1. Bacterial Transformation
Plate 27
Bacterial Transformation

2. Genetic Change Bacterial DNA can undergo changes in several ways:
Transformation
Conjugation
Transduction

3. Transformation History
1928, a British bacteriologist and medical officer named Frederick Griffith first demonstrated bacterial transformation
Streptococcus pneumoniae (AKA “pneumococcus”) can exist in several strains:
“S” strain – smooth, encapsulated, deadly
“R” strain – rough, unencapsulated, harmless

5. Griffith’s Experiment
Injected mice with the “S” strain of bacteria
Result: dead mice
Injected mice with the “R” strain of bacteria
Result: no sickness or death
Injected mice with heat-killed “S” strain of bacteria

6. Griffith’s Experiment1. 2. 3.

7. Griffith’s Experiment4.
Injected mice with a mixture of harmless “R” strain bacteria and heat-killed “S” strain bacteria
Result: dead mice

8. Bacterial Transformation
In order for bacterial transformation to occur, there needs to be:
“naked DNA”: DNA not found in a cell (“extracellular” DNA)
“competent” bacterial cells: ability to take up extracellular DNA

9. Bacterial Transformation
In Griffith’s experiment, segments of the genetic information from the “S” strain bacteria became “naked” when the cells were heat-ruptured

10. Bacterial Transformation
“Competent” bacteria cells take up DNA segments through their cell membranes
Some bacteria cells are naturally “competent”
Some bacteria cells can become artificially “competent” through chemicals, heat-shocking, and electro-shocking

11. Bacterial Transformation
Enzymes within the cell cut a segment from the newly acquired DNA
The segment gets inserted into the cell’s own DNA
In Griffith’s experiment, genes from the “S” strain were transferred to the “R” strain, making it harmful

13. Transformation

15. What do you think?
What kinds of applications can bacterial transformation have?
In other words, how can people benefit from the use of this technology?