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Bio97_09+L17 - II Bio Sci 97 Lecture 17 Dr Carrie Brachmann...

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1 ©2007 C. Brachmann 1 Genetics of Bacteria and Bacteriophages  II Bio Sci 97 Lecture 17 Dr. Carrie Brachmann Office hours today 12-1:30 McGaugh Hall 4213 REVISED TIME Monday, 11/9: 1-2:30 Friday, 11/13 and Monday 11/16 12-1:30
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2 ©2007 C. Brachmann 2 Lysogenic Cycle No progeny phage particles are produced Prophage: The phage DNA when it is inserted into bacterial chromosome (red in figure above) A phage DNA molecule is transmitted to each bacterial progeny cell upon normal cell division Lysogen : surviving bacterial cell that is resistant to subsequent phage infection prophage can be induced into the lytic cycle (irradiation) H&J 7.22
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3 ©2007 C. Brachmann 3 H&J 7.22, .25, .26 Lys o g e nizatio n  by phag e   λ cos: cohesive ends that are complementary and allow the linear molecule to  circularize
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4 ©2007 C. Brachmann 4 Occasionally bacterial genes get packaged into phage coat and these phage particles are called transducing phages
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5 ©2007 C. Brachmann 5 Fig. 7.16 phag e  DNA, like   bac te rial c hro m o s o m e  is   do uble -s trande d Transducing phages transfer bacterial DNA into a new host where it may be integrated by recombination. The recipient becomes leu+ but doesn’t die from a phage infection. Why doesn’t it die?
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6 ©2007 C. Brachmann 6 There is a huge variety of phages and each is specific for a type of bacteria. i.e. P22 infects Salmonella typhimurium P1 infects Escherichia coli
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7 ©2007 C. Brachmann 7 Phage Therapy? Deadly E. coli O157:H7 Researchers working on ways to keep it out of our food. It replicates in intestines of livestock. They tried infecting sheep with E. coli O157:H7, but two days later they couldn’t isolate the bacterium from the sheep. A student realized that the protection could come from a phage in the animal’s intestine. Isolated CEV-1, a bacteriophage.
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8 Conjugation- F factor, pillus, unidirectional Transposition- IS elements, transposons, transposase, R plasmid Transduction- phage, faulty head stuffing Transformation
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9 ©2007 C. Brachmann 9 Transformation transformant 1 in 10 3  to 1 in 10 8 Pieces of4 Natural  transformation Engineered  transformation
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10 Conjugation- F factor, pillus, unidirectional Transposition- IS elements, transposons, transposase, R plasmid Transduction- phage, faulty head stuffing Transformation- bacteria take up and integrate exogenous DNA into genome
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11 No colonies phe trp met + his + phe + trp + met his LA-22 LA-2 Colonies plate on nutrient agar plates prototrophic bacteria must be phe+ trp+  met+ his+ Question for thought Which of the 4 mechanisms best describes this experiment?
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12 Mapping genes in the  bacterial chromosome
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13 ©2007 C. Brachmann 13 Conjugation can transfer genes from the bacterial chromosome In the 1950s, Luca Cavalli-Sforza discovered a strain of E. coli that was very efficient at transferring chromosomal genes Hfr (for High frequency of recombination) Hfr strains are derived from F + strains in which the F factor plasmid has integrated into the chromosome
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14 ©2007 C. Brachmann
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