This research was supported by NIH Grant AG043080 and the National Natural Science Foundation of China (NSFC), No. 11434001. We thank Lucas Waldburger for proofreading the manuscript.

1. Silicon Wafer Mold Fabrication
NOTE: The photomask is designed with AutoCAD software and manufactured by a commercial company. This design contains three layers of different patterns (<a href="http://cloudfront.jove.com/files/ftp_upload/55412/single_cell_trap.dwg" target="_blank">Supplementary File 1</a>). The heights of the first, second, and third layers are about 4 &#181;m, 10 &#181;m, and 50 &#181;m, respectively. The silicon wafer mold was created from the photomask using soft lithography9,10.
<ol>
	<li>Bake a silicon wafer at 200 &#176;C for 10 min to evaporate the water vapor. Spin coat negative photoresist SU-8 onto the silicon wafer. 
	NOTE: Spin coat SU-8 3005 at 5,000 rpm for 30 s to generate the first layer, SU-8 2010 at 3,000 rpm for 30 s to generate the second layer, and SU-8 3025 at 2,000 rpm for 30 s to generate the third layer.</li>
	<li>Soft-bake the coated wafer before the pattern transfer. Align and expose the wafer in &#34;direct contact&#34; mode using a mask aligner. 
	NOTE: Soft-bake the wafer for 2 min at 95 &#176;C for the first layer, 3 min at 95 &#176;C for the second layer, and 15 min at 95 &#176;C for the third layer. Use the exposure dose at 100 mJ/cm2 for the first layer, 130 mJ/cm2 for the second layer, and 200 mJ/cm2 for the third layer.</li>
	<li>After exposure, post-bake the wafer and develop it using SU-8 developer. Dry the wafer using an N2 gun and hard-bake the wafer at 200 &#176;C for 30 min. 
	NOTE: The silicon wafer mold is fixed to a 15 cm-diameter plastic Petri dish using scotch tape, with the pattern side facing up. Usually, we put several identical chip structures on the same mold, which allows multiple microfluidic chips to be fabricated at the same time. Each mold can be re-used many times to fabricate microfluidic chips.</li>
</ol>
2. Microfluidic Chip Fabrication
<ol>
	<li>Place a clean weighing boat on a balance and tare the balance. Pour 50 g of PDMS base into the weigh boat.</li>
	<li>Add 5 g of PDMS curing agent to the weigh boat (w/w ratio of 1:10 to the PDMS base). 
	NOTE: This volume is based on a 15 cm-diameter Petri dish with the mold. Adjust the amount of reagent if using a Petri dish of a different size.</li>
	<li>Stir the PDMS base and the curing agent with a disposable pipette. Start from the edge of the weighing boat and slowly move inwards. Stir thoroughly for several minutes until small bubbles form throughout the mixture; thorough mixing is essential for PDMS polymerization.</li>
	<li>Pour the mixture slowly into the Petri dish; the mixture must completely cover the silicon wafer mold.</li>
	<li>Place the Petri dish in a vacuum for 10 min to remove all the air bubbles from the PDMS mixture. If bubbles remain on the surface of the mixture, use a pipette to blow them out.</li>
	<li>Incubate the silicon wafer mold with PDMS in an oven at 75 &#176;C for about 2 h.</li>
	<li>Gently peel the layer of polymerized PDMS off the silicon wafer mold, avoiding any damage to the construction of the wafer mold. Alternatively, cut the PDMS directly from the silicon wafer mold with a minimum 5-mm margin around the pattern using a single-edge industrial razor blade; gently peel the PDMS layer off the wafer mold.</li>
	<li>Place the PDMS layer on the bench with the pattern side facing up. Carefully cut out the individual chip with a single-edge industrial razor blade, retaining an adequate margin from the edge of each single chip to avoid construction damage.</li>
	<li>With the pattern side facing up, use a punch pen (0.75-mm I.D.) to punch holes straight down through the inlet and outlet circles on each side of the channels. 
	NOTE: These holes create the pathway for the flow of medium. Therefore, it is crucial to go through the circles and punch all the way through the PDMS layer. Make sure to remove the PDMS columns from the hole.</li>
	<li>Check every punched hole by inserting the punch pen needle again into the hole. Make sure the needle can come out from the other side, indicating that there is no blockage. Apply tape to the pattern surface, then gently peel off the tape to clean dust particles. Repeat this step at least three times. Leave a clean piece of scotch tape on the PDMS to maintain sterilization.</li>
	<li>Repeat this procedure on the opposite side of the PDMS and leave the last piece of tape on as well.</li>
	<li>Prepare a 24 mm x 30 mm cover glass with a thickness of 0.13-0.17 mm. Spray 70% ethanol on the glass and dry with dust remover to sterilize the surface; additionally, the glass can be washed with autoclaved water and dried with dust remover.</li>
	<li>Transfer the cover glass and PDMS to a plastic plate. Remove the scotch tape from the PDMS and place the pattern side facing up. Avoid any contact with the pattern surface during the transfer.</li>
	<li>Place the plastic plate in the plasma machine. Apply oxygen plasma treatment to the PDMS and the cover glass to render the surfaces hydrophilic with the following operation parameters: exposure, 75 s; gas stabilization, 20 cc/min; pressure, 200; and power, 100 W.</li>
	<li>Carefully place the PDMS onto the cover glass, connecting both hydrophilic surfaces (the surfaces that faced up during the plasma treatment). Make sure that there are no air bubbles between the PDMS and the cover glass.</li>
	<li>Incubate the PDMS chip in an oven at 75 &#176;C for at least 2 h. 
	&#8203;NOTE: Deficient microfluidics may cause liquid leakage onto the microscope during the experiment. Therefore, it is important to check the bond between the PDMS and the cover glass by slightly lifting the PDMS from the edges with tweezers. Gently lifting the PDMS should not separate it from the cover glass, indicating a successful bond.</li>
</ol>
3. Preparing for the Experiment
<ol>
	<li>Tube preparation.
	<ol>
		<li>Submerge the input and output tubes in 70% ethanol solution separately 1 day before PDMS chip preparation.</li>
		<li>Fill a 5-mL syringe with autoclaved water to wash the tubes. Wash each tube by plugging the tube on the syringe and flushing the tube with water.</li>
		<li>Repeat the washing step at least 3 times to clean ethanol residue.</li>
	</ol>
	</li>
	<li>Examine the PDMS channels under an optical microscope with a 10X objective to make sure the structure is consistent and intact. Stabilize the PDMS chip onto the microscope platform using scotch tape. 
	NOTE: Make multiple chips at one time in step 2 to ensure that there are backup chips, especially if making the device for the first time.</li>
	<li>Fill a 5-mL syringe with autoclaved water. Secure the syringe to a syringe pump and insert the corresponding input and output tubes. Set the washing speed to 750 &#181;L/h to rinse the chip for about 10 min. The air bubbles on the branch channels should be washed away during this period; if there are remaining bubbles, manually adjust the speed to eliminate the bubbles.</li>
	<li>Yeast sample preparation.
	<ol>
		<li>Transfer 1 mL of prepared yeast sample (OD600 0.6-0.8) into two 1.5-mL microcentrifuge tubes and centrifuge for 5 min at 3,000 x g.</li>
		<li>Remove the majority of the supernatant from each tube and combine the remainder to form a 0.5-mL sample.</li>
	</ol>
	</li>
	<li>Pause the syringe pump and remove the input tubes from the PDMS chip.</li>
	<li>Manually reverse the syringe pump to suck a small air bubble (1 to 2 cm in length) into each input tube. Move on to suck in the yeast sample; the air bubble will show the sample boundary and indicate how much sample has been drawn. 
	NOTE: Avoid sucking the sample into the syringe.</li>
	<li>Insert the input tube back into the PDMS chip and restart the pump to load the cells at a speed of 750 &#181;L/h.</li>
	<li>Leave the syringe pump on for 10 min then and examine the cell loading progression under the microscope; a successful loading will trap cells under more than 60% of suspend pillar.</li>
	<li>Switch to nutrition solution and adjust the speed to 400 &#181;L/h for cell culturing.</li>
	<li>Select observation positions for the microscope. 
	NOTE: For lifespan measurements, images were taken once every 15 min by an optical microscope with a 40x objective. For the fluorescent reporter analysis, images were taken once every 15 min by a fluorescence microscope with a 60X oil objective.</li>
</ol>

<ol><li>Mortimer, R. K., Johnston, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Life+span+of+individual+yeast+cells%5BTitle%5D)+AND+%22Nature%22%5BJournal%5D)">Life span of individual yeast cells.</a> Nature. 183 (4677), 1751-1752 (1959).</li>
<li>Polymenis, M., Kennedy, B. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Cell+biology%3A+High-tech+yeast+ageing%5BTitle%5D)+AND+%22Nature%22%5BJournal%5D)">Cell biology: High-tech yeast ageing.</a> Nature. 486 (7401), 37-38 (2012).</li>
<li>Xie, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Molecular+phenotyping+of+aging+in+single+yeast+cells+using+a+novel+microfluidic+device%5BTitle%5D)+AND+%22Aging+Cell%22%5BJournal%5D)">Molecular phenotyping of aging in single yeast cells using a novel microfluidic device.</a> Aging Cell. 11 (4), 599-606 (2012).</li>
<li>Zhang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Single+cell+analysis+of+yeast+replicative+aging+using+a+new+generation+of+microfluidic+device%5BTitle%5D)+AND+%22PLoS+One%22%5BJournal%5D)">Single cell analysis of yeast replicative aging using a new generation of microfluidic device.</a> PLoS One. 7 (11), e48275(2012).</li>
<li>Chen, K. L., Crane, M. M., Kaeberlein, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microfluidic+technologies+for+yeast+replicative+lifespan+studies%5BTitle%5D)+AND+%22Mech+Ageing+Dev%22%5BJournal%5D)">Microfluidic technologies for yeast replicative lifespan studies.</a> Mech Ageing Dev. , (2016).</li>
<li>Lee, S. S., Avalos Vizcarra,, Huberts, I., H, D., Lee, L. P., Heinemann, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Whole+lifespan+microscopic+observation+of+budding+yeast+aging+through+a+microfluidic+dissection+platform%5BTitle%5D)+AND+%22Proc+Natl+Acad+Sci+U+S+A%22%5BJournal%5D)">Whole lifespan microscopic observation of budding yeast aging through a microfluidic dissection platform.</a> Proc Natl Acad Sci U S A. 109 (13), 4916-4920 (2012).</li>
<li>Huberts, D. H., Janssens, G. E., Lee, S. S., Vizcarra, I. A., Heinemann, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Continuous+high-resolution+microscopic+observation+of+replicative+aging+in+budding+yeast%5BTitle%5D)+AND+%22J+Vis+Exp%22%5BJournal%5D)">Continuous high-resolution microscopic observation of replicative aging in budding yeast.</a> J Vis Exp. (78), e50143(2013).</li>
<li>Jo, M. C., Liu, W., Gu, L., Dang, W., Qin, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((High-throughput+analysis+of+yeast+replicative+aging+using+a+microfluidic+system%5BTitle%5D)+AND+%22Proc+Natl+Acad+Sci+U+S+A%22%5BJournal%5D)">High-throughput analysis of yeast replicative aging using a microfluidic system.</a> Proc Natl Acad Sci U S A. 112 (30), 9364-9369 (2015).</li>
<li>Mata, A., Fleischman, A. J., Roy, S. <a target="_blank" href="http://iopscience.iop.org/article/10.1088/0960-1317/16/2/012/meta">Fabrication of multi-layer SU-8 microstructures.</a> Journal of Micromechanics and Microengineering. 16 (2), 276-284 (2006).</li>
<li>Xia, Y. N., Whitesides, G. M. <a target="_blank" href="http://www.annualreviews.org/doi/abs/10.1146/annurev.matsci.28.1.153">Soft lithography.</a> Angewandte Chemie-International Edition. 37 (5), 550-575 (1998).</li>
<li>Schneider, C. A., Rasband, W. S., Eliceiri, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((NIH+Image+to+ImageJ%3A+25+years+of+image+analysis%5BTitle%5D)+AND+%22Nat+Methods%22%5BJournal%5D)">NIH Image to ImageJ: 25 years of image analysis.</a> Nat Methods. 9 (7), 671-675 (2012).</li>
<li>Xie, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Early+telomerase+inactivation+accelerates+aging+independently+of+telomere+length%5BTitle%5D)+AND+%22Cell%22%5BJournal%5D)">Early telomerase inactivation accelerates aging independently of telomere length.</a> Cell. 160 (5), 928-939 (2015).</li>
<li>Boy-Marcotte, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+heat+shock+response+in+yeast%3A+differential+regulations+and+contributions+of+the+Msn2p%2FMsn4p+and+Hsf1p+regulons%5BTitle%5D)+AND+%22Mol+Microbiol%22%5BJournal%5D)">The heat shock response in yeast: differential regulations and contributions of the Msn2p/Msn4p and Hsf1p regulons.</a> Mol Microbiol. 33 (2), 274-283 (1999).</li>
<li>Yang, X., Lau, K. Y., Sevim, V., Tang, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Design+principles+of+the+yeast+G1%2FS+switch%5BTitle%5D)+AND+%22PLoS+Biol%22%5BJournal%5D)">Design principles of the yeast G1/S switch.</a> PLoS Biol. 11 (10), e1001673(2013).</li>
</ol>

The authors declare that they have no competing financial interests.

The PDMS device needs to be freshly made. Otherwise, the air bubbles caused by inserting tubes into the device will be difficult to remove. Step 3.4 is important to improve the cell loading efficiency by concentrating the cells. To increase the throughput of the experiment, 4 to 6 modules on the same PDMS chip connected to independently operating pumps are typically used to perform 4 to 6 different experiments (different strains or media compositions) simultaneously.
Compared to the convention...

Budding yeast is a powerful model organism in aging research. However, a conventional lifespan assay in yeast relies on microdissection, which is not only labor intensive but also low throughput1,2. In addition, the traditional microdissection approach does not provide a detailed view of various cellular and molecular features in the single mother cells as they age. The development of microfluidic devices has enabled an automated procedure to measure yeast lifespan as well as to follow molecular markers and various cellular phenotypes throughout the lifespan of the mother cells3,4,5,6,7,8. After yeast cells are loaded into a microfluidic device, they can be tracked under a microscope using automatic time-lapse imaging. With the help of imaging processing tools, various cellular and molecular phenotypes can be extracted3,6,8, including lifespan, size, fluorescent reporter, cell morphology, cell cycle dynamics, etc., many of which are difficult or impossible to obtain using the traditional microdissection method. Microfluidic devices have gained prominence in yeast aging research since their successful development a few years ago3,4,6,7. Several groups have subsequently published on variations of the earlier designs5, and many yeast labs have employed microfluidic devices for their study.
In a cell culture undergoing exponential growth, the number of aged mother cells that are available for observation is miniscule. Therefore, the general design principle of the microfluidic device for lifespan measurements is to retain mother cells and to remove daughter cells. One such designs makes use of the fact that yeast undergoes asymmetric cell division. The structures in the device will trap bigger mother cells and allow smaller daughter cells to be washed away. The microfluidic chip described in this article uses a soft polydimethylsiloxane (PDMS) pad (vertical pensile columns) to trap mother cells (Figure 1). Devices of similar design have been reported previously3,4,6,7. This protocol uses a simpler procedure to fabricate microfluidic devices and a straightforward cell-loading method that is optimized for the time-lapse imaging experiments. One of the key parameters in the microfluidic device is the width of the PDMS pads used to trap mother cells. Our device uses wider pads that can keep more mother cells under each pad, including a significant fraction of fresh mother cells that can be tracked throughout their lifespan. In addition to lifespan measurements, this protocol is useful for single cell time-lapse imaging experiments when the cells need to be tracked for many generations or when an observation throughout the entire lifespan is necessary.

<table><tbody><tr><td>3&#039;&#039; &amp;lt;111&gt; silicon wafer</td><td>Addison Engineering</td><td></td><td></td></tr><tr><td>SU-8 2000 and 3000 Series</td><td>MicroChem</td><td></td><td></td></tr><tr><td>Sylgard&amp;reg; 184 Silicone Elastomer Kit</td><td>ellsworth</td><td>2065622</td><td>Include Sylgard&amp;reg; silicone elastomer base and curing agent</td></tr><tr><td>Petri dishes</td><td>VWR</td><td>391-1502</td><td></td></tr><tr><td>Harris Uni-core&amp;trade; punch (I.D. 0.75 mm)</td><td>Sigma-Aldrich</td><td>29002513</td><td></td></tr><tr><td>24 mm x 40 mm SLIP-RITE&amp;reg; cover glass</td><td>Thermo Fisher Scientific</td><td>102440</td><td></td></tr><tr><td>3M Scotch Tape</td><td>ULINE</td><td>S-10223</td><td></td></tr><tr><td>VWR&amp;reg; Razor Blades</td><td>VWR</td><td>55411-050</td><td></td></tr><tr><td>Pure Ethanol, Koptec</td><td>VWR</td><td>64-17-5</td><td></td></tr><tr><td>Whoosh-Duster&amp;trade;</td><td>VWR</td><td>16650-027</td><td></td></tr><tr><td>5 mL BD Syringe (Luer-Lock&amp;trade; Tip)</td><td>Becton, Dickinson and Company</td><td>309646</td><td></td></tr><tr><td>PTFE Standard Wall Tubing (100 ft, AWG Size: 22, Nominal ID: 0.028)</td><td>Component Supply Company</td><td>SWTT-22</td><td></td></tr><tr><td>Needle Assortment</td><td>Component Supply Company</td><td>NEKIT-1</td><td></td></tr><tr><td>Desiccator</td><td>HACH</td><td>2238300</td><td></td></tr><tr><td>Lab Oven</td><td>Fisher Scientific</td><td>13246516GAQ</td><td></td></tr><tr><td>Nikon TE2000 microscope with 40X and 60X objective</td><td>Nikon</td><td></td><td></td></tr><tr><td>Zeiss Axio Observer Z1 with 40X and 60X objective</td><td>Zeiss</td><td></td><td></td></tr><tr><td>Syringe Pump</td><td>Longerpump</td><td>TS-1B</td><td></td></tr></tbody></table>

using microfluidic devices to measure lifespan and cellular phenotypes in single budding yeast cells

Budding yeast Saccharomyces cerevisiae is an important model organism in aging research. Genetic studies have revealed many genes with conserved effects on the lifespan across species. However, the molecular causes of aging and death remain elusive. To gain a systematic understanding of the molecular mechanisms underlying yeast aging, we need high-throughput methods to measure lifespan and to quantify various cellular and molecular phenotypes in single cells. Previously, we developed microfluidic devices to track budding yeast mother cells throughout their lifespan while flushing away newborn daughter cells. This article presents a method for preparing microfluidic chips and for setting up microfluidic experiments. Multiple channels can be used to simultaneously track cells under different conditions or from different yeast strains. A typical setup can track hundreds of cells per channel and allow for high-resolution microscope imaging throughout the lifespan of the cells. Our method also allows detailed characterization of the lifespan, molecular markers, cell morphology, and the cell cycle dynamics of single cells. In addition, our microfluidic device is able to trap a significant amount of fresh mother cells that can be identified by downstream image analysis, making it possible to measure the lifespan with higher accuracy.

After the experiments, the lifespans of the cells and many cellular and molecular phenotypes can be extracted from the recorded time-lapse images. Since there are a number of different features that can be extracted from each cell, the first step of the analysis is to annotate the cells and events, including the positions and boundaries of the cells and the timing of various events that are being tracked, such as the budding events. These annotations will make it easier to return to the s...

Watch this Scientific Journal Video about Using Microfluidic Devices to Measure Lifespan and Cellular Phenotypes in Single Budding Yeast Cells at JoVE.com

Using Microfluidic Devices to Measure Lifespan and Cellular Phenotypes in Single Budding Yeast Cells

This article presents a protocol optimized for the production of microfluidic chips and the setup of microfluidic experiments to measure the lifespan and cellular phenotypes of single yeast cells.

Budding yeast Saccharomyces cerevisiae is an important model organism in aging research. Genetic studies have revealed many genes with conserved effects ...

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JoVE Journal

Biology

7.7K Views.  Peking University.  Dit artikel een protocol geoptimaliseerd voor het vervaardigen van microfluïdische chips en de opstelling van microfluïdische experimenten om de levensduur en cellulaire fenotypen van afzonderlijke gistcellen te meten. 

Video: Using Microfluidic Devices to Measure Lifespan and Cellular Phenotypes in Single Budding Yeast Cells

A Microfluidic Device for Studying Multiple Distinct Strains

The study of cell responses to environmental changes poses many experimental challenges: cells need to be imaged under changing conditions, often in a comparative manner. Multiwell plates are routinely used to compare many different strains or cell lines, but allow limited control over the environment dynamics. Microfluidic devices, on the other hand, allow exquisite dynamic control over the surrounding conditions, but it is challenging to image and distinguish more than a few strains in them. Here we describe a method to easily and rapidly manufacture a microfluidic device capable of applying dynamically changing conditions to multiple distinct yeast strains in one channel. The device is designed and manufactured by simple means without the need for soft lithography. It is composed of a Y-shaped flow channel attached to a second layer harboring microwells. The strains are placed in separate microwells, and imaged under the exact same dynamic conditions. We demonstrate the use of the device for measuring protein localization responses to pulses of nutrient changes in different yeast strains.

We present a simple method to produce microfluidic devices capable of applying similar dynamic conditions to multiple distinct strains, without the need for a clean room or soft lithography.

The study of cell responses to environmental changes poses many experimental challenges: cells need to be imaged under changing conditions, often in a ...

Bioengineering

Continuous High-resolution Microscopic Observation of Replicative Aging in Budding Yeast

We demonstrate the use of a simple microfluidic setup, in which single budding yeast cells can be tracked throughout their entire lifespan. The microfluidic chip exploits the size difference between mother and daughter cells using an array of micropads. Upon loading, cells are trapped underneath these micropads, because the distance between the micropad and cover glass is similar to the diameter of a yeast cell (3-4 &mu;m). After the loading procedure, culture medium is continuously flushed through the chip, which not only creates a constant and defined environment throughout the entire experiment, but also flushes out the emerging daughter cells, which are not retained underneath the pads due to their smaller size. The setup retains mother cells so efficiently that in a single experiment up to 50 individual cells can be monitored in a fully automated manner for 5 days or, if necessary, longer. In addition, the excellent optical properties of the chip allow high-resolution imaging of cells during the entire aging process.

We describe here the operation of a microfluidic device that allows continuous and high-resolution microscopic imaging of single budding yeast cells during their complete replicative and/or chronological lifespan.

We demonstrate the use of a simple microfluidic setup, in which single budding yeast cells can be tracked throughout their entire lifespan. The ...

Microfluidic Picoliter Bioreactor for Microbial Single-cell Analysis: Fabrication, System Setup, and Operation

In this protocol the fabrication, experimental setup and basic operation of the recently introduced microfluidic picoliter bioreactor (PLBR) is described in detail. The PLBR can be utilized for the analysis of single bacteria and microcolonies to investigate biotechnological and microbiological related questions concerning, e.g.&#160;cell growth, morphology, stress response, and metabolite or protein production on single-cell level. The device features continuous media flow enabling constant environmental conditions for perturbation studies, but in addition allows fast medium changes as well as oscillating conditions to mimic any desired environmental situation. To fabricate the single use devices, a silicon wafer containing sub micrometer sized SU-8 structures served as the replication mold for rapid polydimethylsiloxane casting. Chips were cut, assembled, connected, and set up onto a high resolution and fully automated microscope suited for time-lapse imaging, a powerful tool for spatio-temporal cell analysis. Here, the biotechnological platform organism Corynebacterium glutamicum&#160;was seeded into the PLBR and cell growth and intracellular fluorescence were followed over several hours unraveling time dependent population heterogeneity on single-cell level, not possible with conventional analysis methods such as flow cytometry. Besides insights into device fabrication, furthermore, the preparation of the preculture, loading, trapping of bacteria, and the PLBR cultivation of single cells and colonies is demonstrated. These devices will add a new dimension in microbiological research to analyze time dependent phenomena of single bacteria under tight environmental control. Due to the simple and relatively short fabrication process the technology can be easily adapted at any microfluidics lab and simply tailored towards specific needs.

In this protocol the fabrication, setup and basic operation of a microfluidic picoliter bioreactor (PLBR) for single-cell analysis of prokaryotic microorganisms is introduced. Industrially relevant microorganisms were analyzed as proof of principle allowing insights into growth rate, morphology, and phenotypic heterogeneity over certain time periods, hardly possible with conventional methods.

In this protocol the fabrication, experimental setup and basic operation of the recently introduced microfluidic picoliter bioreactor (PLBR) is described ...

Quantifying Yeast Chronological Life Span by Outgrowth of Aged Cells

The budding yeast Saccharomyces cerevisiae has proven to be an important model organism in the field of aging research 1. The replicative and chronological life spans are two established paradigms used to study aging in yeast. Replicative aging is defined as the number of daughter cells a single yeast mother cell produces before senescence; chronological aging is defined by the length of time cells can survive in a non-dividing, quiescence-like state 2. We have developed a high-throughput method for quantitative measurement of chronological life span. This method involves aging the cells in a defined medium under agitation and at constant temperature. At each age-point, a sub-population of cells is removed from the aging culture and inoculated into rich growth medium. A high-resolution growth curve is then obtained for this sub-population of aged cells using a Bioscreen C MBR machine. An algorithm is then applied to determine the relative proportion of viable cells in each sub-population based on the growth kinetics at each age-point. This method requires substantially less time and resources compared to other chronological lifespan assays while maintaining reproducibility and precision. The high-throughput nature of this assay should allow for large-scale genetic and chemical screens to identify novel longevity modifiers for further testing in more complex organisms.

Chronological aging in yeast refers to the loss of cell viability associated with time in stationary phase. Here we describe a high-throughput method for quantitatively determining yeast chronological life span.

The budding yeast Saccharomyces cerevisiae has proven to be an important model organism in the field of aging research 1. The replicative and ...

Measuring Replicative Life Span in the Budding Yeast

Aging is a degenerative process characterized by a progressive deterioration of cellular components and organelles resulting in mortality. The budding yeast Saccharomyces cerevisiae has been used extensively to study the biology of aging, and several determinants of yeast longevity have been shown to be conserved in multicellular eukaryotes, including worms, flies, and mice 1. Due to the lack of easily quantified age-associated phenotypes, aging in yeast has been assayed almost exclusively by measuring the life span of cells in different contexts, with two different life span paradigms in common usage 2. Chronological life span refers to the length of time that a mother cell can survive in a non-dividing, quiescence-like state, and is proposed to serve as a model for aging of post-mitotic cells in multicellular eukaryotes. Replicative life span, in contrast, refers the number of daughter cells produced by a mother cell prior to senescence, and is thought to provide a model of aging in mitotically active cells. Here we present a generalized protocol for measuring the replicative life span of budding yeast mother cells. The goal of the replicative life span assay is to determine how many times each mother cell buds. The mother and daughter cells can be easily differentiated by an experienced researcher using a standard light microscope (total magnification 160X), such as the Zeiss Axioscope 40 or another comparable model. Physical separation of daughter cells from mother cells is achieved using a manual micromanipulator equipped with a fiber-optic needle. Typical laboratory yeast strains produce 20-30 daughter cells per mother and one life span experiment requires 2-3 weeks.

In this article we present a general protocol for measuring the replicative life span of yeast mother cells.

Aging is a degenerative process characterized by a progressive deterioration of cellular components and organelles resulting in mortality. The budding ...

A Suppressor Screen for the Characterization of Genetic Links Regulating Chronological Lifespan in Saccharomyces cerevisiae

Aging is the time dependent deterioration of an organism&#8217;s normal biological processes that increases the probability of death. Many genetic factors contribute to alterations in the normal aging process. These factors intersect in complex ways, as evidenced by the wealth of documented links identified and conserved in many organisms. Most of these studies focus on loss-of-function, null mutants that allow for rapid screening of many genes simultaneously. There is much less work that focuses on characterizing the role that overexpression of a gene in this process. In the present work, we present a straightforward methodology to identify and clone genes in the budding yeast, Saccharomyces cerevisiae, for study in suppression of the short-lived chronological lifespan phenotype seen in many genetic backgrounds. This protocol is designed to be accessible to researchers from a wide variety of backgrounds and at various academic stages. The SIR2 gene, which codes for a histone deacetylase, was selected for cloning in the pRS315 vector, as there have been conflicting reports on its effect on the chronological lifespan. SIR2 also plays a role in autophagy, which results when disrupted via the deletion of several genes, including the transcription factor ATG1. As a proof of principle, we clone the SIR2 gene to perform a suppressor screen on the shortened lifespan phenotype characteristic of the autophagy deficient atg1&#916; mutant and compare it to an otherwise isogenic, wild type genetic background.

A Suppressor Screen for the Characterization of Genetic Links Regulating Chronological Lifespan in Saccharomyces cerevisiae

Here is a protocol to identify genetic interactions through an increased copy number suppressor screen in Saccharomyces cerevisiae. This method allows researchers to identify, clone, and test suppressors in short-lived yeast mutants. We test the effect of the copy number increase of SIR2 on lifespan in an autophagy null mutant.

Aging is the time dependent deterioration of an organism&#8217;s normal biological processes that increases the probability of death. Many genetic factors ...

Genetics

Studying Age-dependent Genomic Instability using the S. cerevisiae Chronological Lifespan Model

Studies using the Saccharomyces cerevisiae aging model have uncovered life span regulatory pathways that are partially conserved in higher eukaryotes1-2. The simplicity and power of the yeast aging model can also be explored to study DNA damage and genome maintenance as well as their contributions to diseases during aging. Here, we describe a system to study age-dependent DNA mutations, including base substitutions, frame-shift mutations, gross chromosomal rearrangements, and homologous/homeologous recombination, as well as nuclear DNA repair activity by combining the yeast chronological life span with simple DNA damage and mutation assays. The methods described here should facilitate the identification of genes/pathways that regulate genomic instability and the mechanisms that underlie age-dependent DNA mutations and cancer in mammals.

Studying Age-dependent Genomic Instability using the S. cerevisiae Chronological Lifespan Model

Here we describe a set of DNA mutation assays that can be combined with the yeast chronological life span model to study the genes/pathways that regulate or contribute to genomic DNA instability during aging.

Studies using the Saccharomyces cerevisiae aging model have uncovered life span regulatory pathways that are partially conserved in higher eukaryotes1-2. ...

Acquiring Fluorescence Time-lapse Movies of Budding Yeast and Analyzing Single-cell Dynamics using GRAFTS

Fluorescence time-lapse microscopy has become a powerful tool in the study of many biological processes at the single-cell level. In particular, movies depicting the temporal dependence of gene expression provide insight into the dynamics of its regulation; however, there are many technical challenges to obtaining and analyzing fluorescence movies of single cells. We describe here a simple protocol using a commercially available microfluidic culture device to generate such data, and a MATLAB-based, graphical user interface (GUI) -based software package to quantify the fluorescence images. The software segments and tracks cells, enables the user to visually curate errors in the data, and automatically assigns lineage and division times. The GUI further analyzes the time series to produce whole cell traces as well as their first and second time derivatives. While the software was designed for S. cerevisiae, its modularity and versatility should allow it to serve as a platform for studying other cell types with few modifications.

We present a simple protocol to obtain fluorescence microscopy movies of growing yeast cells, and a GUI-based software package to extract single-cell time series data. The analysis includes automated lineage and division time assignment integrated with visual inspection and manual curation of tracked data.

Fluorescence time-lapse microscopy has become a powerful tool in the study of many biological processes at the single-cell level. In particular, movies ...

ODELAY: A Large-scale Method for Multi-parameter Quantification of Yeast Growth

Growth phenotypes of microorganisms are a strong indicator of their underlying genetic fitness and can be segregated into 3 growth regimes: lag-phase, log-phase, and stationary-phase. Each growth phase can reveal different aspects of fitness that are related to various environmental and genetic conditions. High-resolution and quantitative measurements of all 3 phases of growth are generally difficult to obtain. Here we present a detailed method to characterize all 3 growth phases on solid media using an assay called One-cell Doubling Evaluation of Living Arrays of Yeast (ODELAY). ODELAY quantifies growth phenotypes of individual cells growing into colonies on solid media using time-lapse microscopy. This method can directly observe population heterogeneity with each growth parameter in genetically identical cells growing into colonies. This population heterogeneity offers a unique perspective for understanding genetic and epigenetic regulation, and responses to genetic and environmental perturbations. While the ODELAY method is demonstrated using yeast, it can be utilized on any colony forming microorganism that is visible by bright field microscopy.

We present a method for quantifying growth phenotypes of individual yeast cells as they grow into colonies on solid media using time-lapse microscopy termed, One-cell Doubling Evaluation of Living Arrays of Yeast (ODELAY). Population heterogeneity of genetically identical cells growing into colonies can be directly observed and quantified.

Growth phenotypes of microorganisms are a strong indicator of their underlying genetic fitness and can be segregated into 3 growth regimes: lag-phase, ...

Single-cell Microfluidic Analysis of Bacillus subtilis

Microfluidic technology overcomes many of the limitations to traditional analytical methods in microbiology. Unlike bulk-culture methods, it offers single-cell resolution and long observation times spanning hundreds of generations; unlike agarose pad-based microscopy, it has uniform growth conditions that can be tightly controlled. Because the continuous flow of growth medium isolates the cells in a microfluidic device from unpredictable variations in the local chemical environment caused by cell growth and metabolism, authentic changes in gene expression and cell growth in response to specific stimuli can be more confidently observed. Bacillus subtilis is used here as a model bacterial species to demonstrate a &#34;mother machine&#34;-type method for cellular analysis. We show how to construct and plumb a microfluidic device, load it with cells, initiate microscopic imaging, and expose cells to a stimulus by switching from one growth medium to another. A stress-responsive reporter is used as an example to reveal the type of data that may be obtained by this method. We also briefly discuss further applications of this method for other types of experiments, such as analysis of bacterial sporulation.

Single-cell Microfluidic Analysis of Bacillus subtilis

We present a method for the microfluidic analysis of individual bacterial cell lineages using Bacillus subtilis as an example. The method overcomes shortcomings of traditional analytical methods in microbiology by allowing observation of hundreds of cell generations under tightly controllable and uniform growth conditions.

Microfluidic technology overcomes many of the limitations to traditional analytical methods in microbiology. Unlike bulk-culture methods, it offers ...

Using Microfluidic Devices to Measure Lifespan and Cellular Phenotypes in Single Budding Yeast Cells

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