Name: Detecting Cortex Fragments During Bacterial Spore Germination (Video) | JoVE Journal
Uploaded: 2016-06-25T13:00:00.000+00:00
Duration: 8 min 35 s
Description: Learn a colorimetric assay to quantify cortex fragments and reducing sugars during bacterial spore germination in Clostridium difficile. This accessible method helps researchers study spore dynamics.

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5 minutes

The Project described is supported by Award Number 5R01AI116895 from the National Institute of Allergy and Infectious Diseases. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Allergy and Infectious Diseases or the National Institutes of Health.

1. Generating Samples&#160;
<ol>
	<li>Heat activate C. difficile spores at 65 &#176;C for 30 min and store on ice. 
	Note: C. difficile spores can be produced and purified as described previously7,9,10.</li>
	<li>Prepare the germination solution at X + 1 ml&#160;where X is the number of samples to be taken during the assay. 
	Note: The germination solution is specific to the species of bacteria spore being studied. For assaying C. difficile spore germination, we used a solution of 10 mM Tris (pH 7.5), 150 mM NaCl, 100 mM glycine and 10 mM taurocholic acid in deionized water.</li>
	<li>Before beginning the assay, draw a 1.0 ml sample of the germination solution without spores to serve as a blank for cortex fragment detection.</li>
	<li>Add spores to an OD600 of ~3.0 to the germination solution and vortex quickly. 
	Note: For our germination studies in B. subtilis, we used the same OD600 spores as for C. difficile. 
	Note: This amount of spores worked well for monitoring cortex fragment release during C. difficile spore germination. The amount of spores used in this assay should be determined experimentally for each bacterium or strain.</li>
	<li>Remove a 1.2 ml sample immediately after adding the spores and centrifuge at room temperature for 1 min at 14,000 &#215; g. This is the zero time point.</li>
	<li>Transfer 1.0 ml of the supernatant from the centrifuged sample to a fresh tube for subsequent cortex fragment analysis. 
	Note: Should DPA need to be monitored, remove a separate 100 &#956;l sample for the detection of DPA in the solution using an assay based on terbium fluorescence9,18,19.</li>
	<li>Freeze the collected sample at -80 &#176;C.</li>
	<li>Repeat steps 1.4 and 1.5 at regular intervals until all time points completed. 
	Note: Because of time required for centrifugation and sampling, time points less than 2 min apart were not possible during our procedure, so our sampling intervals were once every 2 min for 14 min.</li>
	<li>As a positive control for reducing sugar detection and quantification, include the following amounts of N-acetylglucosamine (nmol): 0, 12.5, 25, 50, 100, 250, 500, and 5,000. Prepare these samples at the same time as cortex samples and run along with the cortex samples so that the standard curve is relevant to the data generated by germinating spores.</li>
	<li>After all time point samples are collected, lyophilize the samples. 
	Note: We lyophilized our samples in 2 ml screw-cap tubes.</li>
</ol>
2. Measuring Cortex Fragments
<ol>
	<li>Resuspend lyophilized samples in 120 &#181;l of 3 N HCl supplemented with 1% phenol and 0.5% &#946;-mercaptoethanol.</li>
	<li>Transfer the resuspended samples to 2-ml screw-cap tubes. 
	Note: For reproducibility, ensure all the lyophilized sample is resuspended and transferred.</li>
	<li>Incubate the samples in a recirculating water bath at 95 &#176;C for 4 hr.</li>
	<li>After incubation, place the samples on ice until they are cool.</li>
	<li>Neutralize the samples with 120 &#181;l of 3 M NaOH.</li>
	<li>Add 80 &#181;l of a saturated sodium bicarbonate solution and 80 &#181;l of a 5% acetic anhydride solution to each sample and vortex.</li>
	<li>Incubate the samples at room temperature for 10 min.</li>
	<li>Transfer the samples back to the 95 &#176;C water bath for EXACTLY 3 min. 
	Note: This step is time sensitive and longer times can affect downstream signal development.</li>
	<li>Remove samples from the water bath and cool on ice.</li>
	<li>Add 400 &#181;l of 6.54% K2B4O7&#183;4H2O to each tube and vortex.</li>
	<li>Incubate the samples in a recirculating water bath at 95 &#176;C for EXACTLY 7 min. 
	Note: This step is time sensitive and longer times can affect downstream signal development.</li>
	<li>Remove the samples and place on ice for 5 min.</li>
</ol>
3. Color Reagent
<ol>
	<li>While samples are on ice (Step 2.12), prepare the color reagent. Dissolve 0.320 g of p-dimethylaminobenzaldehyde (DMAB; Ehrlich&#39;s reagent) in 1.9 ml of glacial acetic acid. 
	Note: The reagent is time, temperature and light sensitive and should not be made in advance.</li>
	<li>After the DMAB completely dissolves, add 100 &#181;l of 10 N HCl and vortex.</li>
	<li>Add 5 ml of glacial acetic acid and vortex.</li>
</ol>
4. Colorimetric Reaction
<ol>
	<li>Transfer 100 &#181;l of each cooled cortex sample to a new 1.5 ml microcentrifuge tube.</li>
	<li>Add 700 &#181;l of the freshly-prepared color solution to each sample.</li>
	<li>Immediately transfer the samples to a 37 &#176;C water bath and incubate for EXACTLY 20 min.</li>
	<li>Transfer 200 &#181;l of each sample to a clear 96-well plate.</li>
	<li>Quantify the samples at 585 nm on a plate reader. Samples should start at a yellow color and a positive reaction will shift to purple. The more cortex present, the deeper the purple color.</li>
</ol>

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<li>Tan, I. S., Ramamurthi, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Spore+formation+in+Bacillus+subtilis%5BTitle%5D)+AND+%22Environ+Microbiol+Rep%22%5BJournal%5D)">Spore formation in Bacillus subtilis.</a> Environ Microbiol Rep. 6, 212-225 (2014).</li>
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<li>Popham, D. L., Helin, J., Costello, C. E., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Analysis+of+the+peptidoglycan+structure+of+Bacillus+subtilis+endospores%5BTitle%5D)+AND+%22J+Bacteriol%22%5BJournal%5D)">Analysis of the peptidoglycan structure of Bacillus subtilis endospores.</a> J Bacteriol. 178, 6451-6458 (1996).</li>
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<li>Sorg, J. A., Sonenshein, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Bile+salts+and+glycine+as+cogerminants+for+Clostridium+difficile+spores%5BTitle%5D)+AND+%22J.+Bacteriol%22%5BJournal%5D)">Bile salts and glycine as cogerminants for Clostridium difficile spores.</a> J. Bacteriol. 190, 2505-2512 (2008).</li>
<li>Paredes-Sabja, D., Shen, A., Sorg, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Clostridium+difficile+spore+biology%3A+sporulation%2C+germination%2C+and+spore+structural+proteins%5BTitle%5D)+AND+%22Trends+Microbiol%22%5BJournal%5D)">Clostridium difficile spore biology: sporulation, germination, and spore structural proteins.</a> Trends Microbiol. 22 (7), (2014).</li>
<li>Francis, M. B., Allen, C. A., Sorg, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Spore+cortex+hydrolysis+precedes+DPA+release+during+Clostridium+difficile+spore+germination%5BTitle%5D)+AND+%22J+Bacteriol%22%5BJournal%5D)">Spore cortex hydrolysis precedes DPA release during Clostridium difficile spore germination.</a> J Bacteriol. 197 (14), (2015).</li>
<li>Francis, M. B., Allen, C. A., Shrestha, R., Sorg, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Bile+acid+recognition+by+the+Clostridium+difficile+Germinant+Receptor%2C+CspC%2C+is+important+for+establishing+infection%5BTitle%5D)+AND+%22PLoS+Pathog%22%5BJournal%5D)">Bile acid recognition by the Clostridium difficile Germinant Receptor, CspC, is important for establishing infection.</a> PLoS Pathog. 9, e1003356(2013).</li>
<li>Moir, A., Smith, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Genetics+of+bacterial+spore+germination%5BTitle%5D)+AND+%22Annu.+Rev.+Microbiol%22%5BJournal%5D)">The Genetics of bacterial spore germination.</a> Annu. Rev. Microbiol. 44, 531-553 (1990).</li>
<li>Zhang, P., Kong, L., Wang, G., Setlow, P., Li, Y. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Combination+of+Raman+tweezers+and+quantitative+differential+interference+contrast+microscopy+for+measurement+of+dynamics+and+heterogeneity+during+the+germination+of+individual+bacterial+spores%5BTitle%5D)+AND+%22Journal+of+biomedical+optics%22%5BJournal%5D)">Combination of Raman tweezers and quantitative differential interference contrast microscopy for measurement of dynamics and heterogeneity during the germination of individual bacterial spores.</a> Journal of biomedical optics. 15, 056010(2010).</li>
<li>Ghuysen, J. -M., Tipper, D. J., Strominger, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Enzymes+that+degrade+bacterial+cell+walls%5BTitle%5D)+AND+%22Methods+Enzymol%22%5BJournal%5D)">Enzymes that degrade bacterial cell walls.</a> Methods Enzymol. 8, 685-699 (1966).</li>
<li>Park, J. T., Johnson, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+submicrodetermination+of+glucose%5BTitle%5D)+AND+%22J+Biol+Chem%22%5BJournal%5D)">A submicrodetermination of glucose.</a> J Biol Chem. 181, 149-151 (1949).</li>
<li>Thompson, J. S., Shockman, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+modification+of+the+Park+and+Johnson+reducing+sugar+determination+suitable+for+the+assay+of+insoluble+materials%3A+its+application+to+bacterial+cell+walls%5BTitle%5D)+AND+%22Anal+Biochem%22%5BJournal%5D)">A modification of the Park and Johnson reducing sugar determination suitable for the assay of insoluble materials: its application to bacterial cell walls.</a> Anal Biochem. 22, 260-268 (1968).</li>
<li>Paredes-Sabja, D., Setlow, P., Sarker, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((SleC+is+essential+for+cortex+peptidoglycan+hydrolysis+during+germination+of+spores+of+the+pathogenic+bacterium+Clostridium+perfringens%5BTitle%5D)+AND+%22J+Bacteriol%22%5BJournal%5D)">SleC is essential for cortex peptidoglycan hydrolysis during germination of spores of the pathogenic bacterium Clostridium perfringens.</a> J Bacteriol. 191, 2711-2720 (2009).</li>
<li>Paredes-Sabja, D., Sarker, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+the+cortex-lytic+enzyme+SleC+from+non-food-borne+Clostridium+perfringens+on+the+germination+properties+of+SleC-lacking+spores+of+a+food+poisoning+isolate%5BTitle%5D)+AND+%22Can+J+Microbiol%22%5BJournal%5D)">Effect of the cortex-lytic enzyme SleC from non-food-borne Clostridium perfringens on the germination properties of SleC-lacking spores of a food poisoning isolate.</a> Can J Microbiol. 56, 952-958 (2010).</li>
<li>Hindle, A. A., Hall, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Dipicolinic+acid+%28DPA%29+assay+revisited+and+appraised+for+spore+detection%5BTitle%5D)+AND+%22The+Analyst%22%5BJournal%5D)">Dipicolinic acid (DPA) assay revisited and appraised for spore detection.</a> The Analyst. 124, 1599-1604 (1999).</li>
<li>Kort, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Assessment+of+heat+resistance+of+bacterial+spores+from+food+product+isolates+by+fluorescence+monitoring+of+dipicolinic+acid+release%5BTitle%5D)+AND+%22Appl+Environ+Microbiol%22%5BJournal%5D)">Assessment of heat resistance of bacterial spores from food product isolates by fluorescence monitoring of dipicolinic acid release.</a> Appl Environ Microbiol. 71, 3556-3564 (2005).</li>
<li>Elson, L. A., Morgan, W. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+colorimetric+method+for+the+determination+of+glucosamine+and+chondrosamine%5BTitle%5D)+AND+%22The+Biochemical+journal%22%5BJournal%5D)">A colorimetric method for the determination of glucosamine and chondrosamine.</a> The Biochemical journal. 27, 1824-1828 (1933).</li>
<li>Ramirez, N., Abel-Santos, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Requirements+for+germination+of+Clostridium+sordellii+spores+in+vitro%5BTitle%5D)+AND+%22J.+Bacteriol%22%5BJournal%5D)">Requirements for germination of Clostridium sordellii spores in vitro.</a> J. Bacteriol. 192, 418-425 (2010).</li>
<li>Akoachere, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Indentification+of+an+in+vivo+inhibitor+of+Bacillus+anthracis+spore+germination%5BTitle%5D)+AND+%22J.+Biol.+Chem%22%5BJournal%5D)">Indentification of an in vivo inhibitor of Bacillus anthracis spore germination.</a> J. Biol. Chem. 282, 12112-12118 (2007).</li>
<li>Duncan, C. L., Strong, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Improved+medium+for+sporulation+of+Clostridium+perfringens%5BTitle%5D)+AND+%22Appl+Microbiol%22%5BJournal%5D)">Improved medium for sporulation of Clostridium perfringens.</a> Appl Microbiol. 16, 82-89 (1968).</li>
<li>Heffron, J. D., Lambert, E. A., Sherry, N., Popham, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Contributions+of+four+cortex+lytic+enzymes+to+germination+of+Bacillus+anthracis+spores%5BTitle%5D)+AND+%22J+Bacteriol%22%5BJournal%5D)">Contributions of four cortex lytic enzymes to germination of Bacillus anthracis spores.</a> J Bacteriol. 192, 763-770 (2010).</li>
<li>Meador-Parton, J., Popham, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Structural+analysis+of+Bacillus+subtilis+spore+peptidoglycan+during+sporulation%5BTitle%5D)+AND+%22J+Bacteriol%22%5BJournal%5D)">Structural analysis of Bacillus subtilis spore peptidoglycan during sporulation.</a> J Bacteriol. 182, 4491-4499 (2000).</li>
<li>Lambert, E. A., Popham, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Bacillus+anthracis+SleL+%28YaaH%29+protein+is+an+N-acetylglucosaminidase+involved+in+spore+cortex+depolymerization%5BTitle%5D)+AND+%22J+Bacteriol%22%5BJournal%5D)">The Bacillus anthracis SleL (YaaH) protein is an N-acetylglucosaminidase involved in spore cortex depolymerization.</a> J Bacteriol. 190, 7601-7607 (2008).</li>
<li>Wang, S., Shen, A., Setlow, P., Li, Y. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Characterization+of+the+Dynamic+Germination+of+Individual+Clostridium+difficile+Spores+Using+Raman+Spectroscopy+and+Differential+Interference+Contrast+Microscopy%5BTitle%5D)+AND+%22J+Bacteriol%22%5BJournal%5D)">Characterization of the Dynamic Germination of Individual Clostridium difficile Spores Using Raman Spectroscopy and Differential Interference Contrast Microscopy.</a> J Bacteriol. 197, 2361-2373 (2015).</li>
</ol>

The authors have nothing to disclose.

Upon stimulation, spores undergoing the process of germination lose their resistance properties without the need for macromolecular synthesis. When spore germination is triggered, the spore core releases DPA in exchange for water2. Due to the high DPA content of the dormant spore, the spore core is under intense osmotic pressure and the specialized peptidoglycan, cortex, helps prevent the core from swelling by acting, presumably, as a barrier to expansion2.
The method des...

Endospores are metabolically dormant forms of bacteria that allow bacteria to persist in unfavorable environments. In many spore-forming bacteria, spore formation is induced by nutrient deprivation but this process can be controlled by changes to pH, exposure to oxygen or other stresses1. While in their metabolically dormant spore form, bacteria resist UV radiation, desiccation, higher temperatures, and freezing2. Most of the knowledge on the sporulation process comes from studies in the model organism, Bacillus subtilis. The sporulation process begins with DNA replication and the formation of an axial filament3,4. An asymmetric septum then divides the cell into two unequally sized compartments. The larger compartment, the mother cell, engulfs the smaller compartment, the forespore. Both the mother cell and forespore coordinate gene expression to mature the spore and the mother cell eventually lyses, releasing the dormant spore into the surrounding environment1.
The spore structure and composition is conserved across many bacterial species. The spore core has a lower water content than the vegetative cell and is rich with dipicolinic acid (DPA)1,2. During spore formation, DPA is pumped into the spore core in exchange for water. Surrounding the core is an inner spore membrane where, in most spore forming bacteria, the receptors which recognize the small molecules that stimulate germination (germinants) are located2. Located just outside the spore&#39;s inner membrane is a layer of cell wall peptidoglycan. A specialized peptidoglycan layer (cortex) surrounds the cell wall peptidoglycan and is composed of many of the same components as cell wall peptidoglycan [alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)]. However, approximately 50% of the NAM residues in the cortex have been converted to muramic-&#948;-lactam5,6. During spore germination, these muramic-&#948;-lactam residues are recognized by the spore cortex lytic enzymes (SCLEs), thus allowing the cortex to be degraded (a process essential to complete germination) but not the cell wall. Surrounding the cortex is an outer membrane and several layers of coat proteins 2.
Controlling the process of germination is critically important for spore-forming bacteria. Germination is initiated when germinant receptors interact with their respective germinants2. In many spore-forming bacteria, these germinants are amino acids, sugars, nucleotides, ions or combinations thereof2. C. difficile spore germination is initiated by combinations of certain bile acids, [e.g., taurocholic acid (TA)] and amino acids (e.g., glycine)7-10. Though there are differences between the C. difficile germination pathway and the pathways studied in other spore-forming bacteria, such as B. subtilis, common to all is the absolute requirement to degrade the spore cortex to allow a vegetative cell to grow from the germinated spore2,8. Cortex degradation can be accomplished by the SCLEs CwlJ/SleB (as found in B. subtilis) or SleC (as found in many Clostridia). Cortex hydrolysis reduces the constraint on the cell wall and the spore. This allows for full core rehydration, a necessary step in reactivating many of the proteins necessary for cellular metabolism 2.
When spores germinate, the dormant spore changes from a phase-bright state to a phase-dark state and this process can be measured by a change in optical density (OD) at 600 nm11. A previous report suggests that much of this change in OD is due to the release of DPA from the spore12. During our recent study, we sought to compare the timing of C. difficile spore germination and monitored the release of DPA and cortex fragments9. For this study it was critical to monitor the release of cortex fragments as they began to be released by germinating spores.
The colorimetric assay used here was based upon a method for detecting sugars with reducing ends developed Ghuysen et al.13. Because others have described protocols for the detection of reducing sugars14 or have modified those protocols15, the literature on this subject can be confusing. Here, we detail a step-by-step method for the colorimetric detection of reducing sugars liberated from germinating C. difficile spores. Though this study uses C. difficile spores, the reducing sugars released during the germination of spores from other spore-forming bacteria are able to be detected with this protocol9,16,17.

<table><tbody><tr><td>2.0 ml screw cap tube</td><td>USA scientific</td><td>1420-3700</td><td></td></tr><tr><td>p1000 Eppendorf pipet</td><td>Eppendorf</td><td></td><td></td></tr><tr><td>p200 Eppendorf pipet</td><td>Eppendorf</td><td></td><td></td></tr><tr><td>p20 Eppendorf pipet</td><td>Eppendorf</td><td></td><td></td></tr><tr><td>100 - 1,250 &amp;#956;l pipet tips</td><td>VWR</td><td>89079-486</td><td></td></tr><tr><td>1 - 200 &amp;#956;ll pipet tips</td><td>VWR</td><td>89079-458</td><td></td></tr><tr><td>N-acetyl-D-glucosamine</td><td>Sigma</td><td>A3286-25G</td><td></td></tr><tr><td>Hydrochloric Acid - 10 N</td><td>BDH-Aristar</td><td>BDH3032-3.8LP</td><td></td></tr><tr><td>Acetic Anhydride</td><td>Alfa Aesar</td><td>L04295</td><td></td></tr><tr><td>Sodium Bicarbonate</td><td>BDH</td><td>BDH0280-500G</td><td></td></tr><tr><td>Potassium Tetraborate tetrahydrate</td><td>Alfa Aesar</td><td>39435</td><td></td></tr><tr><td>Sodium Hydroxide</td><td>BDH</td><td>BDH8019-500G</td><td></td></tr><tr><td>4-(Dimethylamino)benzaldehyde</td><td>Sigma</td><td>156477-100G</td><td></td></tr><tr><td>Saturated Phenol</td><td>Fisher</td><td>BP1750-400</td><td></td></tr><tr><td>2-Mercaptoethanol</td><td>Aldrich</td><td>M6250-100ML</td><td></td></tr><tr><td>SpectraMax M3</td><td>Molecular Devices</td><td></td><td></td></tr><tr><td>Acetic Acid, Glacial</td><td>BDH</td><td>BDH3098-3.8LP</td><td></td></tr><tr><td>Heated, Circulating Water Bath</td><td>VWR Scientific</td><td>Model 1136</td><td></td></tr><tr><td>Microtest 96</td><td>Falcon</td><td>353072</td><td>96 well clear tissue culture plates</td></tr><tr><td>Culture tubes</td><td>VWR</td><td>89000-506</td><td></td></tr><tr><td>Lyophilizer</td><td></td><td></td><td></td></tr><tr><td>Heat Blocks</td><td></td><td></td><td></td></tr><tr><td>Vortex Machine</td><td></td><td></td><td></td></tr></tbody></table>

detecting cortex fragments during bacterial spore germination

Detecting Cortex Fragments During Bacterial Spore Germination

The process of endospore germination in Clostridium difficile, and other Clostridia, increasingly is being found to differ from the model spore-forming bacterium, Bacillus subtilis. Germination is triggered by small molecule germinants and occurs without the need for macromolecular synthesis. Though differences exist between the mechanisms of spore germination in species of Bacillus and Clostridium, a common requirement is the hydrolysis of the peptidoglycan-like cortex which allows the spore core to swell and rehydrate. After rehydration, metabolism can begin and this, eventually, leads to outgrowth of a vegetative cell. The detection of hydrolyzed cortex fragments during spore germination can be difficult and the modifications to the previously described assays can be confusing or difficult to reproduce. Thus, based on our recent report using this assay, we detail a step-by-step protocol for the colorimetric detection of cortex fragments during bacterial spore germination.

Table 1 shows typical results using NAG standards. Data are used to generate a standard curve. Table 2 shows typical results from a germination assay in germination buffer supplemented with 100 mM glycine and 10 mM TA (germination-promoting conditions) or 100 mM glycine only (non-germinating conditions). In the absence of TA, C. difficile spores do not germinate and there is little change in the presence of cortex fragments in the solution. Howev...

Herein, we describe a colorimetric assay to detect the presence of reducing sugars during bacterial spore germination.

The process of endospore germination in Clostridium difficile, and other Clostridia, increasingly is being found to differ from the model spore-forming ...

The overall goal of this step-by-step protocol is to quantify the abundance of cortex fragments or reducing sugars during bacterial spore germination. This method will detail the steps required to detect the presence of cortex fragments or reducing sugars during spore germination. The main advantage of this technique is most laboratories have the reagents and equipment necessary to successfully complete the protocol.Begin this procedure by placing a tube of Clostridium difficile spores in a heating block and incubating it 65 degrees Celsius for 30 minutes. After the incubation, place the tube on ice. The germination solution is specific to the species of bacterial spore being studied.For assaying C.difficile spore germination, we use a solution of 10 millimolar Tris at pH 7.5 with 150 millimolar of sodium chloride, 100 millimolar glycine, and 10 millimolar taurocholic acid in deionized water. Prepare one milliliter of germination solution per sample plus an additional one milliliter. Before beginning the assay, transfer one milliliter of the germination solution to a microcentrifuge tube and set it aside.This will serve as a blank for cortex fragment detection. Next, to the germination solution, add spores to an OD600 of about 3.0 and briefly vortex. This amount of spores works well for moderating cortex fragment release during C.difficile spore germination.Immediately after adding the spores, remove a 1.2 milliliter sample to a new microcentrifuge tube and put it into the centrifuge. Then centrifuge at room temperature for one minute at 14, 000 times G.This is the zero time point. After the spin, transfer one milliliter of the supernatant to a fresh two-milliliter screw-cap tube and freeze it at negative 80 degrees Celsius.Repeat the process of taking aliquots, spinning down, and freezing at regular intervals until the sample has been collected for each time point. Because of time required for centrifugation and sampling, time points of less than two minutes are not possible during this procedure, so these samples are taken once every two minutes for 14 minutes. While preparing the cortex samples, should dipicolinic acid need to be monitored, remove a separate 100 microliter sample and dispense in a microcentrifuge tube on ice.Also prepare samples for generating a standard curve with the following amounts of N-acetylglucosamine. Zero, 12.5, 25, 50, 100, 250, 500, and 5, 000 nanomoles in germination solution. After a sample has been collected for each time point, remove the samples from the freezer and lyophilize them along with the blank and the standard curve samples.Then store all of the samples at negative 80 degrees Celsius until use. On the day of the assay, resuspend the lyophilized samples, including the controls and standard curve samples, in 120 microliters of hydrochloric acid with phenol and beta-mercaptoethanol. Next, transfer all of the resuspended samples to fresh two-milliliter screw cap tubes.Then incubate them in a recirculating water bath at 95 degrees Celsius for four hours. After the incubation, place the samples on ice until they are cool. Then add 120 microliters of three molar sodium hydroxide to neutralize them.Next, add 80 microliters of a saturated sodium bicarbonate solution and 80 microliters of a 5%acetic anhydride solution to each sample and vortex it. Then incubate the samples at room temperature for 10 minutes. Following the incubation, transfer the samples back to the 95 degree Celsius water bath for exactly three minutes.Note that this step is time sensitive and longer times can affect downstream signal development. Remove the samples from the water bath and cool them on ice. Add 400 microliters of 6.54%potassium tetraborate tetrahydrate to each tube and vortex.Incubate the samples in a recirculating water bath at 95 degrees Celsius for exactly seven minutes. This step is also time sensitive. Remove the samples and place them on ice for five minutes.While the samples are on ice, prepare the color reagent. Dissolve 0.320 grams of DMAB in 1.9 milliliters of glacial acetic acid. Note that this reagent is time, temperature, and light sensitive and should not be made in advance.After the DMAB completely dissolves, add 100 microliters of 10 normal hydrochloric acid and vortex the sample. Then add five milliliters of glacial acetic acid and vortex again. For the colorimetric reaction, transfer 100 microliters of each cooled cortex or control sample to a new 1.5 milliliter microcentrifuge tube.Add 700 microliters of the freshly prepared color solution to each sample. Immediately transfer the samples to a 37 degree Celsius water bath and incubate the samples for exactly 20 minutes. After the incubation, transfer 200 microliters of each sample to a clear 96-well plate.The samples should be yellow in color to begin with but will shift to purple if reducing sugar, which indicates the presence of cortex, is present. Here, many of the samples do not show a visible purple color. However, the 250, 500, and 5, 000 nanomole samples appear visually different from the negative control zero nanomole.Using a plate reader, determine the absorbance at 585 nanometers. When measured in an OD of 585 nanometers, the signal generated from the standard samples best fits a linear regression. This table shows typical results using N-acetylglucosamine standards.These data were then used to generate the standard curve shown here. A germination assay was performed under germination promoting conditions with germination buffer supplemented with 100 millimolar glycine and 10 millimolar taurocholic acid. In non-germinating conditions, 100 millimolar glycine only.In the absence of taurocholic acid, C.Difficile spores do not germinate, and there is little change in the presence of cortex fragments in the solution. However, in the presence of both taurocholic acid and glycine, C.difficile spores germinate and release cortex fragments into the solution. This is absorbed as an increase in the OD585 over time of the reacted samples.The quantity of cortex fragments released during this assay was calculated using a standard curve. As can be seen here in this assay, most of the cortex was hydrolyzed or released by 15 minutes post-germinant exposure. This suggests that most of the spores have germinated in this time frame.After watching this video, you should have a good understanding of how to detect cortex fragments or reducing sugars in a germination solution during bacterial spore germination. While attempting this procedure, it is important to pay close attention to reaction times so that the assay will develop correctly.

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Research

JoVE Journal

Immunology and Infection

Source: Francis, M. B., et al. Detecting Cortex Fragments During Bacterial Spore Germination. J. Vis. Exp. (2016).This video demonstrates a colorimetric method to detect cortex degradation during bacterial spore germination by measuring the release of reducing sugars over time. Using N-acetylglucosamine standards and time-point samples, the assay quantifies sugar concentration through a purple chromogenic reaction, indicating the extent of cortex hydrolysis.

Colorimetric Detection of Cortex Degradation During Bacterial Spore Germination

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Learn a colorimetric assay to quantify cortex fragments and reducing sugars during bacterial spore germination in Clostridium difficile. This accessible method helps researchers study spore dynamics.

Detecting Cortex Fragments During Bacterial Spore Germination

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