DNA can be exchanged among bacteria through conjugation, transduction, or transformation. Transformation involves bacteria taking up naked DNA directly from their environment. Competent bacterial cells are able to undergo transformation, incorporating extracellular DNA. In 1928, Griffith discovered pathogenic pneumococci could be transformed into a nonpathogenic form by a "transforming principle" from killed pathogenic bacteria. Transformation is used in DNA cloning to make multiple copies of DNA and produce human proteins like insulin.

1. DNA TRANSFORMATION
Jonh Banda (group one)
 DNA exchange among bacteria
DNA can be exchanged among bacteria in
three ways;
1. CONJUGATION; this is transfer of
genetic material between bacterial cells
by direct cell to cell contact or by a
bridge like connection between two
cells.
2. TRANSDUCTION; a phage carries DNA
from one bacterium to another.
3. TRANSFORMATIOM; cells Take up free
DNA directly from their environment,.

2. TRANSFORMATION
Incorporation of naked DNA from
extracellular environment.
Cells that can be used for
transformation are called competent
cells ,
Transformation is different from the
other two mentioned ways of dna
exchange among bacteria’s, because
competent cells takes the dna that is
the environment that is not bind to any
cell .

3. The diagram below shows how
the three ways differ

4. HISTORY ON HOW DNA
TRANSFORMATION CAME UP
 In 1928, Fred Griffith found that one form
of the pathogenic pneumococci (now
called streptococcus pneumoniae ) could
be mysteriously (transformed) into
another form.
 Griffith made a conclusion that the dead
pathogenic bacteria gave off a
transforming principle that changed the
live nonpathogenic rough colony forming
bacteria into the pathogenic smooth
colony form.

5. Cells called competent
Competent cells have the ability of
being competence. What does
competence mean?
• Competence
• The ability of some bacteria to take up
naked DNA from their environment
• It is genetically programmed.
Generally ,more than a dozen genes
are involved ,encoding both regulation
and structural components. Steps
involved are different from gram

6. Steps that are involved

7. Types of transformation
There are two types of transformation
1. Natural transformation
2. Artificial transformation.
NATURAL TRANSFORMATION
In this case DNA take up occurs without
outside help
Naturally competent bacterium, they can
take up DNA from the environment without
requiring special treatment.
 About 40 species have been found to be
naturally competent or transformable.
 Example ,bacillus subtilis ,streptococcus
pneumonia, Hemophilus influenzas,
Neisseria gonorrhoeae, etc.

8. Steps involved in natural
transformation
1. Following proteins are involved in the
process.
 ComEA; binds directly extracellular
double stranded DNA,
 comFA provides the energy for
translocation of DNA through the
membrane.
 comEA, comEC, and comFA form a sort
of ATP
 The genes in the comG operon encode
proteins that might form a pseudopilus
which helps move DNA through the
comEA DNA binding protein, and then
retract,drawing the DNA into the cell.

9. The comE ,comF and comG operons are
all under the transcriptional control of
comK
Some of genes involved in the
transformation process are not designated
as com, because such genes were first
discovered on the basis of their
involvement in other processes
1. The nucA gene product makes double
strands breaks in extracellular DNA
2. Other examples are single stranded
DNA binding protein (SSB), and RecA
functions in the recombination of
transforming DNA chromosome DNA.

10. Image showing steps involved in
natural transformation

11.  The length of the single stranded DNA
incorporated into the recipient
chromosome are about 8.5 to 12kb on
cotransfoemation genetic markers
 Incorporation takes only few minutesto
be completed.

12. Natural transformation of gram
positive bacteria

13. negative gram bacteria

14. ARTIFICIALLY INDUCED
COMPETENCE
 Bacteria can be sometimes be made competent by
certain chemical treatment or DNA can be forced into
becteria by a strong electric field in a process celled
electroporation,
1. Chemical treatment (with calcium ions)
 Chemically induced transformation is usually inefficient
and only a small percentage of the cells are ever
transformed
 The cells must be plated under conditions ,selective for
transformed cells.
 Therfore the DNA used for should contain a selectable
gene such as encoding resistance to an antibiotic.
1. Electroporation
 The bacteria are mixed with DNA and briefly exposed to
a strong electric firld.
 The bacteria are washed extensively in buffer with very
low ionic strength such as distilled water.

15. ARTIFICIAL
TRANFORMATION

16. APPLICATION OF
TRANSFORMATION
 Bacterial transformation is used
1. To make multiple copies of DNA
called DNA cloning
2. To make large amounts of specific
human protein for example human
insulin which can be used to treat
people with typle I diabetes

17. Question to see if you have
understood
1. A competent cell can take up linear
DNA from its surrounding ,
True or false
1. Describe the theory of
transformation of a bacterial cell with
a plasmid.
2. What will happen to the cells if they
are not kept cold while preparing
competent cells.
3. Define a competent cell and its
transformation