Gene Transfer
Gene transfer in bacteria
•
1.
2.
3.
There are three types of gene transfer
Transformation
Conjugation
Transduction
All types of gene transfer
• Involve unidirectional transfer of
information (donor-->recipient)
• Require the integration of newly acquired
DNA “homologous recombination”
• Increases genetic diversity
What happens to DNA that is not
integrated within a replicon?
DNA integrated can be inherited
Griffith’s experiments with
Streptococcus pneumoniae
Transformation
• Requires competent
cells to uptake DNA
• Need living cells and
source of DNA
Conjugation
• Transfer of genes
between 2 bacterial
cells
• Gram negative cells
use a sex pilus
• F(+) cells have F
plasmid, F(-) lack F
plasmid
Conjugation between (F+)
and F(-) cells
F plasmid can integrate into the
chromosome creating Hfr cell
Hfr cell can also become a F’ cell
Conjugation between Hfr
cell and F(-)
• Does transfer of DNA
occur?
• How is it different
from F(+) X F(-)?
• **Note:figure #4 is
wrong, should have an
Hfr cell and a F(-)
recombinant cell
Transduction
• Transfer of genes between a phage and a
bacterial cell
• Generalized transduction: occurs with lytic
or lysogenic phage (section 8.7)
• Specialized transduction: occurs with
lysogenic phage (section 13.3)
Generalized Transduction
Specialized Transduction
• What type of phage is
involved?
• Will it result in
generation of new
phage?
Comparison of mechanisms of DNA transfer
The Mobile gene pool
• In E. coli, 75% of genes are found in all
strains
• Rest of the genome is made up of the
mobile gene pool or mobilome
• Mobile gene pool made from plasmids,
transposons, or phage DNA
Plasmids
• Found in many types
of organisms as
dsDNA
• Provide the cell new
characteristics
Resistance Plasmids (R plasmids)
Transposons…way to move
genes between organisms
• How did this S. aureus
become Vancomycin
resistant S. aureus
(VRSA)?