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. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane+potential+is+important+for+bacterial+cell+division.">Membrane potential is important for bacterial cell division.</a> Proceedings of the National Academy of Sciences of the United States of America. 107 (27), 12281-12286 (2010).</li><li>Swarge, B. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term="One-Pot"+sample+processing+methodfor+proteome-wide+analysis+of+microbial+cells+and+spores.">"One-Pot" sample processing methodfor proteome-wide analysis of microbial cells and spores.</a> Proteomics Clinical Applications. (5), 1700169 (2018).</li></ol>

&#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.
<stro...

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

9.6K 조회수.  University of Amsterdam. 초분해능 구조화 조명 현미경 검사법인 3D-SIM은 포자 막에서 발아 수용체 클러스터의 형광 기자 단백질을 시각화하는 혁신적인 기술입니다. 이러한 절차를 사용하여 발거국화 및 포자 내부 막 지질 도메인의 타의 추종을 불허하는 해상도를 달성할 수 있습니다. 이 기술은 박사 과정 학생 후안 웬과 과학 학생 레이몬드 파스만의 우리의 실험실에 의해 입증될 것입니다.시...