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Microbial genetics: recombination and plasmids

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Last revised: Friday, January 7, 2000
Ch. 14 in Prescott et al, Microbiology, 4th Ed.
Note: These notes are provided as a guide to topics the instructor hopes to cover during lecture. Actual coverage will always differ somewhat from what is printed here. These notes are not a substitute for the actual lecture!
Copyright 2000. Thomas M. Terry

Gene transfer and Recombination

General problem




Mechanisms for transforming cells without natural competence systems


Mechanism of generalized transduction

Use of phage P1 as a "gene truck"


Properties of Plasmids

Examples of Plasmid genes

  1. Antibiotic resistance genes (enzymes that modify or degrade antibiotics) -- plasmids with these genes are called R factors
  2. Heavy metal resistance (enzymes that detoxify metals by redox reactions)
  3. Growth on unusual substrates (enzymes for hydrocarbon degradation, etc.)
  4. Restriction/modification enzymes (protect DNA, degrade unprotected DNA)
  5. Bacteriocins (proteins toxic to other bacteria lacking the same plasmid)
  6. Toxins (proteins toxic to other organisms; e.g. humans) -- called virulence plasmids. Some Examples:
    1. Staph aureus virulence factors: coagulase, hemolysin, enterotoxin, others
    2. pathogenic E. coli strains: hemolysin, enterotoxin
  7. Proteins that mediate plasmid transfer to uninfected strains

Conjugative Plasmid transfer

 F-factors: F+, F-, and Hfr strains

Mating of Hfr with F-

Linear and Circular genetic maps

Applications of conjugation mapping

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