Bacterial Plasmids and Conjugation

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Lecture 9 Bacterial Plasmids and Conjugation
Chapter 13 pp. 288 291 296 299
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Plasmids

• Characteristics
• Small
• Double stranded
• Circular

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Plasmids

• Characteristics
• Independent of the genome
• Stably inherited
• Not necessary for survival

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Plasmids

• Fertility Factors
• Fertility or F plasmid
• Involved in conjugation

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Metabolism
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Plasmids

• Resistance Factors
• R Factors or plasmids
• Confer antibiotic resistance to the cell that
  contains these plasmids

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Plasmids

• Col Plasmids
• Contain genes for the production of colicins
• Provide a selective advantage

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Plasmids

• Virulence Plasmids
• Make bacteria more pathogenic
• E.G enterotoxins carried by E. coli

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Plasmids

• Metabolic Plasmids
• Aid bacteria in metabolism
• E.G Lactose and Nitrogen fixation and Nodulation

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Metabolism
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Conjugation

• Lederberg and Tatum
• Showed that genetic information could be
  transferred from one bacterium to another
• Conjugation

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Conjugation

• Davis
• Showed Conjugation requires direct, physical
  contact between cells

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Conjugation

• Hayes
• Conjugation is polar
• Requires the F plasmid
• Recipient becomes F once conjugation is complete

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Conjugation

• Hayes
• Noted that only rarely did auxotrophs become
  prototrophs after conjugation

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Conjugation

• Hfr Strains
• Integration of F into the genome

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Conjugation

• Consequences of Hfr conjugation
• Can transfer bacterial genes other than the F
  genes
• Many different genes could be transferred
• Recombination or Genetic variability

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