Jena</td>
			<td>845-KS-5010250</td>
			<td>PCR purification kit</td>
		</tr>
		<tr>
			<td>Big Dye</td>
			<td>Applied Biosystems</td>
			<td>4337454</td>
			<td>Dye for sequencing</td>
		</tr>
		<tr>
			<td>ABI Prism BigDye Terminator v3.1 cycle sequencing kit</td>
			<td>Applied Biosystems</td>
			<td>4337456</td>
			<td></td>
		</tr>
		<tr>
			<td>SYBR&#160;Green I</td>
			<td>Invitrogen</td>
			<td>S7585</td>
			<td></td>
		</tr>
		<tr>
			<td>Propidium Iodide</td>
			<td>Invitrogen</td>
			<td>P1304MP</td>
			<td></td>
		</tr>
		<tr>
			<td>T25 culture flasks uncoated, cell-culture treated, vented, sterile</td>
			<td>VWR</td>
			<td>734-2311</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA solution</td>
			<td>Sigma-Aldrich</td>
			<td>T3924-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan Blue solution 
			0.4%, liquid, sterile-filtered</td>
			<td>Sigma-Aldrich</td>
			<td>T8154&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Gibco</td>
			<td>14190250</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM cell culture media, with GlutaMAX and Pyruvate</td>
			<td>Life technologies</td>
			<td>31966-047</td>
			<td></td>
		</tr>
		<tr>
			<td>Corning Transwell polyester membrane cell culture inserts</td>
			<td>Sigma-Aldrich</td>
			<td>CLS3450-24EA</td>
			<td></td>
		</tr>
		<tr>
			<td>Mucin from porcine stomach Type II&#160;&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>M2378</td>
			<td></td>
		</tr>
		<tr>
			<td>Inactivated fetal bovine serum</td>
			<td>Greiner Bio One</td>
			<td>758093</td>
			<td></td>
		</tr>
		<tr>
			<td>Antibiotic-Antimycotic (100X)</td>
			<td>Gibco</td>
			<td>15240062</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X 100 for molecular biology</td>
			<td>Sigma-Aldrich</td>
			<td>T8787&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS without calcium, magnesium</td>
			<td>Gibco</td>
			<td>14190-250</td>
			<td></td>
		</tr>
		<tr>
			<td>Pierce LDH Cytotoxicity Assay Kit</td>
			<td>Thermo Fisher Scientific</td>
			<td>88953</td>
			<td></td>
		</tr>
		<tr>
			<td>Corning HTS Transwell-24 well, pore size 0.4 &#181;m</td>
			<td>Corning Costar Corp</td>
			<td>3450</td>
			<td></td>
		</tr>
		<tr>
			<td>Nuclease-free water</td>
			<td>Serva Electrophoresis</td>
			<td>28539010</td>
			<td></td>
		</tr>
		<tr>
			<td>EQUIPMENT</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Neubauer counting chamber improved</td>
			<td>Carl Roth</td>
			<td>T729.1</td>
			<td></td>
		</tr>
		<tr>
			<td>BD Accuri C6 Flow cytometer</td>
			<td>BD Biosciences</td>
			<td>653118</td>
			<td></td>
		</tr>
		<tr>
			<td>PowerLyzer 24 Homogenizer</td>
			<td>MoBio</td>
			<td>13155</td>
			<td></td>
		</tr>
		<tr>
			<td>T100 Thermal Cycler</td>
			<td>BioRad</td>
			<td>186-1096</td>
			<td></td>
		</tr>
		<tr>
			<td>Flush system</td>
			<td>Custom made</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>InnOva 4080 Incubator Shaker</td>
			<td>New Brunswick Scientific</td>
			<td>8261-30-1007</td>
			<td>Shaker for 2.10</td>
		</tr>
		<tr>
			<td>Memmert CO2 incubator</td>
			<td>Memmert GmbH &#38; Co.</td>
			<td>ICO150med</td>
			<td></td>
		</tr>
		<tr>
			<td>Millicell ERS (Electrical Resistance System)</td>
			<td>EMD Millipore, Merck KGaA</td>
			<td>MERS00002</td>
			<td></td>
		</tr>
		<tr>
			<td>Millipore Milli-Q academic, ultra pure water system</td>
			<td>Millipore, Merck KGaA</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>Shaker (ROCKER 3D basic)</td>
			<td>IKA</td>
			<td>4000000</td>
			<td>Shaker for 6.10</td>
		</tr>
	</tbody>
</table>

assessing the viability of a synthetic bacterial consortium on the in vitro gut host-microbe interface

The interplay between host and microbiota has been long recognized and extensively described. The mouth is similar to other sections of the gastrointestinal tract, as resident microbiota occurs and prevents colonisation by exogenous bacteria. Indeed, more than 600 species of bacteria are found in the oral cavity, and a single individual may carry around 100 different at any time. Oral bacteria possess the ability to adhere to the various niches in the oral ecosystem, thus becoming integrated within the resident microbial communities, and favouring growth and survival. However, the flow of bacteria into the gut during swallowing has been proposed to disturb the balance of the gut microbiota. In fact, oral administration of P. gingivalis shifted bacterial composition in the ileal microflora. We used a synthetic community as a simplified representation of the natural oral ecosystem, to elucidate the survival and viability of oral bacteria subjected to simulated gastrointestinal transit conditions. Fourteen species were selected, subjected to in vitro salivary, gastric, and intestinal digestion processes, and presented to a multicompartment cell model containing Caco-2 and HT29-MTX cells to simulate the gut mucosal epithelium. This model served to unravel the impact of swallowed bacteria on cells involved in the enterohepatic circulation. Using synthetic communities allows for controllability and reproducibility. Thus, this methodology can be adapted to assess pathogen viability and subsequent inflammation-associated changes, colonization capacity of probiotic mixtures, and ultimately, potential bacterial impact on the presystemic circulation.

This protocol leads to the generation of a model suitable for elucidating the survival and viability of oral bacteria subjected to simulated gastrointestinal transit conditions. The counts of intact cells from individual strains is approximately 108 cells mL-1 prior the creation of the synthetic community, while the multispecies microcosm contained above 90% of viable cells during the establishment of the community (Figure 1A </s...

Watch this Scientific Journal Video about Assessing the Viability of a Synthetic Bacterial Consortium on the In Vitro Gut Host-microbe Interface at JoVE.com

Assessing the Viability of a Synthetic Bacterial Consortium on the In Vitro Gut Host-microbe Interface

Gut host-microbe interactions were assessed using a novel approach combining a synthetic oral community, in vitro gastrointestinal digestion, and a model of the small intestine epithelium. We present a method that can be adapted to evaluate cell invasion of pathogens and multi-species biofilms, or even to test probiotic formulations&#39; survivability.

Assessing the Viability of a Synthetic Bacterial Consortium on the In Vitro Gut Host-microbe Interface

The interplay between host and microbiota has been long recognized and extensively described. The mouth is similar to other sections of the ...

This model is the next step in setting host microdirections for the upper digestive tracts. It is allowing addressing mechanistic research questions and it offers many opportunities for the food, the pharma, and nutraceutical industry and also toxicology. The main advantage of this technique is that it combines a model of the gastrointestinal system with the host micro interface including a complex microbe community.It is very applicable and it is very flexible as well. This methodology can be adopted using other cell types to assess pathogen viability and subsequent information. Changes can also be used to assist colonization capacity of probiotic mixtures and ultimately the potential effect of bacterias on the per systemic circulation.To begin, autoclave the medium, and then add five microgram per milliliter of hemen and one microgram per milliliter of menadione. Dispense nine milliliters of the medium into Hungate tubes, and close the tubes with a rubber stopper and an aluminum cap. Then flush the tubes with a mixture of 90%nitrogen and 10%carbon dioxide.Use the syringe to retrieve one milliliter of anaerobic medium, and transfer it to a 1.5 milliliter microcentrifuge tube. Pick single colonies of each bacterial species and resuspend them in the medium. Then transfer the colonies into the anaerobic modified BHI, and incubate them at 37 degrees celsius for 48 hours.Following the incubation, use filtered sterilized PBS to dilute the cultures to 10 to the fifth cells per milliliter. Then use flow cytometry with the cyber green propidium iodide stain to measure the cell number. Evaluating the microbiome community composition and viability is essential for avoiding bias in our experiment.Remove the cell culture medium from the flasks, then use five milliliters of PBS without calcium or magnesium to wash the cells once. Add two milliliters of trypsin EDTA solution to the cells. Distribute the solution by gently moving the flask.Then remove 1.5 milliliters of the trypsin solution, and incubate the flask at 37 degrees celsius for 10 minutes. After checking under the microscope if the cells have become detached, add five milliliters of supplemented cell culture medium to the flask to inactivate the trypsin, and pipette up and down to obtain a homogenous single cell suspension. Immediately mix a 50 microliter aliquot of the cell suspension with sterile 0.4%trypan blue solution in a 1:1 volume to volume proportion for KCO2 cells for a 1:5 volume to volume for HT29MTX.Mix by pipetting, and load the suspension into a counting chamber before counting the cells under the microscope. After preparing KCO2 and HT29MTX cell suspensions according to the text protocol, homogenize the suspensions, and add the corresponding volume of KCO2 and HT29MTX cells to a pre-filled sterile container with supplemented cell culture medium. Aspirate the pre-incubated medium from the apical side of the previously prepared chamber.Gently mix the cell suspension by pipetting, and transfer 1.5 milliliters to the apical compartment of the chamber inserts mixing the cell suspension every one to three wells to ensure constant homogenization. Gently move the plates back and forth and then right to left to evenly spread the cells in the well. Transfer the plates to the incubator, and repeat the movement of the plates.The sitting of the cells need to be done with constant homogenization of the cell suspension to ensure an even spread in the well. To measure the epithelial barrier integrity before starting the ASA, ensure that tier equipment is fully charged before starting the measurements. Disconnect the tier equipment from the power supply, and cover with a plastic autoclave bag.Make a hole in the bag to introduce the electrode into the input port on the meter. Then spray the bag with 70%ethanol before transferring the tier equipment into the flow cabinet. To disinfect the electrode, immerse the electrode tips in 70%ethanol for 15 minutes.Allow the tips to air dry for 15 seconds, then use cell culture medium to rinse the electrode. Allow the cells to come to room temperature inside the flow cabinet. Make sure that the meter is disconnected from the charger, then set the mode switch to Ohms, and turn on the power switch.Measure the cell resistance by immersing the electrode with the shorter tip in the insert and the longer tip out of the well. Keep the electrode at a 90 degree angle to the plate insert. To simulate oral digestion, transfer three milliliters of the bacterial community in a 50 milliliter sterile tube, and mix with three milliliters of simulated saliva fluid or SSF.Add 75 units per milliliter of alpha-amylase from human saliva type 9A and two grams per liter of mucin from porcine stomach type 2. Incubate the mixture at 37 degrees celsius and 100 RPM for two minutes. Collect a two milliliter sample for DNA extraction and flow cytometry quantification.To simulate gastric digestion, add four milliliters of simulated gastric fluid or SGF to three milliliters of the bacteria. Use one molar HCl to adjust the pH to three if necessary. Incubate the sample at 37 degrees celsius and 100 RPM for two minutes.Then collect a two milliliter sample. For small intestine digestions, add four milliliters simulated intestinal fluid or SIF to the bacteria. Use sodium hydroxide to adjust the pH if necessary.Then incubate the sample at 37 degrees celsius and 100 RPM for two minutes. And collect a two milliliter sample. After washing and adjusting the cell density of the small intestine digestion according to the text protocol, remove the apical medium from the transwell system, and add 1.5 milliliters of the bacterial suspension.Co-culture the system under general cell-culture conditions for two hours. Following incubation, measure the tier values to evaluate the integrity of the epithelial barrier as demonstrated earlier in the video. Add 0.5 milliliters of 10 millimolar n-acetylcysteine and HPSS to solubilize the mucus produced by the HT29MTX and to recover the adhered bacteria.Incubate the plates at 37 degrees celsius for one hour under agitation. Recover the NAC HPSS in a microcentrifuge tube, and use one milliliter of DPBS to wash the cells twice. Add 0.5 milliliters of 0.5%triton-x100 on top of the monolayers, and disrupt the cells by pipetting.Then quickly recover the liquid in vortex for one minute. Speed is crucial to avoid damaging the bacterial cells with the detergent. Analyze the samples according to the text protocol.As reported here, the counts of intact cells from individual strains were approximately 10 to the eighth cells per milliliter prior to the creation of the synthetic community while the multi-species microcosm contained above 90%viable cells during the establishment of the community. Based on the live-dead quantification, bacterial viability decreases after each digestion step as the result of acid pH during gastric passage and of the bio-salts contained in the small intestine digestion fluids. The harsh conditions of stomach and small intestine digestion can switch bacteria to viable but not in cultureable cells which are live bacteria that do not either grow or divide.As demonstrated in this figure, viable cells recovered from the mucosal interface are colored blue in the flow-cytometry plot. However, no growth was observed when these mucus samples were plating. The fraction in which bacteria show higher viability rates is the cellular debris as revealed by plate counting.The number of colonies may be variable, but the presence of metabolically active bacteria is found in the less diluted samples. After this development, this technique can be used by researches from the fields of nutrigenomics or pharmacomicrobiomics to study the host microcosmically. Following this protocol, other techniques like transcriptome or metabolic analysis can be performed to obtain mechanistic understanding in the successful colonization process accordingly.After watching this video, you should have a good understanding in how to establish complex in vitro model representative of the digestive processes including the cross talk between the host cells and the rest of the microbiome. Don't forget that working with pathogenic bacteria can be extremely hazardous, and it's important to consider bio-safety precautions.

assessing-viability-synthetic-bacterial-consortium-on-vitro-gut-host

Research

JoVE Journal

Biochemistry

Detection of the pH-dependent Activity of Escherichia coli Chaperone HdeB In Vitro and In Vivo

Bacteria are frequently exposed to environmental changes, such as alterations in pH, temperature, redox status, light exposure or mechanical force. Many of these conditions cause protein unfolding in the cell and have detrimental impact on the survival of the organism. A group of unrelated, stress-specific molecular chaperones have been shown to play essential roles in the survival of these stress conditions. While fully folded and chaperone-inactive before stress, these proteins rapidly unfold and become chaperone-active under specific stress conditions. Once activated, these conditionally disordered chaperones bind to a large number of different aggregation-prone proteins, prevent their aggregation and either directly or indirectly facilitate protein refolding upon return to non-stress conditions. The primary approach for gaining a more detailed understanding about the mechanism of their activation and client recognition involves the purification and subsequent characterization of these proteins using in vitro chaperone assays. Follow-up in vivo stress assays are absolutely essential to independently confirm the obtained in vitro results.
This protocol describes in vitro and in vivo methods to characterize the chaperone activity of E. coli HdeB, an acid-activated chaperone. Light scattering measurements were used as a convenient read-out for HdeB&#39;s capacity to prevent acid-induced aggregation of an established model client protein, MDH, in vitro. Analytical ultracentrifugation experiments were applied to reveal complex formation between HdeB and its client protein LDH, to shed light into the fate of client proteins upon their return to non-stress conditions. Enzymatic activity assays of the client proteins were conducted to monitor the effects of HdeB on pH-induced client inactivation and reactivation. Finally, survival studies were used to monitor the influence of HdeB&#39;s chaperone function in vivo.

Detection of the pH-dependent Activity of Escherichia coli Chaperone HdeB In Vitro and In Vivo

This study describes biophysical, biochemical and molecular techniques to characterize the chaperone activity of Escherichia coli HdeB under acidic pH conditions. These methods have been successfully applied for other acid-protective chaperones such as HdeA and can be modified to work for other chaperones and stress conditions.

Bacteria are frequently exposed to environmental changes, such as alterations in pH, temperature, redox status, light exposure or mechanical force. Many ...

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating these studies, reincorporation of detergent-solubilized membrane proteins into liposomes is a stochastic process where protein topology is impossible to enforce. This paper offers an alternative method to these challenging techniques that utilizes a liposome-based scaffold. Protein solubility is enhanced by deletion of the transmembrane domain, and these amino acids are replaced with a tethering moiety, such as a His-tag. This tether interacts with an anchoring group (Ni2+ coordinated by nitrilotriacetic acid (NTA(Ni2+)) for His-tagged proteins), which enforces a uniform protein topology at the surface of the liposome. An example is presented wherein the interaction between Dynamin-related protein 1 (Drp1) with an integral membrane protein, Mitochondrial Fission Factor (Mff), was investigated using this scaffold liposome method. In this work, we have demonstrated the ability of Mff to efficiently recruit soluble Drp1 to the surface of liposomes, which stimulated its GTPase activity. Moreover, Drp1 was able to tubulate the Mff-decorated lipid template in the presence of specific lipids. This example demonstrates the effectiveness of scaffold liposomes using structural and functional assays and highlights the role of Mff in regulating Drp1 activity.

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

This paper describes a method for assessing the interactions and assemblies of integral membrane proteins in vitro with various partner factors in a lipid-proximal environment.

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating ...

Time-resolved ElectroSpray Ionization Hydrogen-deuterium Exchange Mass Spectrometry for Studying Protein Structure and Dynamics

Intrinsically disordered proteins (IDPs) have long been a challenge to structural biologists due to their lack of stable secondary structure elements. Hydrogen-Deuterium Exchange (HDX) measured at rapid time scales is uniquely suited to detect structures and hydrogen bonding networks that are briefly populated, allowing for the characterization of transient conformers in native ensembles. Coupling of HDX to mass spectrometry offers several key advantages, including high sensitivity, low sample consumption and no restriction on protein size. This technique has advanced greatly in the last several decades, including the ability to monitor HDX labeling times on the millisecond time scale. In addition, by incorporating the HDX workflow onto a microfluidic platform housing an acidic protease microreactor, we are able to localize dynamic properties at the peptide level. In this study, Time-Resolved ElectroSpray Ionization Mass Spectrometry (TRESI-MS) coupled to HDX was used to provide a detailed picture of residual structure in the tau protein, as well as the conformational shifts induced upon hyperphosphorylation.

Conformational flexibility plays a critical role in protein function. Herein, we describe the use of time-resolved electrospray ionization mass spectrometry coupled to hydrogen-deuterium exchange for probing the rapid structural changes that drive function in ordered and disordered proteins.

Intrinsically disordered proteins (IDPs) have long been a challenge to structural biologists due to their lack of stable secondary structure elements. ...

Purification of Biotinylated Cell Surface Proteins from Rhipicephalus microplus Epithelial Gut Cells

Rhipicephalus microplus &#8211; the cattle tick &#8211; is the most significant ectoparasite in terms of economic impact on livestock as a vector of several pathogens. Efforts have been dedicated to the cattle tick control to diminish its deleterious effects, with focus on the discovery of vaccine candidates, such as BM86, located on the surface of the tick gut epithelial cells. Current research focuses upon the utilization of cDNA and genomic libraries, to screen for other vaccine candidates. The isolation of tick gut cells constitutes an important advantage in investigating the composition of surface proteins upon the tick gut cells membrane. This paper constitutes a novel and feasible method for the isolation of epithelial cells, from the tick gut contents of semi-engorged R. microplus. This protocol utilizes TCEP and EDTA to release the epithelial cells from the subepithelial support tissues and a discontinuous density centrifugation gradient to separate epithelial cells from other cell types. Cell surface proteins were biotinylated and isolated from the tick gut epithelial cells, using streptavidin-linked magnetic beads allowing for downstream applications in FACS or LC-MS/MS-analysis.

Purification of Biotinylated Cell Surface Proteins from Rhipicephalus microplus Epithelial Gut Cells

A modified density centrifugation gradient-based methodology was utilized to isolate epithelial cells from Rhipicephalus microplus gut tissue. Surface-bound proteins were biotinylated and purified through streptavidin magnetic beads for utilization in downstream applications.

Rhipicephalus microplus &#8211; the cattle tick &#8211; is the most significant ectoparasite in terms of economic impact on livestock as a vector of ...

In Vitro Polymerization of F-actin on Early Endosomes

Many early endosome functions, particularly cargo protein sorting and membrane deformation, depend on patches of short F-actin filaments nucleated onto the endosomal membrane. We have established a microscopy-based in vitro assay that reconstitutes the nucleation and polymerization of F-actin on early endosomal membranes in test tubes, thus rendering this complex series of reactions amenable to genetic and biochemical manipulations. Endosomal fractions are prepared by floatation in sucrose gradients from cells expressing the early endosomal protein GFP-RAB5. Cytosolic fractions are prepared from separate batches of cells. Both endosomal and cytosolic fractions can be stored frozen in liquid nitrogen, if needed. In the assay, the endosomal and cytosolic fractions are mixed, and the mixture is incubated at 37 &#176;C under appropriate conditions (e.g., ionic strength, reducing environment). At the desired time, the reaction mixture is fixed, and the F-actin is revealed with phalloidin. Actin nucleation and polymerization are then analyzed by fluorescence microscopy. Here, we report that this assay can be used to investigate the role of factors that are involved either in actin nucleation on the membrane, or in the subsequent elongation, branching, or crosslinking of F-actin filaments.

In Vitro Polymerization of F-actin on Early Endosomes

Early endosome functions depend on F-actin polymerization. Here, we describe a microscopy-based in vitro assay that reconstitutes the nucleation and polymerization of F-actin on early endosomal membranes in test tubes, thus rendering this complex series of reactions amenable to biochemical and genetic manipulations.

Many early endosome functions, particularly cargo protein sorting and membrane deformation, depend on patches of short F-actin filaments nucleated onto ...

A Simple Method for High Throughput Chemical Screening in Caenorhabditis Elegans

Caenorhabditis elegans is a useful organism for testing chemical effects on physiology. Whole organism small molecule screens offer significant advantages for identifying biologically active chemical structures that can modify complex phenotypes such as lifespan. Described here is a simple protocol for producing hundreds of 96-well culture plates with fairly consistent numbers of C. elegans in each well. Next, we specified how to use these cultures to screen thousands of chemicals for effects on the lifespan of the nematode C. elegans. This protocol makes use of temperature sensitive sterile strains, agar plate conditions, and simple animal handling to facilitate the rapid and high throughput production of synchronized animal cultures for screening.

A Simple Method for High Throughput Chemical Screening in Caenorhabditis Elegans

Here we describe a simple protocol for rapidly producing hundreds of nematode growth media agar, 96-well culture plates with consistent numbers of Caenorhhabditis elegans per well. These cultures are useful for the phenotypic screening of whole organisms. We focus here on using these cultures to screen chemicals for pro-longevity effects.

Caenorhabditis elegans is a useful organism for testing chemical effects on physiology. Whole organism small molecule screens offer significant advantages ...

A Colorimetric Method for Measuring Iron Content in Plants

Iron, one of the most important micronutrients in living organisms, is involved in basic processes, such as respiration and photosynthesis. Iron content is rather low in all organisms, amounting in plants to about 0.009% of dry weight. To date, one of the most accurate methods for measuring iron concentration in plant tissues is flame absorption atomic spectroscopy. However, this approach is time-consuming and expensive and requires specific equipment not commonly found in plant laboratories. Therefore, a simpler, yet accurate method that can be routinely used is needed. The colorimetric Prussian Blue method is regularly used for qualitative iron staining in animal and plant histological sections. In this study, we adapted the Prussian Blue method for quantitative measurements of iron in tobacco leaves. We validated the accuracy of this method using both atomic spectroscopy and Prussian Blue staining to measure iron content in the same samples and found a linear regression (R2 = 0.988) between the two procedures. We conclude that the Prussian Blue method for quantitative iron measurement in plant tissues is precise, simple, and inexpensive. However, the linear regression presented here may not be appropriate for other plant species, due to potential interactions between the sample and the reagent. Establishment of a regression curve is thus needed for different plant species.

We present a simple and reliable protocol for measuring iron content in plant tissues using the colorimetric Prussian Blue method.

Iron, one of the most important micronutrients in living organisms, is involved in basic processes, such as respiration and photosynthesis. Iron content ...

Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs

Translation initiation is the rate-limiting step of protein synthesis and represents a key point at which cells regulate their protein output. Regulation of protein synthesis is the key to cellular stress-response, and dysregulation is central to many disease states, such as cancer. For instance, although cellular stress leads to the inhibition of global translation by attenuating cap-dependent initiation, certain stress-response proteins are selectively translated in a cap-independent manner. Discreet RNA regulatory elements, such as cellular internal ribosome entry sites (IRESes), allow for the translation of these specific mRNAs. Identification of such mRNAs, and the characterization of their regulatory mechanisms, have been a key area in molecular biology. Toeprinting is a method for the study of RNA structure and function as it pertains to translation initiation. The goal of toeprinting is to assess the ability of in vitro transcribed RNA to form stable complexes with ribosomes under a variety of conditions, in order to determine which sequences, structural elements, or accessory factors are involved in ribosome binding&#8212;a pre-cursor for efficient translation initiation. Alongside other techniques, such as western analysis and polysome profiling, toeprinting allows for a robust characterization of mechanisms for the regulation of translation initiation.

Toeprinting aims to measure the ability of in vitro transcribed RNA to form translation initiation complexes with ribosomes under a variety of conditions. This protocol describes a method for toeprinting mammalian RNA and can be used to study both cap-dependent and IRES-driven translation.

Translation initiation is the rate-limiting step of protein synthesis and represents a key point at which cells regulate their protein output. Regulation ...

Human Peripheral Blood Neutrophil Isolation for Interrogating the Parkinson's Associated LRRK2 Kinase Pathway by Assessing Rab10 Phosphorylation

The leucine rich repeat kinase 2 (LRRK2) is the most frequently mutated gene in hereditary Parkinson&#8217; disease (PD) and all pathogenic LRRK2 mutations result in hyperactivation of its kinase function. Here, we describe an easy and robust assay to quantify LRRK2 kinase pathway activity in human peripheral blood neutrophils by measuring LRRK2-controlled phosphorylation of one of its physiological substrates, Rab10 at threonine 73. The immunoblotting analysis described requires a fully selective and phosphospecific antibody that recognizes the Rab10 Thr73 epitope phosphorylated by LRRK2, such as the MJFF-pRab10 rabbit monoclonal antibody. It uses human peripheral blood neutrophils, because peripheral blood is easily accessible and neutrophils are an abundant and homogenous constituent. Importantly, neutrophils express relatively high levels of both LRRK2 and Rab10. A potential drawback of neutrophils is their high intrinsic serine protease activity, which necessitates the use of very potent protease inhibitors such as the organophosphorus neurotoxin diisopropylfluorophosphate (DIFP) as part of the lysis buffer. Nevertheless, neutrophils are a valuable resource for research into LRRK2 kinase pathway activity in vivo and should be considered for inclusion into PD biorepository collections.

Human Peripheral Blood Neutrophil Isolation for Interrogating the Parkinson&#039;s Associated LRRK2 Kinase Pathway by Assessing Rab10 Phosphorylation

Mutations in the leucine rich repeat kinase 2 gene (LRRK2) cause hereditary Parkinson&#8217;s disease. We have developed an easy and robust method for assessing LRRK2-controlled phosphorylation of Rab10 in human peripheral blood neutrophils. This may help identify individuals with increased LRRK2 kinase pathway activity.

The leucine rich repeat kinase 2 (LRRK2) is the most frequently mutated gene in hereditary Parkinson&#8217; disease (PD) and all pathogenic LRRK2 ...

Visualizing Surface T-Cell Receptor Dynamics Four-Dimensionally Using Lattice Light-Sheet Microscopy

The signaling and function of a cell are dictated by the dynamic structures and interactions of its surface receptors. To truly understand the structure-function relationship of these receptors in situ, we need to visualize and track them on the live cell surface with enough spatiotemporal resolution. Here we show how to use recently developed Lattice Light-Sheet Microscopy (LLSM) to image T-cell receptors (TCRs) four-dimensionally (4D, space and time) at the live cell membrane. T cells are one of the main effector cells of the adaptive immune system, and here we used T cells as an example to show that the signaling and function of these cells are driven by the dynamics and interactions of the TCRs. LLSM allows for 4D imaging with unprecedented spatiotemporal resolution. This microscopy technique therefore can be generally applied to a wide array of surface or intracellular molecules of different cells in biology.

The goal of this protocol is to show how to use Lattice Light-Sheet Microscopy to four-dimensionally visualize surface receptor dynamics in live cells. Here T cell receptors on CD4+ primary T cells are shown.