Name: visualization of germinosomes and the inner membrane in bacillus subtilis spores
Uploaded: 2019-04-15T13:00:00
Description: Watch this Scientific Journal Video about Visualization of Germinosomes and the Inner Membrane in Bacillus subtilis Spores at JoVE.com

The authors thank Christiaan Zeelenberg for his assistance during the SIM imaging. JW acknowledges the China Scholarship Council for a PhD fellowship and thanks Irene Stellingwerf for her help during the primary stage of imaging.

1. B. subtillis&#160;Sporulation (Timing: 7 Days Before Microscopic Observation)
<ol>
	<li>Day 1
	<ol>
		<li>Streak a bacterial culture on a Luria-Bertani Broth (LB) agar plate (1% tryptone, 0.5% yeast extract, 1% NaCl, 1% agar)13 and incubate overnight at 37 &#176;C to obtain single colonies. Use the B. subtilis KGB80 (PS4150 gerKA gerKC gerKB-mCherry cat, gerD-gfp kan) strain and its parent background strain B. subtilis PS4150 (PS832 &#9...

<ol>
	<li>Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Germination+of+spores+of+Bacillus+species:+what+we+know+and+do+not+know.">Germination of spores of Bacillus species: what we know and do not know.</a> Journal of Bacteriology. 196 (7), 1297-1305 (2014).</li><li>Setlow, P., Wang, S., Li, Y. -. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Germination+of+spores+of+the+orders+Bacillales+and+Clostridiales.">Germination of spores of the orders Bacillales and Clostridiales.</a> Annual Review of Microbiology. 71 (1), (2017).</li><li>Vepachedu, V. R., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+interactions+between+nutrient+germinant+receptors+and+SpoVA+proteins+of+Bacillus+subtilis+spores.">Analysis of interactions between nutrient germinant receptors and SpoVA proteins of Bacillus subtilis spores.</a> FEMS Microbiology Letters. 274 (1), 42-47 (2007).</li><li>Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Summer+meeting+2013&#8211;when+the+sleepers+wake:+the+germination+of+spores+of+Bacillus+species.">Summer meeting 2013&#8211;when the sleepers wake: the germination of spores of Bacillus species.</a> Journal of Applied Microbiology. 115 (6), 1251-1268 (2013).</li><li>Cowan, A. E., 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=Lipids+in+the+inner+membrane+of+dormant+spores+of+Bacillus+species+are+largely+immobile.">Lipids in the inner membrane of dormant spores of Bacillus species are largely immobile.</a> Proceedings of the National Academy of Sciences of the United States of America. 101 (20), 7733-7738 (2004).</li><li>Loison, 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=Direct+investigation+of+viscosity+of+an+atypical+inner+membrane+of+Bacillus+spores:+a+molecular+rotor/FLIM+study.">Direct investigation of viscosity of an atypical inner membrane of Bacillus spores: a molecular rotor/FLIM study.</a> Biochimica et Biophysica Acta (BBA)-Biomembranes. 1828 (11), 2436-2443 (2013).</li><li>Griffiths, K. K., Zhang, J., Cowan, A. E., Yu, J., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Germination+proteins+in+the+inner+membrane+of+dormant+Bacillus+subtilis+spores+colocalize+in+a+discrete+cluster.">Germination proteins in the inner membrane of dormant Bacillus subtilis spores colocalize in a discrete cluster.</a> Molecular Microbiology. 81 (4), 1061-1077 (2011).</li><li>Troiano, A. J., Zhang, J., Cowan, A. E., Yu, J., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+the+dynamics+of+a+Bacillus+subtilis+spore+germination+protein+complex+during+spore+germination+and+outgrowth.">Analysis of the dynamics of a Bacillus subtilis spore germination protein complex during spore germination and outgrowth.</a> Journal of Bacteriology. 197 (2), 252-261 (2015).</li><li>Wegel, E., 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=Imaging+cellular+structures+in+super-resolution+with+SIM,+STED+and+Localisation+Microscopy:+A+practical+comparison.">Imaging cellular structures in super-resolution with SIM, STED and Localisation Microscopy: A practical comparison.</a> Scientific Reports. 6, 27290 (2016).</li><li>Pandey, 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=Live+cell+imaging+of+germination+and+outgrowth+of+individual+Bacillus+subtilis+spores;+the+effect+of+heat+stress+quantitatively+analyzed+with+SporeTracker.">Live cell imaging of germination and outgrowth of individual Bacillus subtilis spores; the effect of heat stress quantitatively analyzed with SporeTracker.</a> PloS One. 8 (3), e58972 (2013).</li><li>Demmerle, 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=Strategic+and+practical+guidelines+for+successful+structured+illumination+microscopy.">Strategic and practical guidelines for successful structured illumination microscopy.</a> Nature Protocols. 12 (5), 988-1010 (2017).</li><li>Ball, G., 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=SIMcheck:+a+toolbox+for+successful+super-resolution+structured+illumination+microscopy.">SIMcheck: a toolbox for successful super-resolution structured illumination microscopy.</a> Scientific Reports. 5, 15915 (2015).</li><li>Bertani, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=STUDIES+ON+LYSOGENESIS+I.:+The+Mode+of+Phage+Liberation+by+Lysogenic+Escherichia+coli1.">STUDIES ON LYSOGENESIS I.: The Mode of Phage Liberation by Lysogenic Escherichia coli1.</a> Journal of Bacteriology. 62 (3), 293 (1951).</li><li>Pandey, 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=Quantitative+analysis+of+the+effect+of+specific+tea+compounds+on+germination+and+outgrowth+of+Bacillus+subtilis+spores+at+single+cell+resolution.">Quantitative analysis of the effect of specific tea compounds on germination and outgrowth of Bacillus subtilis spores at single cell resolution.</a> Food Microbiology. 45, 63-70 (2015).</li><li>Zheng, 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=Bacillus+subtilis+spore+inner+membrane+proteome.">Bacillus subtilis spore inner membrane proteome.</a> Journal of Proteome Research. 15 (2), 585-594 (2016).</li><li>Vepachedu, V. R., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+of+SpoVAD+to+the+inner+membrane+of+spores+of+Bacillus+subtilis.">Localization of SpoVAD to the inner membrane of spores of Bacillus subtilis.</a> Journal of Bacteriology. 187 (16), 5677-5682 (2005).</li><li>Schouten, 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=Imaging+dendritic+spines+of+rat+primary+hippocampal+neurons+using+structured+illumination+microscopy.">Imaging dendritic spines of rat primary hippocampal neurons using structured illumination microscopy.</a> Journal of Visualized Experiments: JoVE. (87), (2014).</li><li>Mukaka, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+guide+to+appropriate+use+of+correlation+coefficient+in+medical+research.">A guide to appropriate use of correlation coefficient in medical research.</a> Malawi Medical Journal. 24 (3), 69-71 (2012).</li><li>Stewart, K. A., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Numbers+of+individual+nutrient+germinant+receptors+and+other+germination+proteins+in+spores+of+Bacillus+subtilis.">Numbers of individual nutrient germinant receptors and other germination proteins in spores of Bacillus subtilis.</a> Journal of Bacteriology. 195 (16), 3575-3582 (2013).</li><li>Laflamme, 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=Flow+cytometry+analysis+of+germinating+Bacillus+spores,+using+membrane+potential+dye.">Flow cytometry analysis of germinating Bacillus spores, using membrane potential dye.</a> Archives of Microbiology. 183 (2), 107-112 (2005).</li><li>Magge, A., Setlow, B., Cowan, A. E., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+dye+binding+by+and+membrane+potential+in+spores+of+Bacillus+species.">Analysis of dye binding by and membrane potential in spores of Bacillus species.</a> Journal of Applied Microbiology. 106 (3), 814-824 (2009).</li><li>Ghosh, S., Scotland, M., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Levels+of+germination+proteins+in+dormant+and+superdormant+spores+of+Bacillus+subtilis.">Levels of germination proteins in dormant and superdormant spores of Bacillus subtilis.</a> Journal of Bacteriology. 194 (9), 2221-2227 (2012).</li><li>Abhyankar, W. 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=The+influence+of+sporulation+conditions+on+the+spore+coat+protein+composition+of+Bacillus+subtilis+Spores.">The influence of sporulation conditions on the spore coat protein composition of Bacillus subtilis Spores.</a> Frontiers in microbiology. 7, 1636 (2016).</li><li>Rose, 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=Comparison+of+the+properties+of+Bacillus+subtilis+spores+made+in+liquid+or+on+agar+plates.">Comparison of the properties of Bacillus subtilis spores made in liquid or on agar plates.</a> Journal of Applied Microbiology. 103 (3), 691-699 (2007).</li><li>Stewart, K. A., Yi, X., Ghosh, S., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Germination+protein+levels+and+rates+of+germination+of+spores+of+Bacillus+subtilis+with+overexpressed+or+deleted+genes+encoding+germination+proteins.">Germination protein levels and rates of germination of spores of Bacillus subtilis with overexpressed or deleted genes encoding germination proteins.</a> J Bacteriol. 194 (12), 3156-3164 (2012).</li><li>Ramirez-Peralta, A., Zhang, P., Li, Y. -. q., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+sporulation+conditions+on+the+germination+and+germination+protein+levels+of+Bacillus+subtilis+spores.">Effects of sporulation conditions on the germination and germination protein levels of Bacillus subtilis spores.</a> Applied and Environmental Microbiology. 78 (8), 2689-2697 (2012).</li><li>Laue, M., Han, H. -. M., Dittmann, C., Setlow, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intracellular+membranes+of+bacterial+endospores+are+reservoirs+for+spore+core+membrane+expansion+during+spore+germination.">Intracellular membranes of bacterial endospores are reservoirs for spore core membrane expansion during spore germination.</a> Scientific Reports. 8, 11388 (2018).</li><li>Strahl, H., B&#252;rmann, F., Hamoen, L. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+actin+homologue+MreB+organizes+the+bacterial+cell+membrane.">The actin homologue MreB organizes the bacterial cell membrane.</a> Nature Communications. 5, (2014).</li><li>Strahl, H., Hamoen, L. 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&#160;The protocol presented contains a standard 3D-SIM procedure for analysis of FM4-64 stained B. subtilis spores that includes sporulation, slide preparation and imaging processes. In addition, the protocol describes a modified SIMcheck (ImageJ)-assisted 3D imaging process for SIM microscopy of B. subtilis spore germinosomes labeled with fluorescent reporters. The latter procedure allowed us to observe this dim substructure with enhanced contrast. By coupling two imaging procedures, it is possible to...

Spores of the orders Bacillales and Clostridiales are metabolically dormant and extraordinarily resistant to harsh decontamination regimes, but unless they germinate, cannot cause deleterious effects in humans1. In nutrient germinant triggered germination of Bacillus subtilis (B. subtilis) spores, the initiation event is germinant binding to germinant receptors (GRs) located in the spore&#8217;s inner membrane (IM). Subsequently, the GRs transduce signals to the SpoVA channel protein also located in the IM. This results in the onset of the exchange of spore core pyridine-2,6-dicarboxylic acid (dipicolinic acid; DPA; comprising 20% of spore core dry wt) for water via the SpoVA channel. Subsequently, the DPA release triggers the activation of cortex peptidoglycan hydrolysis, and additional water uptake follows2,3,4. These events lead to mechanical stress on the coat layers, its subsequent rupture, the onset of outgrowth and, finally, vegetative growth. However, the exact molecular details of the germination process are still far from resolved.
A major question about spore germination concerns the biophysical properties of the lipids surrounding the IM germination proteins as well as the IM SpoVA channel proteins. This largely immobile IM lipid bilayer is the main permeability barrier for many small molecules, including toxic chemical preservatives, some of which exert their action in the spore core or vegetative cell cytoplasm5,6. The IM lipid bilayer is likely in a gel state, although there is a significant fraction of mobile lipids in the IM5. The spore&#8217;s IM also has the potential for significant expansion5. Thus, the surface area of the IM increases 1.6-fold upon germination without additional membrane synthesis and is accompanied by the loss of this membrane&#8217;s characteristic low permeability and lipid immobility5,6.
While the molecular details of the activation of germination proteins and organization of IM lipids in spores are attractive topics for study, the small size of B. subtilis spores and the relatively low abundance of germination proteins, pose a challenge to microscopic analyses. Griffiths et al. compelling epifluorescence microscope evidence, using fluorescent reporters fused to germination proteins, suggests that in B. subtilis spores the scaffold protein GerD organizes three GR subunits (A, B and C) for the GerA, B and K GRs, in a cluster7. They coined the term &#8216;germinosome&#8217; for this cluster of germination proteins and described the structures as ~300 nm large IM protein foci8. Upon initiation of spore germination, fluorescent germinosome foci ultimately change into larger disperse fluorescent patterns, with &#62;75% of spore populations displaying this pattern in spores germinated for 1 h with L-valine8. Note that the paper mentioned above used averaged images from dozens of consecutive fluorescent pictures, to gain statistical power and overcome the hurdle of low fluorescent signals observed during imaging. This visualization of these structures in bacterial spores was at the edge of what is technically feasible with classical microscopic tools and neither an evaluation of the amount of foci in a single spore nor their more detailed subcellular localization was possible with this approach.
Here, we demonstrate the use of Structured Illumination Microscopy (SIM) to obtain a detailed visualization and quantification of the germinosome(s) in spores of B. subtilis, as well as of their IM lipid domains9. The protocol also contains instructions for the sporulation, slide preparation and image analysis by SIMcheck (v1.0, an imageJ plugin) as well as ImageJ10,11,12.

<table>
	<tbody>
		<tr>
			<td>Air dried glass slides</td>
			<td>Menzel Gl&#228;ser</td>
			<td>630-2870</td>
			<td></td>
		</tr>
		<tr>
			<td>APO TIRF N20R8 100&#215; oil objective (NA=1.49)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>B. subtilis KGB80 (PS4150 gerKA gerKC gerKB-mCherry cat, gerD-gfp kan)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>B. subtilis PS4150 (PS832 &#916;gerE::spc, &#916;cotE::tet)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Erlenmeyer flasks 1 L</td>
			<td>Sigma-Aldrich</td>
			<td>Z567868</td>
			<td></td>
		</tr>
		<tr>
			<td>Erlenmeyer flasks 250 mL</td>
			<td>Sigma-Aldrich</td>
			<td>Z723088</td>
			<td></td>
		</tr>
		<tr>
			<td>FluoSpheres carboxylate-modified microspheres</td>
			<td>Invitrogen, 0.1 &#956;m</td>
			<td>F8803</td>
			<td></td>
		</tr>
		<tr>
			<td>FM4-64</td>
			<td>Thermo Fisher Scientific</td>
			<td>F34653</td>
			<td></td>
		</tr>
		<tr>
			<td>Histodenz nonionic density gradient medium</td>
			<td>Sigma-Aldrich</td>
			<td>D2158</td>
			<td></td>
		</tr>
		<tr>
			<td>Image J</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>iXON3 DU-897 X-6515 CCD camera</td>
			<td>Andor Technology</td>
			<td></td>
			<td>https://imagej.net/Welcome</td>
		</tr>
		<tr>
			<td>LB Agar</td>
			<td>Sigma-Aldrich</td>
			<td>L2897</td>
			<td></td>
		</tr>
		<tr>
			<td>Microfuge tubes 1.5 mL</td>
			<td>Thermo Fisher Scientific</td>
			<td>3451PK</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope imaging software</td>
			<td>Nikon, Japan</td>
			<td>NIS-Element AR 4.51.01</td>
			<td></td>
		</tr>
		<tr>
			<td>MilliQ Ultrapure Deminerilzed Water</td>
			<td>Millipore</td>
			<td>Milli-Q IQ 7003</td>
			<td></td>
		</tr>
		<tr>
			<td>Nikon Eclipse Ti microscope</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Polypropylene Screw Cap Bottle 180 mL</td>
			<td>Thermo Fisher Scientific</td>
			<td>75003800</td>
			<td></td>
		</tr>
		<tr>
			<td>Precision Coverslips</td>
			<td>Paul Marienfeld</td>
			<td>117650</td>
			<td></td>
		</tr>
		<tr>
			<td>Round Bottom tubes 15 mL</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td>Nunc TM</td>
		</tr>
		<tr>
			<td>Screw cap tubes 50 mL</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td>Nunc TM</td>
		</tr>
	</tbody>
</table>

visualization of germinosomes and the inner membrane in bacillus subtilis spores

The small size of spores and the relatively low abundance of germination proteins, cause difficulties in their microscopic analyses using epifluorescence microscopy. Super-resolution three-dimensional Structured Illumination Microscopy (3D-SIM) is a promising tool to overcome this hurdle and reveal the molecular details of the process of germination of Bacillus subtilis (B. subtilis) spores. Here, we describe the use of a modified SIMcheck (ImageJ)-assistant 3D imaging process and fluorescent reporter proteins for SIM microscopy of B. subtilis spores&#8217; germinosomes, cluster(s) of germination proteins. We also present a (standard)3D-SIM imaging procedure for FM4-64 staining of B. subtilis spore membranes. By using these procedures, we obtained unsurpassed resolution for germinosome localization and show that &#62;80% of B. subtilis KGB80 dormant spores obtained after sporulation on defined minimal MOPS medium have one or two GerD-GFP and GerKB-mCherry foci. Bright foci were also observed in FM4-64 stained spores&#8217; 3D-SIM images suggesting that inner membrane lipid domains of different fluidity likely exist. Further studies that use double labeling procedures with membrane dyes and germinosome reporter proteins to assess co-localization and thus get an optimal overview of the organization of Bacillus germination proteins in the inner spore membrane are possible.

The current protocol presents a SIM microscope imaging procedure for bacterial spores. The sporulation and slide preparation procedures were carried out as shown in Figure 1 before imaging. Later, the imaging and analysis procedures were applied both for dim (fluorescent protein labeled germination proteins) and bright (lipophilic probe stained IM) spore samples as shown in the following text.
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Watch this Scientific Journal Video about Visualization of Germinosomes and the Inner Membrane in Bacillus subtilis Spores at JoVE.com

Visualization of Germinosomes and the Inner Membrane in Bacillus subtilis Spores

Germinant receptor proteins cluster in &#8216;germinosomes&#8217; in the inner membrane of Bacillus subtilis spores. We describe a protocol using super resolution microscopy and fluorescent reporter proteins to visualize germinosomes. The protocol also identifies spore inner membrane domains that are preferentially stained with the membrane dye FM4-64.

Visualization of Germinosomes and the Inner Membrane in Bacillus subtilis Spores

The small size of spores and the relatively low abundance of germination proteins, cause difficulties in their microscopic analyses using epifluorescence ...

Super-resolution structured illumination microscopy, 3D-SIM, is an innovative technique for the visualization of fluorescent reporter proteins of germination receptor clusters in spore membranes. Using these procedures, unsurpassed resolution of germinosome localization and spore inner membrane lipid domains can be achieved. The technique will be demonstrated by PhD student Juan Wen and Master of Science student Raymond Pasman of our laboratory.Before beginning the procedure, clean high-precision coverslips with one-molar hydrochloric acid for 30 minutes in a gently shaking water bath, followed by two, five-minute washes in ultrapure Type 1 water. After the second wash, place the coverslips in 100%ethanol for about three minutes before drying the coverslips and verifying their clarity. Then, clean glass microscope slides with 70%ethanol for one minute before allowing the slides to dry and verifying their clarity.For fluorescent microsphere and spore imaging, first pre-warm two slides on a 70-degree Celsius heating block for a few seconds before adding a 70-degree Celsius, 65-microliter droplet of sterilized 2%agarose onto one of the slides. Place the other slide on top to spread the agarose between the slides. After five minutes, remove one of the slides and cut the dried agarose into a one-by-one-centimeter section.Add one times 10 to the eighth fluorescent microspheres or spores in 0.4 microliters of sterile, ultrapure Type 1 water to the agarose, and place a high-precision coverslip onto the patch using the coverslip to slide the patch off of the slide onto the coverslip surface. Then, fix a 65-microliter, 1.5-by-1.6-centimeter Gene Frame onto a dried slide, and place the coverslip onto the frame, closing all of the corners of the frame. For imaging of the samples, place the slide onto a structured illumination microscope equipped with a 100X oil objective, and focus on the 100-nanometer fluorescent microspheres.Adjust the correction ring on the 100x objective until a symmetric point spread function is obtained to minimize blurring of the images, and select a field of view with approximately 10 round fluorescent microspheres. Apply a grating focus adjustment for the designated excitation wavelengths, in this case, 561 and 488 nanometers, as a guide for the image analysis software before focusing on the spores with the transmission light. Capture a transmission light image in the 16x average mode with 20-millisecond exposures for each image.Then, capture 3D-structured illumination microscope raw fluorescent images of the spores with the 3D-SIM illumination mode. For slice reconstruction, click Param on the structured illumination pad tab sheet to open the N-SIM Slice Reconstruction window. Follow the suggested instructions, and click on the appropriate controls to set the illumination modulation contrast to auto, the high-resolution noise suppression to one, and the out of the focus blur suppression to 0.05 as starting points.Then, click Reconstruct Slice to reconstruct the image and evaluate the quality of the reconstructed images by the fast Fourier-transformed images and reconstruction score that are displayed after the reconstruction. Adjust the high-resolution noise from 0.1 to five and the out of the focus blur suppression from 0.01 to 0.5 until the best parameter settings are obtained. Then, click Apply to apply the changes.Click Close to close the window. Open an FM4-64 stained PS4150 spores raw image. Then, click Reconstruct Slice to execute the slice reconstruction, and save the reconstructed image.To convert the 3D-SIM raw images of the KGB80 geminosome into pseudo-widefield images, left-click on the ImageJ SIMcheck plugin and select Raw Data SI and Pseudo Widefield. Randomly select about 25 spores in each inverted transmission image for a later germinosome analysis in the fluorescent pseudo-widefield images until approximately 350 spores have been selected. Then, use ImageJ to assess the maximum intensity for each fluorescent signal expressed by each group of spores and the integrated intensity of each 3D spore image.To analyze the pseudo-widefield images of the KGB80 germinosome, use the mean integrated intensity value of seven stacks as the integrated signal intensity of the KGB80 spore. Then, determine the background intensities by imaging the PS4150 background strain using identical settings, and regard the fluorescent spots in individual KGB80 spores as germinosome foci when they are clearly distinguishable from the background. In this representative experiment, two foci of the GerD-GFP fluorescing spores appeared in different stacks with three total GerD-GFP foci observed in the compositive Z3 stack.Here, a spore with only one GerD-GFP focal point in the spore was observed. In total, around 40 to 50%of the spores had two or one GerD-GFP and GerKB-mCherry cluster, respectively. While the integrated intensity of the GerD-GFP scaffold protein was different between different populations, the integrated intensity of GerKB-mCherry was about the same in different populations.When the spore had multiple foci, the maximum fluorescence intensity of GerD-GFP and GerKB-mCherry foci tended to decrease, and the maximum fluorescence of all of the bright spots, regarded as the germinosome foci, was higher than the maximum auto-fluorescence of the PS4150 spores. Notably, brighter FM4-64 spots similar to germinosome foci appear in both intact and decoated PS4150 spores, suggesting that these brighter FM4-64 spots might be involved in the clustering of germinosome proteins in the inner membrane. Adding spores to the agarose and placing agarose into the frame requires a continuously and careful fluid movement for these minis materials.The conversion of 3D-SIM raw images of the KGB80 germinosome into pseudo-widefield images and their interpretation requires expert knowledge on spore biology. Our structured illumination microscopy procedure can be applied to the imaging of low abundant proteins or dim fluorescence reporters in different bacterias or other band materials. The organization of the germinosome can now be studied using double labeling procedures to assess co-localization of Bacillus germination proteins and specific membrane domains.

visualization-germinosomes-inner-membrane-bacillus-subtilis

Research

JoVE Journal

Bioengineering

Optical Mapping of Action Potentials and Calcium Transients in the Mouse Heart

The mouse heart is a popular model for cardiovascular studies due to the existence of low cost technology for genetic engineering in this species. Cardiovascular physiological phenotyping of the mouse heart can be easily done using fluorescence imaging employing various probes for transmembrane potential (Vm), calcium transients (CaT), and other parameters. Excitation-contraction coupling is characterized by action potential and intracellular calcium dynamics; therefore, it is critically important to map both Vm and CaT simultaneously from the same location on the heart1-4. Simultaneous optical mapping from Langendorff perfused mouse hearts has the potential to elucidate mechanisms underlying heart failure, arrhythmias, metabolic disease, and other heart diseases. Visualization of activation, conduction velocity, action potential duration, and other parameters at a myriad of sites cannot be achieved from cellular level investigation but is well solved by optical mapping1,5,6. In this paper we present the instrumentation setup and experimental conditions for simultaneous optical mapping of Vm and CaT in mouse hearts with high spatio-temporal resolution using state-of-the-art CMOS imaging technology. Consistent optical recordings obtained with this method illustrate that simultaneous optical mapping of Langendorff perfused mouse hearts is both feasible and reliable.

This paper details the dissection procedure, instrumental setup, and experimental conditions during optical mapping of transmembrane potential (Vm) and intracellular calcium transient (CaT) in intact isolated Langendorff perfused mouse hearts.

The mouse heart is a popular model for cardiovascular studies due to the existence of low cost technology for genetic engineering in this species. ...

Visualization of Cortex Organization and Dynamics in Microorganisms, using Total Internal Reflection Fluorescence Microscopy

TIRF microscopy has emerged as a powerful imaging technology to study spatio-temporal dynamics of fluorescent molecules in vitro and in living cells1. The optical phenomenon of total internal reflection occurs when light passes from a medium with high refractive index into a medium with low refractive index at an angle larger than a characteristic critical angle (i.e. closer to being parallel with the boundary). Although all light is reflected back under such conditions, an evanescent wave is created that propagates across and along the boundary, which decays exponentially with distance, and only penetrates sample areas that are 100-200 nm near the interface2. In addition to providing superior axial resolution, the reduced excitation of out of focus fluorophores creates a very high signal to noise ratios and minimizes damaging effects of photobleaching2,3. Being a widefield technique, TIRF also allows faster image acquisition than most scanning based confocal setups.
At first glance, the low penetration depth of TIRF seems to be incompatible with imaging of bacterial and fungal cells, which are often surrounded by thick cell walls. On the contrary, we have found that the cell walls of yeast and bacterial cells actually improve the usability of TIRF and increase the range of observable structures4-8. Many cellular processes can therefore be directly accessed by TIRF in small, single-cell microorganisms, which often offer powerful genetic manipulation techniques. This allows us to perform in vivo biochemistry experiments, where kinetics of protein interactions and activities can be directly assessed in living cells.
We describe here the individual steps required to obtain high quality TIRF images for Saccharomyces cerevisiae or Bacillus subtilis cells. We point out various problems that can affect TIRF visualization of fluorescent probes in cells and illustrate the procedure with several application examples. Finally, we demonstrate how TIRF images can be further improved using established image restoration techniques.

Total Internal Reflection Fluorescence (TIRF) microscopy is a powerful approach to observe structures close to the cell surface at high contrast and temporal resolution. We demonstrate how TIRF can be employed to study protein dynamics at the cortex of cell wall-enclosed bacterial and fungal cells.

TIRF microscopy has emerged as  a powerful imaging technology to study spatio-temporal dynamics of fluorescent molecules  in vitro and in living cells1. ...

Membrane-SPINE: A Biochemical Tool to Identify Protein-protein Interactions of Membrane Proteins In Vivo

Membrane proteins are essential for cell viability and are therefore important therapeutic targets1-3. Since they function in complexes4, methods to identify and characterize their interactions are necessary5. To this end, we developed the Membrane Strep-protein interaction experiment, called Membrane-SPINE6. This technique combines in vivo cross-linking using the reversible cross-linker formaldehyde with affinity purification of a Strep-tagged membrane bait protein. During the procedure, cross-linked prey proteins are co-purified with the membrane bait protein and subsequently separated by boiling. Hence, two major tasks can be executed when analyzing protein-protein interactions (PPIs) of membrane proteins using Membrane-SPINE: first, the confirmation of a proposed interaction partner by immunoblotting, and second, the identification of new interaction partners by mass spectrometry analysis. Moreover, even low affinity, transient PPIs are detectable by this technique. Finally, Membrane-SPINE is adaptable to almost any cell type, making it applicable as a powerful screening tool to identify PPIs of membrane proteins.

Membrane-SPINE: A Biochemical Tool to Identify Protein-protein Interactions of Membrane Proteins In Vivo

A biochemical approach is described to identify in vivo protein-protein interactions (PPI) of membrane proteins. The method combines protein cross-linking, affinity purification and mass spectrometry, and is adaptable to almost any cell type or organism. With this approach, even the identification of transient PPIs becomes possible.

Membrane proteins are essential for cell viability and are therefore important therapeutic targets1-3. Since they function in complexes4, methods to ...

Quantification of Global Diastolic Function by Kinematic Modeling-based Analysis of Transmitral Flow via the Parametrized Diastolic Filling Formalism

Quantitative cardiac function assessment remains a challenge for physiologists and clinicians.&#160;Although historically invasive methods have comprised the only means available, the development of noninvasive imaging modalities (echocardiography, MRI, CT) having high temporal and spatial resolution provide a new window for quantitative diastolic function assessment. Echocardiography is the agreed upon standard for diastolic function assessment, but indexes in current clinical use merely utilize selected features of chamber dimension (M-mode) or blood/tissue motion (Doppler) waveforms without incorporating the physiologic causal determinants of the motion itself.&#160;The recognition that all left ventricles (LV) initiate filling by serving as mechanical suction pumps allows global diastolic function to be assessed based on laws of motion that apply to all chambers. What differentiates one heart from another are the parameters of the equation of motion that governs filling. Accordingly, development of the Parametrized Diastolic Filling (PDF) formalism&#160;has shown that the entire range of clinically observed early transmitral flow (Doppler E-wave) patterns are extremely well fit by the laws of damped oscillatory motion.&#160;This permits analysis of individual E-waves in accordance with a causal mechanism (recoil-initiated suction) that yields three (numerically) unique lumped parameters whose physiologic analogues are chamber stiffness (k), viscoelasticity/relaxation (c), and load (xo).&#160;The recording of transmitral flow (Doppler E-waves) is standard practice in clinical cardiology and, therefore, the echocardiographic recording method is only briefly reviewed. Our focus is on determination of the PDF parameters from routinely recorded E-wave data.&#160;As the highlighted results indicate, once the PDF parameters have been obtained from a suitable number of load varying E-waves, the investigator is free to use the parameters or construct indexes from the parameters (such as stored energy 1/2kxo2, maximum A-V pressure gradient kxo, load independent index of diastolic function, etc.) and select the aspect of physiology or pathophysiology to be quantified.

Accurate, causality-based quantification of global diastolic function has been achieved by kinematic modeling-based analysis of transmitral flow via the Parametrized Diastolic Filling (PDF) formalism. PDF generates unique stiffness, relaxation,&#160;and load parameters and elucidates &#39;new&#39; physiology while providing sensitive and specific indexes of dysfunction.

Quantitative cardiac function assessment remains a challenge for physiologists and clinicians.&#160;Although historically invasive methods have comprised ...

Analysis of Tubular Membrane Networks in Cardiac Myocytes from Atria and Ventricles

In cardiac myocytes a complex network of membrane tubules - the transverse-axial tubule system (TATS) - controls deep intracellular signaling functions. While the outer surface membrane and associated TATS membrane components appear to be continuous, there are substantial differences in lipid and protein content. In ventricular myocytes (VMs), certain TATS components are highly abundant contributing to rectilinear tubule networks and regular branching 3D architectures. It is thought that peripheral TATS components propagate action potentials from the cell surface to thousands of remote intracellular sarcoendoplasmic reticulum (SER) membrane contact domains, thereby activating intracellular Ca2+ release units (CRUs). In contrast to VMs, the organization and functional role of TATS membranes in atrial myocytes (AMs) is significantly different and much less understood. Taken together, quantitative structural characterization of TATS membrane networks in healthy and diseased myocytes is an essential prerequisite towards better understanding of functional plasticity and pathophysiological reorganization. Here, we present a strategic combination of protocols for direct quantitative analysis of TATS membrane networks in living VMs and AMs. For this, we accompany primary cell isolations of mouse VMs and/or AMs with critical quality control steps and direct membrane staining protocols for fluorescence imaging of TATS membranes. Using an optimized workflow for confocal or superresolution TATS image processing, binarized and skeletonized data are generated for quantitative analysis of the TATS network and its components. Unlike previously published indirect regional aggregate image analysis strategies, our protocols enable direct characterization of specific components and derive complex physiological properties of TATS membrane networks in living myocytes with high throughput and open access software tools. In summary, the combined protocol strategy can be readily applied for quantitative TATS network studies during physiological myocyte adaptation or disease changes, comparison of different cardiac or skeletal muscle cell types, phenotyping of transgenic models, and pharmacological or therapeutic interventions.

In cardiac myocytes, tubular membrane structures form intracellular networks. We describe optimized protocols for i) isolation of myocytes from mouse heart including quality control, ii) live cell staining for state-of-the-art fluorescence microscopy, and iii) direct image analysis to quantify the component complexity and the plasticity of intracellular membrane networks.

In cardiac myocytes a complex network of membrane tubules - the transverse-axial tubule system (TATS) - controls deep intracellular signaling functions. ...

Luminescence Resonance Energy Transfer to Study Conformational Changes in Membrane Proteins Expressed in Mammalian Cells

Luminescence Resonance Energy Transfer, or LRET, is a powerful technique used to measure distances between two sites in proteins within the distance range of 10-100 &#197;. By measuring the distances under various ligated conditions, conformational changes of the protein can be easily assessed. With LRET, a lanthanide, most often chelated terbium, is used as the donor fluorophore, affording advantages such as a longer donor-only emission lifetime, the flexibility to use multiple acceptor fluorophores, and the opportunity to detect sensitized acceptor emission as an easy way to measure energy transfer without the risk of also detecting donor-only signal. Here, we describe a method to use LRET on membrane proteins expressed and assayed on the surface of intact mammalian cells. We introduce a protease cleavage site between the LRET fluorophore pair. After obtaining the original LRET signal, cleavage at that site removes the specific LRET signal from the protein of interest allowing us to quantitatively subtract the background signal that remains after cleavage. This method allows for more physiologically relevant measurements to be made without the need for purification of protein.

We describe here an improved Luminescence Resonance Energy Transfer (LRET) method where we introduce a protease cleavage site between the donor and acceptor fluorophore sites. This modification allows us to obtain specific LRET signals arising from membrane proteins of interest, allowing for the study of membrane proteins without protein purification.

Luminescence Resonance Energy Transfer, or LRET, is a powerful technique used to measure distances between two sites in proteins within the distance range ...

Three-Dimensionally Printed Microfluidic Cross-flow System for Ultrafiltration/Nanofiltration Membrane Performance Testing

Minimization and management of membrane fouling is a formidable challenge in diverse industrial processes and other practices that utilize membrane technology. Understanding the fouling process could lead to optimization and higher efficiency of membrane based filtration. Here we show the design and fabrication of an automated three-dimensionally (3-D) printed microfluidic cross-flow filtration system that can test up to 4 membranes in parallel. The microfluidic cells were printed using multi-material photopolymer 3-D printing technology, which used a transparent hard polymer for the microfluidic cell body and incorporated a thin rubber-like polymer layer, which prevents leakages during operation. The performance of ultrafiltration (UF), and nanofiltration (NF) membranes were tested and membrane fouling could be observed with a model foulant bovine serum albumin (BSA). Feed solutions containing BSA showed flux decline of the membrane. This protocol may be extended to measure fouling or biofouling with many other organic, inorganic or microbial containing solutions. The microfluidic design is especially advantageous for testing materials that are costly or only available in small quantities, for example polysaccharides, proteins, or lipids due to the small surface area of the membrane being tested. This modular system may also be easily expanded for high throughput testing of membranes.&#160;

Design and fabrication of a three-dimensionally (3-D) printed microfluidic cross-flow filtration system is demonstrated. The system is used to test performance and observe fouling of ultrafiltration and nanofiltration (thin film composite) membranes.

Minimization and management of membrane fouling is a formidable challenge in diverse industrial processes and other practices that utilize membrane ...

Treatment of Ligament Constructs with Exercise-conditioned Serum: A Translational Tissue Engineering Model

In vitro experiments are essential to understand biological mechanisms; however, the gap between monolayer tissue culture and human physiology is large, and translation of findings is often poor. Thus, there is ample opportunity for alternative experimental approaches. Here we present an approach in which human cells are isolated from human anterior cruciate ligament tissue remnants, expanded in culture, and used to form engineered ligaments. Exercise alters the biochemical milieu in the blood such that the function of many tissues, organs and bodily processes are improved. In this experiment, ligament construct culture media was supplemented with experimental human serum that has been &#39;conditioned&#39; by exercise. Thus the intervention is more biologically relevant since an experimental tissue is exposed to the full endogenous biochemical milieu, including binding proteins and adjunct compounds that may be altered in tandem with the activity of an unknown agent of interest. After treatment, engineered ligaments can be analyzed for mechanical function, collagen content, morphology, and cellular biochemistry. Overall, there are four major advantages versus traditional monolayer culture and animal models, of the physiological model of ligament tissue that is presented here. First, ligament constructs are three-dimensional, allowing for mechanical properties (i.e., function) such as ultimate tensile stress, maximal tensile load, and modulus, to be quantified. Second, the enthesis, the interface between boney and sinew elements, can be examined in detail and within functional context. Third, preparing media with post-exercise serum allows for the effects of the exercise-induced biochemical milieu, which is responsible for the wide range of health benefits of exercise, to be investigated in an unbiased manner. Finally, this experimental model advances scientific research in a humane and ethical manner by replacing the use of animals, a core mandate of the National Institutes of Health, the Center for Disease Control, and the Food and Drug Administration.

We present a model of ligament tissue in which three-dimensional constructs are treated with the human exercise-conditioned serum and analyzed for collagen content, function, and cellular biochemistry.

In vitro experiments are essential to understand biological mechanisms; however, the gap between monolayer tissue culture and human physiology is large, ...

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and dampen loads in the spine. The IVD consists of a proteoglycan-rich nucleus pulposus (NP) and a collagen-rich annulus fibrosis (AF) sandwiched by cartilaginous end-plates. Together with the adjacent vertebrae, the vertebrae-IVD structure forms a functional spine unit (FSU). These microstructures contain unique cell types as well as unique extracellular matrices. Whole organ culture of the FSU preserves the native extracellular matrix, cell differentiation phenotypes, and cellular-matrix interactions. Thus, organ culture techniques are particularly useful for investigating the complex biological mechanisms of the IVD. Here, we describe a high-throughput approach for culturing whole lumbar mouse FSUs that provides an ideal platform for studying disease mechanisms and therapies for the IVD. Furthermore, we describe several applications that utilize this organ culture method to conduct further studies including contrast-enhanced microCT imaging and three-dimensional high-resolution finite element modeling of the IVD.

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Whole organ culture of the intervertebral disc (IVD) preserves the native extracellular matrix, cell phenotypes, and cellular-matrix interactions. Here we describe an IVD culture system using mouse lumbar and caudal IVDs in their functional spinal units and several applications utilizing this system.

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and ...

A Protocol for Decellularizing Mouse Cochleae for Inner Ear Tissue Engineering

In mammals, mechanosensory hair cells that facilitate hearing lack the ability to regenerate, which has limited treatments for hearing loss. Current regenerative medicine strategies have focused on transplanting stem cells or genetic manipulation of surrounding support cells in the inner ear to encourage replacement of damaged stem cells to correct hearing loss. Yet, the extracellular matrix (ECM) may play a vital role in inducing and maintaining function of hair cells, and has not been well investigated. Using the cochlear ECM as a scaffold to grow adult stem cells may provide unique insights into how the composition and architecture of the extracellular environment aids cells in sustaining hearing function. Here we present a method for isolating and decellularizing cochleae from mice to use as scaffolds accepting perfused adult stem cells. In the current protocol, cochleae are isolated from euthanized mice, decellularized, and decalcified. Afterward, human Wharton&#39;s jelly cells (hWJCs) that were isolated from the umbilical cord were carefully perfused into each cochlea. The cochleae were used as bioreactors, and cells were cultured for 30 days before undergoing processing for analysis. Decellularized cochleae retained identifiable extracellular structures, but did not reveal the presence of cells or noticeable fragments of DNA. Cells perfused into the cochlea invaded most of the interior and exterior of the cochlea and grew without incident over a duration of 30 days. Thus, the current method can be used to study how cochlear ECM affects cell development and behavior.

The goal of this protocol is to demonstrate an effective method to decellularize and decalcify mouse cochleae for utilization as scaffolds for tissue engineering applications.

In mammals, mechanosensory hair cells that facilitate hearing lack the ability to regenerate, which has limited treatments for hearing loss. Current ...