Name: calcium chloride dna uptake in e. coli
Uploaded: 2023-04-30T07:10:31.000Z
Duration: 10 min 54 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.16

SC.912.L.16.7

transformation-e-coli-cells-using-an-adapted-calcium-chloride

Transformation of E. coli Cells Using an Adapted Calcium Chloride Procedure

This protocol describes the preparation and transformation of competent E. coli DH5α using an adaptation of the calcium chloride procedure (12).
1. Set-up
<ol>
	<li>Equipment
	<ul>
		<li>Spectrophotometer</li>
		<li>Sorval Centrifuge (or equivalent)</li>
		<li>Benchtop centrifuge</li>
		<li>Heat block or water bath</li>
		<li>Orbital Shaker</li>
		<li>Stationary Incubator</li>
		<li>Gel casting tray</li>
		<li>Well combs</li>
		<li>Voltage source</li>
		<li>Gel box</li>
		<li>UV light source</li>
		<li>Microwave</li>
	</ul>
	</li>
	<li>Solutions and reagents
	<ul>
		<li>Luria-Bertani (LB) broth (10 g casein enzymic hydrolysate, 5 g yeast extract and 5 g sodium chloride in 1000 mL of H2O)</li>
		<li>Super Optimal broth with Catabolite repression (SOC): (2% (w/v) tryptone, 0.5% (w/v) yeast extract, 10 mM NaCl, 2.5 mM KCl, 10 mM MgCl2, 10 mM MgSO4, and 20 mM glucose)</li>
		<li>CaCl2-MgCl2 (80 mM MgCl2, 20 mM CaCl2) solution.</li>
		<li>M CaCl2 solution (if cells will be transformed immediately) or 0.1M CaCl2 solution containing 10% (v/v) glycerol (if cells will be frozen for future use).</li>
		<li>LB agar plates</li>
		<li>LB agar selective plates (for this experiment, since the plasmid used confers ampicillin resistance, LB agar plates containing ampicillin 100 µg/mL were used)</li>
		<li>E. coli DH5α strain</li>
		<li>Plasmid pUC19 DNA (100 pg/ µl)</li>
		<li>QIAprep Spin Miniprep Kit (Qiagen)</li>
		<li>HindIII restriction enzyme</li>
		<li>1 kb plus DNA ladder</li>
		<li>Low Melting Point Agarose</li>
		<li>1X TAE buffer (40 mM Tris Base, 20 mM Acetic Acid and 1mM EDTA)</li>
		<li>Ethidium Bromide (10mg/mL)</li>
	</ul>
	</li>
	<li>General safety notes 
	E. coli DH5α is classified as Biosafety Level 1 (BSL1). Microbes in this category pose little to no threat of infection in healthy adults. However, careful manipulation of the microorganism is required.</li>
</ol>
IMPORTANT all steps in this protocol need to be carried out using aseptic techniques and on ice or 4°C temperatures unless indicated.
2. Protocol
<ol>
	<li>From a frozen stock of E. coli DH5α (frozen in 20% glycerol from an overnight culture grown in LB) streak out bacteria for isolation on an LB agar plate. Incubate at 37°C overnight (16-20 hours).</li>
	<li>Inoculate a single colony into 3 mL of LB broth in a tube. Grow shaking at 210 rpm at 37°C overnight (16-20 hours).</li>
	<li>Measure the OD600 of the overnight culture. Use the overnight culture to inoculate 100 mL of LB broth in a 1-liter flask to an OD600=0.01. Incubate the culture shaking vigorously (210 rpm) at 37°C monitoring OD600 in the spectrophotometer every 15-20 min, until culture reaches OD600=0.35 (approximately 3 hours). 
	NOTE: For transformation to be efficient, bacterial cells need to be at mid-exponential growth phase. The maximum number of cells needs to be 108 cells/mL, which for most strains of E. coli corresponds to OD600=0.4. The use of the spectrophotometer allows to measure the OD600, which allows to determine that the cells are at the appropriate growth stage. If this protocol will be used for other strains of bacteria, calibration to determine the number of colonies forming units at specific OD600 values will be necessary to determine this correlation.</li>
	<li>Transfer the 50 mL of the culture to each of 2 ice-cold polypropylene centrifuge bottles. Place the bottles on ice for 20 min to cool.</li>
	<li>Recover the cells by centrifugation at 2700g (4100 rpm in a Sorval GSA rotor) for 10 min at 4°C.</li>
	<li>Remove the supernatant. Drain away the last traces of media by placing the bottle upside down on a pad or paper towel.</li>
	<li>Resuspend each bacterial pellet into 30 mL of a CaCl2-MgCl2 (80 mM MgCl2, 20 mM CaCl2) ice-cold solution. First add 5 mL of the solution, swirl carefully until pellet has dissolved completely and then add the remaining 25 mL of solution.</li>
	<li>Repeat step 2.4.</li>
	<li>Repeat step 2.5.</li>
	<li>If competent cells are going to be directly transformed, resuspend each bacterial pellet into 2 mL of a CaCl2 (0.1 M) ice-cold solution by swirling the tubes carefully. If the pellet does not get resuspended with this method, resuspend by gently pipetting up and down (avoiding bubble formation). 
	Alternatively, the competent cells can be frozen and stored for later use. To prepare frozen stocks of competent cells, resuspend the pellet in 2 ml of a 0.1M CaCl2 solution containing 10% (v/v) glycerol. This solution needs to be ice-cold. Aliquot cell suspension into ice-cold 1.5 mL polypropylene tubes (160 µl per tube). Freeze competent cells immediately in a dry ice/ethanol bath. Transfer tubes to a -70°C freezer.</li>
	<li>To transform the CaCl2-treated cells, transfer 50 µl of competent cells to each of 2 1.5 ml polypropylene tubes. Add the 1 µl (100 pg) of pUC19 plasmid DNA to one of the tubes and leave the second tube without DNA (negative control). Mix gently (avoid bubble formation). Incubate for 30 min on ice. 
	NOTE: No more than 50 ng of DNA in a volume of 10 µL or less should be used in the transformation.</li>
	<li>Transfer the tubes to the heat block and incubate at 42°C for 45 s exactly. 
	NOTE: Heat shock is a critical step. Do not exceed temperature or incubation time.</li>
	<li>Readily transfer tubes to ice. Incubate for 2 min.</li>
	<li>Add 950 µL of SOC media and incubate the tubes for 1 hour at 37°C to allow the bacteria to recover and express the antibiotic resistant marker encoded in the plasmid.</li>
	<li>Dilute 10 µL of the cell suspension in 1000 µL in SOC (1/100 dilution) and 100 µL of the cell suspension in 1000 µL in SOC (1/10 dilution). Plate 100 µl of the dilutions, as well as the control, onto selective plates, and spread using a spatula. Usually, plating 100 µL of a 1/100 and 1/10 dilution will yield enough number of colony forming units (cfu) per plate. Ideally, this number should range between 30-300 cfu so that there are enough colonies but separated from each other. However, the number of cfu will depend on the transformation efficiency (see Data Analysis and Results Section).</li>
	<li>Incubate the plates at 37°C. Transformed colonies should appear in 12-16 hours (this range will depend on the cell strain and selection method). No colonies should grow in the negative control.</li>
	<li>Count the cfu/plate obtained for the transformation (Table 1).</li>
	<li>To verify the transformants harbor the pUC19 plasmid, a plasmid preparation and subsequent digestion will be performed. To this end, inoculate a single colony into 3 ml of LB broth in a tube. Grow shaking at 210 rpm at 37°C overnight (16-20 hours).</li>
	<li>Prepare a plasmid preparation using the QIAprep Spin Miniprep Kit, according to the instructions from the manufacturer.</li>
	<li>Digest the 1 µg of purified pUC19 with the restriction enzyme HindIII at 37°C for 1 hour. 
	NOTE: Any enzyme that cuts in the pUC19 multiple cloning site can be used for this step.</li>
</ol>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Component</td>
			<td>Amount</td>
		</tr>
		<tr>
			<td>10X Restriction digest buffer</td>
			<td>2.5 µl</td>
		</tr>
		<tr>
			<td>Plasmid pUC19</td>
			<td>1 µg</td>
		</tr>
		<tr>
			<td>HindIII</td>
			<td>1 µl</td>
		</tr>
		<tr>
			<td>H2O</td>
			<td>20.5 µl (to 25 µl)</td>
		</tr>
	</tbody>
</table>
<ol start="21">
	<li>Run a molecular weight ladder, digested pUC19 DNA and the same amount of undigested pUC19 DNA in a 1% agarose gel containing 1 µg/mL ethidium bromide for 1 hour at 95 V. 
	NOTE: time and voltage will vary depending on equipment used.</li>
	<li>Visualize gel under UV light. Compare size of digested and undigested pUC19 DNA (Figure 2) (see Data Analysis and Results Section). 
	Proceed with the necessary steps required to verify the transformation according to the goal of each particular transformation experiment.</li>
</ol>
<img alt="Electrophoresis gel diagram with DNA ladder, undigested and HindIII digested plasmid for size comparison." class="xfigimg" src="/files/ftp_upload/10515/10515fig2.jpg" data-altupdatedat="1761830439000" data-alt="Figure 2"> 
Figure 2: Digestion of recovered plasmid DNA from transformed DH5α cells. Plasmid DNA was recovered from transformed DH5α cells, digested with HindIII, run in a 1% agarose gel and visualized with a UV source (steps 2.19 to 2.22).
3. Data Analysis and Results
To calculate the transformation efficiency, an indicator of how well the cells took up the extracellular DNA, the colonies obtained in the transformation need to be counted:
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Dilution</td>
			<td>Cfu</td>
		</tr>
		<tr>
			<td>1/100</td>
			<td>34</td>
		</tr>
		<tr>
			<td>1/10</td>
			<td>246</td>
		</tr>
	</tbody>
</table>
Table 1: Colony forming units (cfu) counted from transformation experiment.
Transformation efficiency (TE) is a measure of the number of cfu resulting from transforming 1 µg of plasmid into a given volume of competent cells. Many parameters affect the transformation efficiency: plasmid size, cell genotype, growth stage during competence preparation, methods of transformation, etc.). When calculating the TE is important to consider what dilution (if any) was performed before plating and incorporate it in the calculation of the total number of cfu. The transformation efficiency (TE) is calculated with the following equation:
<img src="/files/ftp_upload/10515/10515eq1.jpg" alt="Transfection efficiency equation: TE=cfu/(DNA amount/μg) per dilution." data-altupdatedat="1761830439000">
First divide the cfu by the µg of DNA, in this example 0.0001µg. Then divide the result by the dilution factor. In this example, a 1/10 dilution was used and 100µL of a 1 ml solution was plated (dilution: 1/10 × 100 µL /1000 µL=0.01).
<img src="/files/ftp_upload/10515/10515eq2.jpg" alt="Transformation efficiency formula; equation showing CFU to DNA ratio, 2.46×10⁸ CFU/µg calculation." data-altupdatedat="1761830439000">

Transformation is a powerful method for introducing exogenous DNA into bacterial cells that is key to many molecular biology applications in the laboratory. Additionally, it plays a major role in nature by allowing bacterial cells to exchange genetic material that could result in increased genetic variation and allow for acquisition of different beneficial traits for survival under a wide range of conditions. Many bacterial strains encode the genes required for natural competence. However, the conditions in which these g...

transformation of e. coli cells using an adapted calcium chloride procedure

Source: Natalia Martin1, Andrew J. Van Alst1, Rhiannon M. LeVeque1, and Victor J. DiRita1 
1 Department of Microbiology and Molecular Genetics, Michigan State University
Bacteria have the ability to exchange genetic material (DeoxyriboNucleic Acid, DNA) in a process known as horizontal gene transfer. Incorporating exogenous DNA provides a mechanism by which bacteria can acquire new genetic traits that allow them to adapt to changing environmental conditions, such as the presence of antibiotics or antibodies (1) or molecules found in natural habitats (2). There are three mechanisms of horizontal gene transfer: transformation, transduction, and conjugation (3). Here we will focus on transformation, the ability of bacteria to take up free DNA from the environment. In the laboratory, the transformation process has four general steps: 1) Preparation of competent cells, 2) Incubation of competent cells with DNA, 3) Recovery of cells, and 4) Plating of the cells for growth of the transformants (Figure 1).
<img alt="Bacterial transformation process diagram with stages: cell preparation, transformation, recovery, plating." class="xfigimg" src="/files/ftp_upload/10515/10515fig1.jpg" data-altupdatedat="1761830439000" data-alt="Figure 1"> 
Figure 1: General steps of the transformation process. The transformation process has four general steps: 1) Preparation of competent cells, 2) Incubation with DNA, 3) Recovery of the cells and 4) Plating cells for growth of the transformants.
For transformation to occur, the recipient bacteria must be in a state known as competence. Some bacteria have the ability to become naturally competent in response to certain environmental conditions. However, many other bacteria do not become competent naturally, or the conditions for this process are yet unknown. The ability to introduce DNA into bacteria has a range of research applications: to generate multiple copies of a DNA molecule of interest, to express large amount of proteins, as a component in cloning procedures, and others. Because of the value of transformation to molecular biology, there are several protocols aimed to make cells artificially competent when conditions for natural competence are unknown. Two main methods are used to prepare artificially competent cells: 1) through chemical treatment of cells and 2) exposing the cells to electric pulses (electroporation). The former uses different chemicals depending on the procedure to create attraction between the DNA and the cell surface, while the latter uses electric fields to generate pores in the bacterial cell membrane through which DNA molecules can enter. The most efficient approach for chemical competence is incubation with divalent cations, most notably calcium (Ca2+) (4,5) Calcium-induced competence is the procedure that will be described here (6). This method is mainly used for transformation of Gram-negative bacteria, and that will be the focus of this protocol.
The procedure of chemical transformation involves a series of steps in which cells are exposed to cations to induce chemical competence. These steps are subsequently followed by a temperature change - heat shock - that favors the uptake of foreign DNA by the competent cell (7). The bacterial cell envelopes are negatively charged. In Gram-negative bacteria like Escherichia coli, the outer membrane is negatively-charged due to the presence of lipopolysaccharide (LPS) (8). This results in repulsion of the similarly negatively-charged DNA molecules. In chemical competence induction, positively-charged calcium ions neutralize this charge repulsion enabling DNA absorbance onto the cell surface (9). Calcium treatment and incubation with DNA are done on ice. Subsequently, an incubation at higher temperatures (42°C), the heat shock, is performed. This temperature imbalance further favors the DNA uptake. Bacterial cells need to be at the mid-exponential growth phase to withstand the heat shock treatment; in other growth stages the bacterial cells are too sensitive to the heat resulting in loss of viability which significantly decreases transformation efficiency.
Different DNA sources can be used for transformation. Typically, plasmids, small circular, double-stranded DNA molecules, are used for transformation in most laboratory procedures in E. coli. For plasmids to be maintained in the bacterial cell after transformation, they need to contain an origin of replication. This allows them to be replicated in the bacterial cell independently from the bacterial chromosome. Not all the bacterial cells get transformed during the transformation procedure. Thus, transformation yields a mixture of transformed cells and non-transformed cells. To distinguish between these two populations, a selection method to identify the cells that have acquired the plasmid is used. Plasmids usually contain selectable markers, which are genes encoding a trait that confers an advantage for growth (i.e. resistance to an antibiotic or chemical or rescue from a growth auxotrophy). After transformation, bacterial cells are plated on selective media, which only allows for growth of the transformed cells. In the case of cells transformed with a plasmid conferring resistance to a given antibiotic, the selective media will be growth media containing that antibiotic. Several different methods can be used to confirm that the colonies grown in the selective media are transformants (i.e. have incorporated the plasmid). For example, plasmids can be recovered from these cells using plasmid preparation methods (10) and digested to confirm plasmid size. Alternatively, colony PCR can be used to confirm the presence of the plasmid of interest (11).
The aim of this experiment is to prepare E. coli DH5α chemically competent cells, using an adaptation of the calcium chloride procedure (12), and to transform them with the plasmid pUC19 to determine transformation efficiency. The E. coli strain DH5α is a commonly used strain in molecular biology applications. Because of its genotype, specifically the recA1 and endA1, this strain allows for increased insert stability and improve the quality of plasmid DNA in subsequent preparations. Since the transformation efficiency decreases with increasing size of the DNA, the plasmid pUC19 was used in this protocol because of its small size (2686 bp) (see https://www.mobitec.com/cms/products/bio/04_vector_sys/standard_cloning_vectors.html for a vector map). pUC19 confers resistance to ampicillin and thus, this was the antibiotic used for selection.

Although TE is dependent on many factors, non-commercial competent cell preparations, like this one, normally yield 106 to 107 transformants per microgram of plasmid. Therefore, this preparation, with a TE = 2.46 x 108 cfu/&#181;g, yielded a TE well beyond the expected range. Additional protocols are available for making supercompetent cells when higher transformation efficiencies are required for a given application (13).
<p class="jo...

Source: Natalia Martin1, Andrew J. Van Alst1, Rhiannon M. LeVeque1, and Victor J. DiRita1
1 Department of Microbiology and Molecular Genetics, Michigan ...

Bacteria are remarkably adaptable and one mechanism which facilitates this adaptation is their ability to take in external DNA molecules. One type of DNA that bacteria can uptake is called a plasmid, a circular piece of DNA that frequently contains useful information, such as antibiotic resistance genes. The process of bacteria being modified by new genetic information incorporated from an external source is referred to as transformation. Transformation can easily be performed in the laboratory using Escherichia coli, or E. coli.In order to be transformed, E. coli cells must first be made competent, which means capable of taking in DNA molecules from their environment. The protocol for accomplishing this is surprisingly simple, a short incubation of the cells in a calcium chloride solution. This incubation causes the cells to become permeable to DNA molecules. After the cells are pelleted by centrifugation, the supernatant is removed. The plasmid DNA is now added to the competent cells. After incubating the cells with DNA, the mix is briefly heated to 42 degrees Celsius, followed by rapid cooling on ice. This heat shock causes the DNA to be transferred across the cell's wall and membranes. The cells are then incubated in fresh media. Then, the bacteria are placed at 37 degrees to allow them to reseal their membranes and express resistant proteins.Those cells which have taken in the plasmids will faithfully copy the DNA and pass it to their progeny and express any proteins that might be encoded by it, including antibiotic resistance mediators. Those resistance genes can be used as selectable markers to identify bacteria which have been successfully transformed because cells that have not taken up the plasmid will not express the resistance gene product. This means that when the cells are plated on a solid medium which contains the appropriate antibiotic, only cells that have taken up the plasmid will grow. Transformation of the cells in a growing colony can be further confirmed by culturing those cells in liquid media overnight to increase the yield before extracting the DNA from the sample. Once the DNA is isolated, a diagnostic restriction enzyme digest can be carried out. Because restriction enzymes cut DNA in predictable locations, running these digests on a gel should show a predictable pattern if the desired plasmid was successfully transformed. For example, if pUC19 is prepared and cut with the restriction enzyme HindIII, a single band of 2686 nucleotides should be seen on the gel.In this lab, you will transform E. coli strain DH-5 Alpha with pUC19, and then confirm the successful transformation by DNA gel electrophoresis.Before starting the procedure, put on the appropriate personal protective equipment, including a lab coat and gloves. Next, sterilize the workspace with 70% ethanol.Now, prepare chemically competent cells by depositing a loopfull of bacteria onto a sterile LB agar plate and streaking the bacteria with a new loop. Then, incubate the plate at 37 degrees Celsius overnight. The next day, sterilize the bench top with 70% ethanol again, and remove the plate from the incubator.Inoculate a single, well-isolated colony into 3 milliliters of LB broth in a tube with a sterile loop. Then, grow the culture at 37 degrees Celsius overnight, with shaking at 210 RPM. The next day, measure the optical density of the overnight culture with a spectrophotometer. Then, add 100 milliliters of LB broth to a one-liter flask, and inoculate it with the overnight culture at an optical density of 0. 01. Now, incubate the culture at 37 degrees Celsius with shaking, and check the OD600 every 15 to 20 minutes until the culture reaches mid-exponential growth phase.After approximately three hours, transfer 50 milliliters of the culture to two ice-cold polypropylene bottles. Then, place the bottles back on ice for 20 minutes to cool. Next, recover the cells via centrifugation. Discard the supernatants and place the bottles upside down on a paper towel. Next, resuspend the bacterial pellet in five milliliters of ice-cold calcium chloride magnesium chloride solution and swirl carefully until the pellet has dissolved completely. Then, add another 25 milliliters of the solution to the dissolved bacterial pellet. Resuspend the other bacterial pellet as previously demonstrated. After this, repeat the centrifugation, and remove the supernatants.If the competent cells are going to be directly transformed, resuspend each bacterial pellet in two milliliters of an ice-cold 0.1 molar calcium chloride solution by swirling the tubes carefully. To begin the transformation procedure, transfer 50 microliters of competent cells to two labeled 1.5 milliliter polypropylene tubes. Then, add one microliter of pUC19 plasmid DNA to one of the tubes. Mix gently, avoiding bubble formation, and incubate both tubes for 30 minutes on ice. After incubation, transfer the tubes to a heat block and incubate at 42 degrees Celsius for 45 seconds. Immediately transfer the tubes to ice, and incubate for two minutes. Now, add 950 microliters of SOC media to each tube and incubate them for one hour at 37 degrees Celsius to allow the bacteria to recover, and express the antibiotic resistant marker encoded in the plasmid.To make a 1 to 100 dilution, add 990 microliters of SOC media and 10 microliters of cell suspension to a 1.5 milliliter tube. Then, make a 1 to 10 dilution by adding 900 microliters of SOC media and 100 microliters of cell suspension to a 1.5 milliliter tube. Next, plate 100 microliters of the diluted cell suspensions and 100 microliters of the negative control, onto separate selective plates containing ampicillin using a spreader and incubate the plates at 37 degrees Celsius for 12 to 16 hours. After incubation, count the colony-forming units, or CFUs, per plate, obtained through transformation, and record these data. To verify that the transformants have the pUC19 plasmid, pick a single, well-isolated colony from a plate with a sterile loop, and introduce it to a tube containing 3 milliliters of LB broth. Then, incubate the culture at 37 degrees Celsius with shaking, overnight. The next day, use a DNA mini prep kit to isolate DNA from 3 milliliters of the culture, according to the manufacturer's instructions. After completing the DNA mini prep, digest the 1 microgram of purified pUC19 with a restriction enzyme at 37 degrees Celsius for 1 hour. Now, load 20 microliters of a molecular weight ladder, 1 microgram of digested plasmid DNA, and 1 microgram of undigested plasmid DNA into consecutive wells of a 1% agarose gel containing 1 microgram per milliliter ethidium bromide. Then, run the gel for 1 hour at 95 volts. Finally, visualize the gel with a UV illuminator.In this experiment, E. coli DH5 Alpha chemically competent cells were prepared using an adaptation of the calcium chloride procedure, and then transformed with the plasmid pUC19 to determine transformation efficiency. To calculate the transformation efficiency, use the recorded CFU counts for the 1 in 100 and 1 in 10 dilutions, and any other dilutions with CFU counts between 30 and 300. First, the recorded CFU count, 246 in this example, is divided by the amount of DNA, .0001 micrograms here, that was plated. Then, this number is divided by the dilution factor used to give the transformation efficiency in CFUs per microgram. In this example, a 1 to 10 dilution was used and 100 microliters of a 1 milliliter solution was plated, giving a final dilution factor of 0.01. In the undigested plasmid lane, the circular DNA may appear as two or three different bands of varying brightness. This is because the circular, uncut DNA may exist in several different conformation states, such as supercoiled, open circle, or more linear, and each of these move through the gel at different rates. Analysis of the recovered plasmid DNA digestion indicated that the plasmid used has an expected size of pUC19 DNA, 2,686 base pairs.

Education

JoVE Science Education

Advanced Biology

Microbiology

calcium chloride dna uptake in e. coli

Calcium chloride treatment can help E. coli take up foreign DNA. This chemical transformation method is used in molecular biology to move a plasmid into bacterial cells and then identify the cells that received it. The protocol described here uses chemically competent E. coli DH5α cells and the plasmid pUC19 to measure transformation efficiency.

Bacteria can exchange genetic material through horizontal gene transfer. The three main routes are transformation, transduction, and conjugation. Transformation is the process in which bacteria take up free DNA from the environment. In the lab, it usually includes four steps: preparing competent cells, mixing cells with DNA, recovering the cells, and plating them so transformants can grow.

For transformation to occur, cells must be competent, which means they can take in DNA. Some bacteria become naturally competent under certain conditions. Others do not, or the conditions are not known. For that reason, scientists often make cells artificially competent. Two common approaches are chemical treatment and electroporation, which uses electric pulses to open pores in the cell membrane.

This protocol uses calcium ions, especially Ca2+, to create chemical competence. It is mainly used with Gram-negative bacteria. E. coli cells and their outer membrane carry negative charge, and DNA is also negatively charged. Calcium helps neutralize this repulsion so DNA can attach to the cell surface. The cells and DNA are kept on ice during this step, and then a heat shock at 42°C helps drive DNA into the cells.

The cells must be in mid-exponential growth phase before heat shock. At other growth stages, they are more sensitive to heat and may lose viability. That lowers transformation efficiency. The DNA used for transformation is usually a plasmid, which is a small circular double-stranded DNA molecule. To stay in the cell after transformation, the plasmid must have an origin of replication so it can copy itself independently of the bacterial chromosome.

Not every cell becomes transformed, so the result is a mix of transformed and non-transformed cells. To find the cells that received the plasmid, the procedure uses selection. Plasmids often carry selectable markers, such as antibiotic resistance genes or genes that rescue a growth need. After transformation, the cells are plated on selective media. In this case, the media contains ampicillin, which allows only the transformed cells to grow.

Calcium Chloride DNA Uptake in E. coli

creating a winogradsky column: a method to enrich the microbial species in a sediment sample

creating-winogradsky-column-method-to-enrich-microbial-species

Winogradsky Column Microbial Layers and Gradients

A Winogradsky column shows how microbial layers form in mud and water over time. It is a clear, enclosed ecosystem that helps scientists grow sediment microbes that are hard to culture in a test tube or on a petri dish. By keeping conditions close to a microbe’s natural habitat, the column makes it possible to study organisms that help drive Earth’s biogeochemical cycles. The column is built from pond or wetland sediment mixed with water in a transparent container. Extra sources of carbon,...

serial dilutions and plating: microbial enumeration

serial-dilutions-and-plating-microbial-enumeration

Counting Bacteria with Dilution Plates

Counting bacteria with dilution plates helps microbiologists estimate how many cells are in a sample. Because bacteria can grow quickly and may be hard to count directly, serial dilution and plating make the concentration easier to measure. These methods have been used for more than a century to study bacterial and viral loads in clinical, industrial, pharmaceutical, and academic labs. Serial dilution reduces a sample in steps. A small volume of the original solution is moved into a fixed...

enrichment cultures: culturing aerobic and anaerobic microbes on selective and differential medias

enrichment-cultures-culturing-aerobic-anaerobic-microbes-on-selective

Selective Media for Bacterial Isolation

Selective media help scientists isolate bacteria by supporting some microbes and blocking others. This lab also uses differential media, which reveal a visible chemical trait in the organism being grown. Together, these methods help identify bacteria from mixed samples. Prokaryotic cells live in almost every environment on Earth. They also show wide metabolic diversity, so the growth medium must supply the molecules they need for energy. Some microbes are extremophiles, meaning they live in...

pure cultures and streak plating: isolation of single bacterial colonies from a mixed sample

pure-cultures-streak-plating-isolation-single-bacterial-colonies-from

Streak Plate Method for Isolating Bacteria

The streak plate method is used to isolate single bacterial colonies from a mixed sample. It helps separate one bacterial type from another so a pure culture can be grown. This is important in both clinical and research settings, where bacteria often grow together in mixed cultures. Pure cultures are needed for later genetic and protein studies. They are also used to check whether a sample is pure and to identify infectious agents from clinical samples. Because different strains can affect...

16s rrna sequencing: a pcr-based technique to identify bacterial species

16s-rrna-sequencing-pcr-based-technique-to-identify-bacterial

Bacterial ID with 16S rRNA Gene Sequencing

Bacterial identification with 16S rRNA gene sequencing helps scientists tell bacterial species apart. It is used in microbial ecology to study biodiversity in environmental samples and in medical microbiology to help diagnose infected patients. Traditional methods include microscopy, growth on specific media, biochemical and serological tests, and antibiotic sensitivity assays. Molecular methods have changed how bacteria are identified. 16S ribosomal RNA (rRNA) gene sequencing is often faster...

growth curves: generating growth curves using colony forming units and optical density measurements

growth-curves-generating-growth-curves-using-colony-forming-units

Bacterial Growth Stages and Cell Counts

Bacterial growth stages and cell counts show how a culture changes over time. This page follows a batch culture as it moves through lag, exponential, stationary, and death phases. It also shows how colony forming units, or CFU, and optical density can be used to measure that growth. Lag phase is the time bacteria need to adjust to a new environment before fast division begins. During exponential phase, cells grow and divide at the fastest rate, and DNA replication, RNA transcription, and...

antibiotic susceptibility testing: epsilometer tests to determine mic values of two antibiotics and evaluate antibiotic synergy

antibiotic-susceptibility-testing-epsilometer-tests-to-determine-mic

Measuring Bacterial Resistance with E-Tests

Measuring bacterial resistance with E-tests helps show how strongly an antibiotic can stop growth. The method is used to find the minimal inhibitory concentration, or MIC, which is the lowest antibiotic level that prevents visible bacterial growth. It is a practical way to study resistance in bacteria and compare how different antibiotics perform. The E-test uses a plastic strip that contains a built-in antibiotic gradient. The strip is placed on an agar plate that has been inoculated with...

microscopy and staining: gram, capsule, and endospore staining

microscopy-and-staining-gram-capsule-and-endospore-staining

Bacterial Stains for Cell Walls and Spores

Bacterial stains help scientists see cell walls, capsules, and endospores with a compound light microscope. Many bacteria are hard to tell apart with light alone because they are small, colorless, and can look similar under the lens. Staining makes these hidden features visible and helps identify different bacteria. A compound microscope uses more than one lens to magnify a sample. Its objective lens collects light near the specimen, and the eyepiece enlarges the image. Many compound...

plaque assay: a method to determine viral titer as plaque forming units (pfu)

plaque-assay-method-to-determine-viral-titer-as-plaque-forming-units

Phage Plaque Test for Counting Viruses

Bacteriophages, or phages, are viruses that infect prokaryotic cells. The plaque assay is a classic way to count these viruses by measuring viral titer, which is the amount of virus in a sample. It was first described in 1952 and is still one of the most reliable methods for determining viral titer. Phages were identified in the early 20th century by Twort and d'Hérelle. They have since been recognized for their therapeutic value and for their role in human and global ecosystems. Interest in...

Calcium chloride treatment can help E. coli take up foreign DNA. This chemical transformation method is used in molecular biology to move a plasmid into bacterial cells and then identify the cells that received it. The protocol described here uses chemically competent E. coli DH5α cells and the plasmid pUC19 to measure transformation efficiency. Bacteria can exchange genetic material through horizontal gene transfer. The three main routes are transformation, transduction, and conjugation.

conjugation: a method to transfer ampicillin resistance from donor to recipient e. coli

conjugation-method-to-transfer-ampicillin-resistance-from-donor-to

Bacterial Gene Transfer by Conjugation in E. coli

Bacterial conjugation is a form of horizontal gene transfer in E. coli that moves DNA from one cell to another through direct contact. It was first discovered by Lederberg and Tatum in 1946. Unlike transformation or transduction, conjugation is a natural, one-way transfer of DNA from a donor cell to a recipient cell. This process can increase bacterial genetic diversity. It is often described as a type of bacterial mating. It has also helped drive the spread of antibiotic-resistant bacteria.

phage transduction: a method to transfer ampicillin resistance from donor to recipient e. coli

phage-transduction-method-to-transfer-ampicillin-resistance-from

Using P1 Phage to Move Antibiotic Resistance in E. coli

Bacteriophage transduction moves DNA between bacteria by using a phage, or bacterial virus, as the carrier. In this process, a phage can deliver genetic material from one bacterium to another. The method is a form of horizontal gene transfer and is important in both bacterial evolution and laboratory genetics. Phages were first described in the early 1900s, and transduction was named in 1951 by Norton Zinder and Joshua Lederberg. The transcript describes two main phage classes. Lytic phages...

microbiology

This collection demonstrates the key tools of microbiological investigation, including proper sterile technique and plating, how to use selective media and enrich samples, and culturing methods for mixed or pure samples. Additionally, it looks at common methods for identifying microbial isolates, as well as procedures for the genetic manipulation of bacteria.

See how calcium chloride makes E. coli competent for DNA uptake, then use heat shock and ampicillin selection to identify transformants.

Calcium Chloride DNA Uptake in E. coli | JoVE K12

Natalia Martin

Andrew J. Van Alst

Rhiannon M. LeVeque

Victor J. DiRita

Department of Microbiology and Molecular Genetics

Michigan State University

Concepts

Performing the Experiment

Results

Genetic Lingo

Overview

An organism is diploid if it inherits two variants, or alleles, of each gene, one from each parent. These two alleles constitute the genotype ...

Punnett Squares

Overview

A Punnett square displays the possible genotypes offspring can inherit from two parental genotypes. If a trait&#x2019;s inheritance pattern ...

Monohybrid Crosses

Overview

In the 1850s and 1860s, Gregor Mendel investigated inheritance by performing monohybrid crosses in pea plants. He crossed two plants that were ...

Dihybrid Crosses

Overview

To determine whether traits are inherited together or separately, Gregor Mendel crossed pea plants that differed in two traits. These parental ...

Law of Segregation

When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 ...

Law of Independent Assortment

While Mendel&#x2019;s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how ...

Test Cross

Alleles are different forms of the same gene. Humans and other diploid organisms inherit two alleles of every gene, one from each parent.

An allele is ...

Pedigree Analysis

Overview

A pedigree is a diagram displaying a family&#x2019;s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or ...

Use Mendel's laws of segregation and independent assortment to analyze patterns of inheritance.

SC.912.L.16.1

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel&#8217;s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A ...

Chi-square Analysis

The chi-square test is a statistical hypothesis test. It is used to check whether there is a significant difference between an expected value and an ...

Multiple Allele Traits

Incomplete Dominance

Gregor Mendel&#39;s work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid ...

Lethal Alleles

Agouti: A Lethal Allele
Lucien Cu&#233;not discovered lethal alleles in 1905 while studying the inheritance of coat color in mice. The agouti gene is ...

Polygenic Traits

background-and-environment-affect-phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as ...

Discuss observed inheritance patterns caused by various modes of inheritance, including dominant, recessive, codominant, sex-linked, polygenic, and multiple alleles.

SC.912.L.16.2

Base-pairing and DNA Repair

The DNA Replication Fork

Lagging Strand Synthesis

The Replisome

Proofreading

Synthesis of new DNA molecules is carried out by the enzyme DNA polymerase, which adds nucleotides on the daughter strand complementary to the template ...

Replication in Prokaryotes

DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to the ...

Replication in Eukaryotes

In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before ...

Describe the basic process of DNA replication and how it relates to the transmission and conservation of the genetic information.

SC.912.L.16.3

The DNA Helix

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most viruses. DNA ...

Mutations

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. Mutations ...

Mutation, Gene Flow, and Genetic Drift

In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions ...

Explain how mutations in the DNA sequence may or may not result in phenotypic change. Explain how mutations in gametes may result in phenotypic changes in offspring.

SC.912.L.16.4

What is Gene Expression?

A gene is a stretch of DNA that serves as the blueprint for functional RNAs and proteins. Since DNA is comprised&#160; of nucleotides and proteins are ...

RNA Structure

The basic structure of RNA consists of a string of ribonucleotides attached by phosphodiester bonds. Although most RNA is single-stranded, it can form ...

Types of RNA

Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs perform diverse ...

Transcription

Transcription is the synthesis of RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene sequence. ...

Bacterial RNA Polymerase

Eukaryotic RNA Polymerases

General Transcription Factors

Tissue-specific transcription factors contribute to diverse cellular functions in mammals. For example, the gene for beta globin, a major component of ...

RNA Polymerase II Accessory Proteins

Transcription Elongation Factors

pre-mrna-processing-modification-of-pre-mrna-ends

Pre-mRNA Processing: Modification of pre-mRNA Ends

In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or ...

Pre-mRNA Processing: RNA Splicing

Transfer RNA Synthesis

Ribosomal RNA Synthesis

The Nucleolus

Additional Subnuclear Structures

Translation

Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following transcription, it constitutes ...

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

tRNA Activation

Initiation of Translation

Termination of Translation

Improving Translational Accuracy

Nonsense-mediated mRNA Decay

Molecular Chaperones and Protein Folding

The Proteasome

Regulated Protein Degradation

Proteins: From Genes to Degradation

Explain the basic processes of transcription and translation, and how they result in the expression of genes.

SC.912.L.16.5

Chromatin Structure and RNA Splicing

Alternative RNA Splicing

Nuclear Export of mRNA

Discuss the mechanisms for regulation of gene expression in prokaryotes and eukaryotes at transcription and translation level.

SC.912.L.16.6

Molecular Cloning

Molecular cloning is a set of methods, which are used to insert recombinant DNA into a vector - a carrier of DNA molecules that will replicate recombinant ...

An Overview of Genetic Engineering

Genetic engineering &#8211; the process of purposefully altering an organism&#8217;s DNA &#8211; has been used to create powerful research tools and model ...

Recombineering and Gene Targeting

One of the most widely used tools in modern biology is molecular cloning with restriction enzymes, which create compatible ends between DNA fragments that ...

bacterial-transformation-the-heat-shock-method

Bacterial Transformation: The Heat Shock Method

Transformation is the process that occurs when a cell ingests foreign DNA from its surroundings. Transformation can occur in nature in certain types of ...

Bacterial Transformation: Electroporation

The term &#x201C;transformation&#x201D; refers cellular ingestion of foreign DNA.  In nature, transformation can occur in certain types of bacteria.  In ...

An Introduction to Transfection

Transfection is the process of inserting genetic material, such as DNA and double stranded RNA, into mammalian cells. The insertion of DNA into a cell ...

Conjugation: A Method to Transfer Ampicillin Resistance from Donor to Recipient E. coli

Source: Alexander S. Gold1, Tonya M. Colpitts1
1 Department of Microbiology, Boston University School of Medicine, National Emerging Infections Diseases ...

Phage Transduction: A Method to Transfer Ampicillin Resistance from Donor to Recipient E. coli

CRISPR

Bacterial Transformation

Background

In early 20th century, pneumonia was accountable for a large portion of infectious disease deaths1. In order to develop an effective vaccine ...

Bacterial Transformation
ExpandFirst, ensure that each student or student group has a filled ice bucket.
Then, set up a tube rack for each work station.
...

Bacterial Transformation
ExpandIMPORTANT: In addition to wearing the appropriate personal protective equipment, be sure to take care to keep your face ...

Describe how viruses and bacteria transfer genetic material between cells and the role of this process in biotechnology.

What is the Cell Cycle?

The cell cycle refers to the sequence of events occurring throughout a typical cell&#8217;s life. In eukaryotic cells, the somatic cell cycle has two ...

Interphase

The cell cycle occurs over approximately 24 hours (in a typical human cell) and in two distinct stages: interphase, which includes three phases of the ...

Explain the relationship between mutation, cell cycle, and uncontrolled cell growth potentially resulting in cancer.

SC.912.L.16.8

A. DNA stores and transmits genetic information. Genes are sets of instructions encoded in the structure of DNA.

B. Genetic information is passed from generation to generation by DNA in all organisms and accounts for similarities in related individuals.

C. Manipulation of DNA in organisms has led to commercial production of biological molecules on a large scale and genetically modified organisms.

D. Reproduction is characteristic of living things and is essential for the survival of species.

Calcium Chloride DNA Uptake in E. coli

Description

Transcript

Tags

More videos by Standards