Zero to Genetic Engineering Hero - Chapter 3 - Growing E. coli Cells 68
1920s, the K12 strain has gone through much evolu-
tion and manipulation in labs to become the lab strain
we take for granted today.
Recall learning about plasmids at the end of Chapter
1; the short circular DNA helix loops that are akin to
a USB stick for cells. In addition to a 4,600,000 nucle-
otide “main” chromosome, natural E. coli have a large
plasmid called an “F plasmid” (short for “Fertility
factor plasmid”). This plasmid enables one bacte-
ria to share DNA with another through a process
called bacterial conjugation - it allows the bacteria to
communicate with one another. In lab strains of K12
E. coli, these F plasmids have been removed by scien-
tists, making it very difcult for the bacteria to share
genetic information. This substantially reduces the
risk of K12 bacteria sharing information with other
organisms if they are released into the environment.
It also prevents communication between organisms
in your samples during your experiments. K12 E. coli
is not only a scientically-sound organism choice, it
is also a responsible one.
As you will learn in coming chapters, genetic engi-
neers sometimes use antibiotic resistance genes
during the genetic engineering process. A question
that sometimes arises in public discussion is whether
the antibiotic resistance genes used in genetic engi-
neering cause the emergence of “superbugs” resistant
to all antibiotics. The short answer is no, and one of
the main reasons for this is that lab strains of E. coli
have been “gagged” by the engineers - they cannot
really share their DNA with other cells thanks to the
removal of the “F plasmid”.
A second signicant difference between Lab K12 E. coli
and other forms of E. coli is that they no longer have a
“lambda phage” infection. Lambda phage is a virus
that infects E. coli and becomes part of its genome
(Figure 3-15). Yes, even bacteria can get viruses and
catch a cold! The original K12 strain has the lambda
phage in its genome. Under the right conditions, the
virus can become active, kill the cells and spread to
others. Lab strains of K12 E. coli no longer have this
infection, and you do not have to worry about your
bacteria catching a cold during your experiments.
Throughout the 1950s-1980s, experiments were
completed to rst remove lambda phage and then the
F plasmid, as well as a few other genes to achieve a
version of K12 E. coli called “MG1655”. Further tweak-
ing to this bacteria has led to the most widely used
E. coli K12 bacteria strains, called DH5α and DH10β.
Labs have made hundreds of other versions of E. coli
to study more about how cells work, but the DH5α and
DH10β versions remain the most commonly used in
genetic engineering. These are the E. coli strains you
will be using and encounter in this book. For now, the
K12 E. coli that you have already used in the hands-on
exercise and whose ancestor was originally isolated
from the feces of someone at Stanford University
in California, about 100 years ago will be the model
organisms we study.
Figure 3-15. The lambda phage is a virus that can infect E. coli.
Microflora Going Deeper 3-4
Microora is the name given to all of the microorganisms in and on the human body that coexists with you
and, in most cases, keep you healthy. Microora may also be called ‘normal ora’ or your ‘microbiome.’ E.
coli is just one of the hundreds of different kinds of bacteria that live on your skin, in your armpits, eyes,
mouth, intestines, and even on your hair. In the 19th and 20th centuries, the consensus was that most, if not
all, bacteria were bad. However, in the 21st century, we now know that all the bacteria in our microbiome
(E. coli included) are essential for our health.
If you’re interested in learning about your microbiome, you can use one of the many consumer microbiome
testing services available online for non-medical purposes. Typically, the testing company will send you a
swabbing kit and, after swabbing your body, you send it back for analysis using next-generation genomic
sequencing. Once analyzed by the company, you can then go to your online account to view the results. Fun!
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