Plate 29
Bacterial Transduction
Genetic Changes
• 3 ways to alter the DNA within bacteria:
– Bacterial transformation
• Indirect: cell  extracellular fluid  cell
– Bacterial conjugation
• Direct: cell  cell
– Bacterial transduction
• Indirect: cell  virus  cell
Bacteriophage
• Bacteriophage: a virus that
specifically infects bacteria
• Phage – Greek for “to eat”
• Perhaps the most numerous
“living thing” in the world
• Composed of a protein
capsid surrounding its DNA
• Sometimes used as an
alternative to antibiotics
Generalized Transduction – Step 1
• Bacteriophages attach to specific receptors on
the surface their host cell (they are species
specific)
Generalized Transduction – Step 2
• Phage injects its DNA
into the host bacteria
cell
Generalized Transduction – Step 3
• Phage DNA instructs bacteria
to create “fragmentation
enzymes” to break up the
host cell’s DNA
• The bacteria cell begins
building new phages,
according to the phage DNA’s
instructions
• Some bacterial DNA
segments are accidentally
incorporated into the new
phage’s DNA
Generalized Transduction – Step 4
• Virus cycle culminates with lysis (rupturing) of
the host cell
• Hundreds of new bacteriophages are released,
ready to infect other bacteria cells
Generalized Transduction – Step 5
• New phages infect other bacteria cells and
inject their DNA into the new host cell
• If phage contained bacterial DNA from
previous host, it may be incorporated into the
new host cell’s DNA (like in conjugation)
• New phages do not form
Specialized Transduction
• Some phages incorporate their DNA in the
host cell’s DNA and don’t immediately
assemble new phages
Specialized Transduction
• A chemical or a change in the host cell’s
conditions signal the assembly of new phages
• When the phage DNA detaches from the host
cell DNA, it occasionally brings some bacterial
DNA with it
Specialized Transduction Animation
http://highered.mcgrawhill.com/sites/0072556781/student_view0/chap
ter17/animation_quiz_3.html
Specialized Transduction
• The new phages (with some bacterial DNA)
leave the host cell when it lyses (ruptures)
• Other bacterial cells can now be infected with
the new hybrid DNA
Generalized vs. Specialized
Transduction
• Generalized transduction is generalized
because any of the host cell’s DNA can be
incorporated into a new phage (it’s random)
• Specialized transduction is specialized because
only the host cell DNA that is next to the
phage DNA can form in new phages