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.mcgraw-hill.com/sites/0072556781/student_view0/chapter17/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