Name: live cell fluorescence microscopy to observe essential processes during microbial cell growth
Uploaded: 2017-11-24T15:00:00
Description: Watch this Scientific Journal Video about Live Cell Fluorescence Microscopy to Observe Essential Processes During Microbial Cell Growth at JoVE.com

We thank Michael VanNieuwenhze (Indiana University) for the gift of the FDAAs used in Figure 2 and Figure 4. We thank members of the Brown lab for feedback during the preparation of this manuscript. Research in the Brown lab on A. tumefaciens cell growth and division is supported by the National Science Foundation (IOS1557806).

1. Growth of A. tumefaciens Strains
<ol>
	<li>Culturing A. tumefaciens strains
	<ol>
		<li>Use a sterile wooden stick or pipet tip to inoculate 1 mL of ATGN growth media (see materials list for the recipe) with a single colony of the desired strain. 
		NOTE: For A. tumefaciens depletion strains, the ATGN should contain 1 mM IPTG as an inducer to maintain biosynthesis of the essential protein.</li>
		<li>Grow the A. tumefaciens strains overnight in ATGN at 28 &#1...

This protocol contains a series of procedures for the investigation of A. tumefaciens wildtype, mutant, and depletion strains. It is worth noting that all of the procedures listed in the protocol section can be readily adapted for other bacterial strains with additional modifications to account for growth media, temperatures, and growth rates.
The use of target-specific dyes is a valuable tool for providing a detailed characterization of cell-cycle events in bacterial cells. Here, pep...

Progression through the bacterial cell cycle requires the coordination of many processes including membrane and cell wall biosynthesis, DNA replication and segregation, and cell division. To fully understand the complexity of bacterial cell biology, it is necessary to study these essential events; however, this is a non-trivial task since cell viability is compromised when key components of these pathways are mutagenized. Epifluorescence microscopy coupled with target-specific dyes is a powerful approach to probe these essential processes in wildtype and mutant bacterial strains.
Peptidoglycan-specific dyes include fluorescent antibiotics (vancomycin-FL, bocillin-FL) and fluorescent-d-amino acids (for example, 7-hydroxycoumarin-3-carboxylic acid-3-amino-d-alanine, HADA; 4-chloro-7-nitrobenzofurazan-3-amino- d-alanine, NADA; tetramethylrhodamine-3-amino-d-alanine; TADA). In Gram-positive bacteria, the use of sublethal concentrations of fluorescent antibiotic analogs to probe sites of peptidoglycan biosynthesis has been an effective strategy to reveal peptidoglycan insertion patterns1,2,3,4. While fluorescent vancomycin labeling has been used to gain insights into the peptidoglycan insertion patterns in fixed Gram-negative bacteria5, the outer membrane generally provides a permeability barrier that prevents the use of fluorescent antibiotics as a probe for peptidoglycan biosynthesis in live cells. In contrast, short pulses of fluorescent-d-amino acids or d-amino acids with biorthogonal functional groups covalently label regions of recent peptidoglycan insertion in a wide range of living bacterial cells6,7. Patterns of peptidoglycan insertion that have been observed with synthetic d-amino acids include punctate and septal (Escherichia coli and Bacillus subtilis), polar and septal (Agrobacterium tumefaciens and Listeria monocytogenes), septal only (Staphylococcus aureus), and apical (Streptomyces venezuelae)6,7. These observations indicate that bacteria exhibit diverse patterns of cell wall biogenesis and that the use of synthetic d-amino acids as probes for examining growth patterning is a valuable strategy in many bacteria.
Dyes that label bacterial chromosomes include the deoxyribonucleic acid (DNA) specific minor groove binder (4,6-diamidino-2-phenylindole; DAPI) and high affinity cyanine dyes (Green and Orange; see materials list). DAPI staining of fixed cells assists in enumeration of bacteria from environmental samples8, whereas DAPI staining of live cells is used to indicate bacterial viability9. In contrast, cyanine dyes such as Orange and Green are frequently described as membrane impermeant &#34;dead&#34; cell stains to enumerate non-viable cells9. Remarkably, when these reagents are used to probe the morphology of the bacterial nucleoid during cell growth, DAPI, Orange, and Green were all shown to be membrane permeant and capable of labeling live cells10. In live E. coli cells, DAPI staining of DNA appears diffuse due to auto-fluorescence from the cytoplasm and repeated exposures of DAPI-stained cells to ultraviolet (UV) light perturbs the nucleoid structure10. Staining E. coli or B. subtilis with Orange reveals that this dye is membrane permeant and provides long-lasting fluorescence upon binding to DNA in live cells without impacting cell growth, DNA replication, or chromosome segregation10. These observations suggest that cyanine DNA dyes can be used to monitor the morphology of nucleoids during cell growth in many bacteria.
Phospholipid-specific stryl dyes such as N-(3-triethylammoniumpropyl) -4-(6-(4-(diethylamino) phenyl)hexatrienyl)pyridinium dibromide (4-64; see materials list) are cationic compounds and associate preferentially with negatively charged phospholipids such as cardiolipin and phosphatidylglycerol11. Distinct patterns are observed when 4-64 is used to label the membrane of different bacteria. In Escherichia coli, 4-64 is enriched in the poles, in bands along the lateral wall, and in the division sites of late pre-divisional cells12. In Bacillus subtilis, 4-64 labeling enables the visualization of lipid spirals13. In Agrobacterium tumefaciens, 4-64 labels the outer membrane and is observed in a characteristic &#34;horseshoe&#34; pattern in which the growth pole is devoid of labeling14,15. These observations indicate that these bacteria exhibit heterogeneous lipid distributions due to the presence of lipid domains which contribute to cellular asymmetry. Changes in 4-64 labeling patterns such as the presence of diffuse labeling, blebs or vesicles, invaginations, or membrane shrinkage can be informative in characterizing mutants that impact the distribution or biosynthesis of lipids.
Beyond staining cells, determining the function of proteins participating in essential processes is necessary. The characterization of essential proteins is technically challenging because it is not possible to delete essential genes and study the phenotypic consequences. Thus, alternative approaches that deplete the protein have emerged. For example, an essential gene can be put under the control of an inducible promoter rather than its native promoter. Inducible promoters are responsive to small molecules such as; zinc16, isopropyl &#946;-d-1-thiogalactopyranoside (IPTG)17,18,19,20,21, arabinose22, vanillate17,23, and xylose23, thus the transcription of the target gene ceases and the protein of interest is depleted when the inducer is removed. Alternative approaches for depleting essential proteins of interest include synthetic riboswitches24 which use small molecule-RNA interactions to hinder transcription of target genes, CRISPR interference25,26 to block transcription of target genes, and inducible protein degradation27,28 which uses peptide tags to target proteins for degradation by the ClpXP protease. Depletion strains provide only a short time for characterization before the cells lose viability, therefore, microscopic imaging of cells over time during protein depletion is a powerful approach for characterization. Indeed, microscopy of living bacterial cells has enabled researchers to gain insights into fundamental biological processes, including the mechanisms of cell shape maintenance, secretion, and compartmentalization29.
A. tumefaciens is a bacterial plant pathogen30 and natural genetic engineer31,32. Thus, mechanisms related to pathogenicity, including host-pathogen interactions33,34,35, secretion36, and host transformation30,31,37 have been extensively investigated. To design strategies that prevent A. tumefaciens mediated disease or enhance plant transformation, the processes essential for A. tumefaciens survival need to be better understood. The use of target-specific dyes and the recent development of a protein depletion strategy for A. tumefaciens18 provides a means to investigate essential processes.
Here, detailed protocols for microscopic analysis of wildtype, mutant, and protein depletion strains of A. tumefaciens are provided. The first two protocols describe how to prepare cells and label them with target-specific dyes. The third protocol provides step-by-step directions for preparing agarose pads (Figure 1) and imaging the bacterial cells (Figure 2, Figure 3, Figure 4). These protocols may also be suitable for other bacteria with additional adaptations to account for different media conditions, growth rates, oxygen requirements, and cell structures.

<table>
	<tbody>
		<tr>
			<td>Bacterial Strains</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Agrobacterium tumefaciens C58</td>
			<td>ATCC</td>
			<td>33970</td>
			<td>Watson B, Currier TC, Gordon MP, Chilton MD, Nester EW. 1975. Plasmid required for virulence of Agrobacterium tumefaciens. J Bacteriol 123:255-264.</td>
		</tr>
		<tr>
			<td>Agrobacterium tumefaciens C58&#916;tetRA::mini-Tn7T-GM-Ptac-ctrA &#916;ctrA</td>
			<td></td>
			<td></td>
			<td>Figueroa-Cuilan W, Daniel JJ, Howell M, Sulaiman A, Brown PJB. 2016. Mini-Tn7 insertion in an artificial attTn7 site enables depeltion of the essentail master regulator CtrA in the phytopathogen Agrobacterium tumefaciens. Appl Environ Microbiol. 82:5015-5025.</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Media Components</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ATGN Minimal Medium</td>
			<td></td>
			<td></td>
			<td>To 1 L of sterilized water add 50 ml 20X Buffer, 50 ml 20X Salts, 12.5 ml 40% glucose. For plates, add 15 g Bacto Agar to 1 L of water and autoclave. Cool to 55 &#176;C and add 50 ml 20X Buffer, 50 ml 20X Salts, 12.5 ml 40% glucose.</td>
		</tr>
		<tr>
			<td>20X AT Buffer</td>
			<td></td>
			<td></td>
			<td>Add 214 g/L KH2PO4 to water and adjust pH to 7.0 with sodium hydroxide. Autoclave.</td>
		</tr>
		<tr>
			<td>NaOH</td>
			<td>Fisher BioReagents</td>
			<td>BP359</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Fisher Chemical</td>
			<td>P288</td>
			<td></td>
		</tr>
		<tr>
			<td>20X AT Salts</td>
			<td></td>
			<td></td>
			<td>Add 40 g/L (NH4)2SO4, 3.2 g/L MgSO4&#8226;7H2O, 0.2 g/L CaCl2&#8226;2H2O, and 0.024 g/L MnSO4&#8226;H2O to water. Autoclave.</td>
		</tr>
		<tr>
			<td>(NH4)2SO4</td>
			<td>Fisher Chemical</td>
			<td>A701</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4&#8226;7H2O</td>
			<td>Fisher BioReagents</td>
			<td>BP213</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2&#8226;2H2O</td>
			<td>Fisher BioReagents</td>
			<td>BP510</td>
			<td></td>
		</tr>
		<tr>
			<td>MnSO4&#8226;H2O</td>
			<td>Fisher Chemical</td>
			<td>M114</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Fisher Chemical</td>
			<td>D16</td>
			<td>Prepare 40% stock in water. Filter sterilize.</td>
		</tr>
		<tr>
			<td>Bacto Agar</td>
			<td>Fisher BioReagents</td>
			<td>BP1423</td>
			<td>Add 15 g to 1 L of water when preparing plates.</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Optional Media Additives</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Kanamycin</td>
			<td>GoldBio</td>
			<td>K-120</td>
			<td>Prepare as a 100 mg/ml stock solution in water and filter sterilize. Use at final concentration of 200 &#181;g/ml.</td>
		</tr>
		<tr>
			<td>IPTG</td>
			<td>GoldBio</td>
			<td>I2481C5</td>
			<td>Prepare as a 1 M stock solution in water and filter sterilize. Use at final concentration of 1 mM as needed for induction.</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Microscopy Materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope Slides</td>
			<td>Fisherbrand</td>
			<td>12-550D</td>
			<td>25 X 75 X 1.0 mm. Clean with Sparkle glass cleaner.</td>
		</tr>
		<tr>
			<td>Microscope Cover Glass</td>
			<td>Fisherbrand</td>
			<td>12-541-B</td>
			<td>22 X 22 mm. No. 1.5. Clean with Sparkle glass cleaner.</td>
		</tr>
		<tr>
			<td>Sparkle Glass Cleaner</td>
			<td>Home Depot</td>
			<td>203261385</td>
			<td>Ammonia and alcohol free.</td>
		</tr>
		<tr>
			<td>Ultra Pure Agarose</td>
			<td>Invitrogen</td>
			<td>16500-100</td>
			<td>Add to water, PBS, or media to a final concentration of 1 - 1.5%. Melt in microwave and place on 70 C</td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Fisher BioReagents</td>
			<td>BP399500</td>
			<td>10X solution to be diluted to 1X with sterile water.</td>
		</tr>
		<tr>
			<td>Parafilm</td>
			<td>Bemis</td>
			<td>PM-999</td>
			<td>Laboratory film used as gasket in agarose pad preparation.</td>
		</tr>
		<tr>
			<td>VALAP</td>
			<td></td>
			<td></td>
			<td>Add equal weights of lanolin, parafin wax, and petroleum jelly to a conical tube. Heat tube in 70 &#176;C dry, bead or water bath to melt and mix. Apply VALAP while still molten.</td>
		</tr>
		<tr>
			<td>Lanolin Butter</td>
			<td>SAAQIN</td>
			<td>SQ-LAB-R1</td>
			<td></td>
		</tr>
		<tr>
			<td>Petroleum Jelly</td>
			<td>Target Corp.</td>
			<td>06-17644</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin Wax</td>
			<td>Crafty Candles</td>
			<td>263012</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Target-specific dyes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DMSO</td>
			<td>Fisher BioReagents</td>
			<td>BP231-1</td>
			<td>Use to dilute stock solutions of dyes as needed.</td>
		</tr>
		<tr>
			<td>FDAAs (NADA, HADA,TADA)</td>
			<td></td>
			<td></td>
			<td>FDAAs can be synthesized or acquired through agreement with Mike VanNieuwenhze (Indiana University). Prepare 100 mM stock solution in DMSO. Use at a final concentration of 5 mM.</td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>ThermoFisher Scientific</td>
			<td>62247</td>
			<td>Prepare 1 mg/ml stock solution in DMSO. Use at final concentration of 1 &#181;g/ml.</td>
		</tr>
		<tr>
			<td>SYTOX Orange Nucleic Acid Stain</td>
			<td>Invitrogen</td>
			<td>S11368</td>
			<td>Stock concentration is 5 mM in DMSO. Use at final concentration of 5 &#181;M.</td>
		</tr>
		<tr>
			<td>FM4-64</td>
			<td>Invitrogen</td>
			<td>T3166</td>
			<td>Prepare 8 mg/ml stock solution in DMSO. Use at final concentration of 8 &#181;g/ml.</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dry bath</td>
			<td>Sheldon Manufacturing, Inc.</td>
			<td>52120-200</td>
			<td></td>
		</tr>
		<tr>
			<td>Metallic thermal beads</td>
			<td>Lab Armor</td>
			<td>42370-002</td>
			<td></td>
		</tr>
		<tr>
			<td>Epifluorescence microscope equipped with an EMCDD camera</td>
			<td></td>
			<td></td>
			<td>Nikon Eclipse TiE equipped with a QImaging Rolera em-c2 1K electron-multiplying charge-coupled-device (EMCCD) camera is used in this work.</td>
		</tr>
	</tbody>
</table>

live cell fluorescence microscopy to observe essential processes during microbial cell growth

Core cellular processes such as DNA replication and segregation, protein synthesis, cell wall biosynthesis, and cell division rely on the function of proteins which are essential for bacterial survival. A series of target-specific dyes can be used as probes to better understand these processes. Staining with lipophilic dyes enables the observation of membrane structure, visualization of lipid microdomains, and detection of membrane blebs. Use of fluorescent-d-amino acids (FDAAs) to probe the sites of peptidoglycan biosynthesis can indicate potential defects in cell wall biogenesis or cell growth patterning. Finally, nucleic acid stains can indicate possible defects in DNA replication or chromosome segregation. Cyanine DNA stains label living cells and are suitable for time-lapse microscopy enabling real-time observations of nucleoid morphology during cell growth. Protocols for cell labeling can be applied to protein depletion mutants to identify defects in membrane structure, cell wall biogenesis, or chromosome segregation. Furthermore, time-lapse microscopy can be used to monitor morphological changes as an essential protein is removed and can provide additional insights into protein function. For example, the depletion of essential cell division proteins results in filamentation or branching, whereas the depletion of cell growth proteins may cause cells to become shorter or rounder. Here, protocols for cell growth, target-specific labeling, and time-lapse microscopy are provided for the bacterial plant pathogen Agrobacterium tumefaciens. Together, target-specific dyes and time-lapse microscopy enable characterization of essential processes in A. tumefaciens. Finally, the protocols provided can be readily modified to probe essential processes in other bacteria.

Target-specific labeling of wildtype A. tumefaciens cells 
In order to illustrate that cell morphology is not impacted by the wash steps or treatment with 1% DMSO (which is used to dilute the fluorescent dyes), cells were imaged directly from culture (Figure 2A, far left panel), after washing the cells by centrifugation as described in 1.2 (Figure 2A, left panel), o...

Watch this Scientific Journal Video about Live Cell Fluorescence Microscopy to Observe Essential Processes During Microbial Cell Growth at JoVE.com

Live Cell Fluorescence Microscopy to Observe Essential Processes During Microbial Cell Growth

Understanding the function of essential processes in bacteria is challenging. Fluorescence microscopy with target-specific dyes can provide key insights into microbial cell growth and cell cycle progression. Here, Agrobacterium tumefaciens is used as a model bacterium to highlight methods for live cell imaging for characterization of essential processes.

Core cellular processes such as DNA replication and segregation, protein synthesis, cell wall biosynthesis, and cell division rely on the function of ...

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