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Plate 27 Bacterial Transformation Genetic Change • Bacterial DNA can undergo changes in several ways: – Transformation – Conjugation – Transduction 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 Griffith’s Experiment 1. Injected mice with the “S” strain of bacteria • Result: dead mice 2. Injected mice with the “R” strain of bacteria • Result: no sickness or death 3. Injected mice with heat-killed “S” strain of bacteria • Result: no sickness or death Griffith’s Experiment 1. 2. 3. Griffith’s Experiment 4. Injected mice with a mixture of harmless “R” strain bacteria and heat-killed “S” strain bacteria • Result: dead mice 4. 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 Bacterial Transformation • In Griffith’s experiment, segments of the genetic information from the “S” strain bacteria became “naked” when the cells were heat-ruptured 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, heatshocking, and electro-shocking 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 Transformation 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?