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 hill.com/sites/ /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