STUDENT ACTIVITY - PGLO GENETIC (DNA) TRANSFORMATION
INTRODUCTION
Genetic transformation literally means change caused by genes, and involves the insertion of a gene
into an organism in order to change the organism’s trait. Remember, a gene is a piece of DNA which
provides the instructions for making (coding for) a particular protein. This protein gives an organism a
particular trait. Genetic transformation is used in many areas of biotechnology. In medicine, diseases
caused by defective genes are beginning to be treated by gene therapy; that is, by genetically
transforming a sick person’s cells with healthy copies of the defective gene that causes the disease.
Genetic engineering is the addition of relatively short segments of DNA to a living cell. In this
experiment, you will insert new DNA into the bacterium
E. coli to give it new characteristics. The DNA you will be placing into the cells is incorporated into a
plasmid. A plasmid is a small, circular piece of DNA that is not part of the bacteria’s regular genes. In
nature, bacteria often exchange plasmids that contain genes that allow bacteria to become resistant to
an antibiotic. Scientists have exploited this process allowing us to add specific genes to plasmids, put
the plasmids into bacteria, and use the bacteria as “factories” to make large amounts of the gene
product.
In this lesson we will insert pGLO plasmid DNA into bacterial cells (E. coli) which are normally sensitive
to the antibiotic ampicillin (or “cancer” in our theme – both kill the E. coli bacterium, and don't glow in
the dark).
pGLO GENETIC (DNA) TRANSFORMATION
The pGLO plasmid contains a gene (bla) that makes the bacteria resistant to or fight off the antibiotic
ampicillin (cancer) and a gene (GFP) that makes a protein that glows in the dark when it is exposed to
UV light. The GFP gene can be switched on in transformed cells by adding the sugar arabinose (ara) to
the nutrient agar, allowing the green florescent protein to be produced. This gene is included only as a
visual signal that the bacteria has been transformed. When Scientists put a plasmid into a bacterial cell
like this they call it “transformation”. They change (transform) the normal bacteria into bacteria that
glow in the dark and survive ampicillin (cancer). The source of the GFP gene is the bioluminescent
jellyfish, Aequorea Victoria.
SIMPLIFIED PROCEDURE:
To INSERT pGLO DNA into E-Coli Bacteria:
1.
2.
3.
4.
5.
6.
7.
Label two microtubes: 1) +pGlo 2) No pGlo
Add 250 ul transformation solution into each tube; put on ice
Put E-coli bacteria into each tube (follow detailed directions below)
Put pGlo plasmid into the +pGlo tube only
Insert pGlo into E-coli by putting tubes in ice, then heat shocking for 50sec and reinserting into ice.
Streak the E-coli bacteria onto plates prepared with food (LB agar), arabinose and/or Ampicilin
Incubate plates for 24 hr, then observe.
pGLO GENETIC (DNA) TRANSFORMATION
DETAILED PROCEDURE
Prepare the E-coli bacteria to absorb the pGlo plasmid (one tube will not get the pGlo plasmid so the
E-coli bacteria is used as a control).
1. Label one closed micro test tube +pGLO and another -pGLO. Label both tubes with your group’s
name. Place them in the foam tube rack.
2. Open the tubes and, using a sterile transfer pipet, transfer 250 µl of transformation solution (CaCl2)
into each tube. This solution helps the bacteria receive the plasmid.
3. Place the tubes on ice.
pGLO GENETIC (DNA) TRANSFORMATION
4. Use a sterile loop to pick up a single colony of bacteria from your starter plate. Pick up the +pGLO
tube and immerse the loop into the transformation solution at the bottom of the tube. Spin the
loop between your index finger and thumb until the entire colony is dispersed in the transformation
Adapted from pGLO transformation Lab from Bio-Rad for Arizona Bioengineering Collaboration/2002
solution (with no floating chunks). Immediately place the loop in 10% bleach. Place the tube back
in the tube rack in the ice. Using a new sterile loop, repeat for the -pGLO tube.
5. Examine the pGLO DNA plasmid solution with the UV lamp. Note your observations. Have your
teacher add 10 µL of the plasmid solution to the +pGLO tube. Mix the loopful into the cell
suspension of the +pGLO tube. Close the tube and return it to the rack on ice. Also close the -pGLO
tube. Do not add plasmid DNA to the -pGLO tube. Why not?
pGLO GENETIC (DNA) TRANSFORMATION
6. Incubate the tubes on ice for 10 minutes. Make sure to push the tubes all the way down in the rack
so the bottom of the tubes stick out and make contact with the ice.
Adapted from pGLO transformation Lab from Bio-Rad for Arizona Bioengineering Collaboration/2002
7. While the tubes are sitting on ice, identify you labeled LB nutrient agar plates (this is the food (LB)
for the bacteria to eat) on the bottom (not the lid) as follows:
• One LB/amp plate: + pGLO
• One LB/amp/ara plate: + pGLO
• One LB/amp plate: - pGLO
• Label the LB plate: - pGLO (This is the control, so we excluded it!)
8. Heat shock. Using the foam rack as a holder, transfer both the (+) pGLO and (-) pGLO tubes into the
water bath, set at 42C, for exactly 50 seconds. Make sure to push the tubes all the way down in the
rack so the bottom of the tubes stick out and make contact with the warm water. After 50 seconds,
immediately place both tubes back on ice. For the best transformation results, the transfer from
the ice (0°C) to 42°C and then back to the ice must be rapid. Incubate tubes on ice for 2 minutes.
pGLO GENETIC (DNA) TRANSFORMATION
9. Remove the rack containing the tubes from the ice and place on the bench top. Open a tube and,
using a new sterile pipet, add 250 µl of LB nutrient broth to the tube and reclose it. Repeat with a
new sterile pipet for the other tube. This broth dilutes the transformation solution and allows the
bacteria to begin to grow Incubate the tubes for 10 minutes at room temperature. Use this down
time to clean your station.
Adapted from pGLO transformation Lab from Bio-Rad for Arizona Bioengineering Collaboration/2002
10. Tap the closed tubes with your finger to mix. Using a new sterile pipet for each tube, pipet 100 µl of
the transformation and control suspensions onto the appropriate nutrient agar plates.
pGLO GENETIC (DNA) TRANSFORMATION
11. Use a new sterile loop for each plate. Spread the suspensions evenly around the surface of the LB
nutrient agar by quickly skating the flat surface of a new sterile loop back and forth across the plate
surface. DO NOT PRESS TOO DEEPLY INTO THE AGAR. Allow the plates to sit undisturbed for a few
minutes.
Adapted from pGLO transformation Lab from Bio-Rad for Arizona Bioengineering Collaboration/2002
12. Stack up your plates and tape them together. Put your group name and class period on the bottom
of the stack and place the stack of plates upside down in the 37°C incubator until the next day.
Adapted from pGLO transformation Lab from Bio-Rad for Arizona Bioengineering Collaboration/2002
pGLO GENETIC (DNA) TRANSFORMATION
DAY 2 - STUDENT OBSERVATIONS
1. Observe the results of your transformation experiment after it has been incubated for more than 24
hrs, and draw growth patterns on the diagram below. What color are the bacteria? Record the
number of bacterial colonies there are on each plate (the spots you see.) Use the UV lamp in a darken
room to observe transformed bacteria.
Control Plates
Observations
Number of
Colonies
- Plasmid
LB
- Plasmid
LB/amp
Transformation Plates
Plates
+ Plasmid
LB/amp
+ Plasmid
LB/amp/ara
Adapted from pGLO transformation Lab from Bio-Rad for Arizona Bioengineering Collaboration/2002
Questions to consider for your conclusion and analysis:
1. Compare and contrast the number of colonies on each of the following pairs of plates? What
does each pair of results tell you about the experiment?
a. LB and LB/AMPb. LB/AMP+ and LB/AMPc. LB/AMP and LB/AMP/ARA
2. What two factors must be present in the bacteria’s environment for you to observe the green
color?
3. What was the purpose of heat shocking the bacteria? (when you placed it on ice, then in the
42C water bath and back on ice?)
4. What factors (things) might prevent the bacteria from taking in the pGLO plasmid?
5. Were you successful in creating a “new” bacterium? What was your proof?
6. Transformation efficiency is expressed as the number of bioluminescent colonies per microgram
of pGLO. Because transformation is limited to only those cells that are competent, increasing
the amount of plasmid used does not necessarily increase the probability that a cell will be
transformed. A sample of competent cells is usually saturated with small amounts of plasmid
and excess DNA may actually interfere with the transformation process.
a.
b.
Determine the total mass of pGLO used. ___________________________ (You used 15 ul
of pGLO at a concentration of 0.005 ug/ul.) Total Mass = volume X concentration
Calculate the total volume of cell suspension prepared. _______________
c.
Now calculate the fraction of the total cell suspension that was spread on the plate.
(Number of ul spread/total volume) ______________________
d.
Determine the mass of pGLO in cell suspension. ____________________ (Total mass of
pGLO X fraction spread.)
e.
Determine the number of colonies per ug of plasmid. Express in scientific notation.
(Number of colonies observed/mass pGLO spread [from calculation in step (d)] = transformation
efficiency). This is the transformation efficiency.
f.
What factors might influence transformation efficiency? Explain the effect of each
factor you mention.
7. What are some practical uses for this technology?
8. How do scientists engineer the pGLO plasmids used in this lab?
Now that you have successfully transformed bacteria to make it glow, you can assume
that it also contains the desired DNA protein.
Adapted from pGLO transformation Lab from Bio-Rad for Arizona Bioengineering Collaboration/2002